JP5576806B2 - Fixing device and image forming apparatus having the fixing device - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus including the fixing device.

  In a fixing device using a fixing member such as a fixing roller or a fixing belt, heating is started by a heating means such as a heater lamp or a ceramic heater until the fixing member reaches a fixing temperature and becomes ready for a fixing operation. In order to shorten the warm-up time, there has been proposed a method for reducing the loss due to heat radiation generated when heat is supplied to the fixing member by heating the surface and the inner surface of the fixing member while directly contacting with the heating means. Yes.

  For example, in JP-A-2002-333788 (Patent Document 1), as shown in FIG. 3, a fixing belt 100 as a fixing member is heated while being brought into contact with a heating member 101 such as a planar heating element. A fixing device 102 that shortens the warm-up time has been proposed.

  However, in Patent Document 1, there is a case where there is a limit to shortening the warm-up time. Therefore, a core, such as an iron core, is passed through the fixing roller formed of a conductive material in the axial direction of the fixing roller, and a coil is wound around the core. It is also considered to use a low-frequency induction heating method in which a magnetic flux is generated in the coil by energizing the current, an eddy current is induced in the fixing roller by the action of the magnetic flux, and the fixing roller is sufficiently heated. .

JP 2002-333788 A

  However, when such a low frequency induction heating method is applied to a fixing device using a fixing member having a thickness as thin as 1 mm or less like a fixing belt, the fixing belt cannot be heated sufficiently.

  This is because, in the case of heating by electromagnetic induction, there is a frequency dependence on the thickness. Therefore, if the fixing belt is thin, a large eddy current can be induced if it is a high-frequency AC current. This is because the induced eddy current is small and the calorific value is small.

  Therefore, when using a low-frequency alternating current, the induced eddy current and the amount of heat generated can be increased by increasing the thickness of the fixing belt. Therefore, the thickness of the heating member that comes into contact with the fixing belt is increased.

  The present invention has been made in view of the above problem, and a fixing device in which a heating member is disposed on the inner side of a fixing belt is in contact with an inner peripheral surface of the heating member, and a core, By providing a heating means composed of a coil wound around the core, if a low-frequency alternating current in the audible frequency band is energized to the coil, it will contact the core by the action of magnetic flux generated in the coil. It is an object of the present invention to provide a fixing device that can sufficiently heat a heating member that contacts the fixing belt and a fixing belt that contacts the heating member via the heating member, and an image forming apparatus including the fixing device.

The present invention relates to an endless fixing belt stretched between a fixing member and a heating member, temperature detection means for detecting the surface temperature of the fixing belt, and opposed pressure contact with the fixing member via the fixing belt. The heating device includes a heating unit, and the heating unit includes a core in contact with and in contact with an inner peripheral surface of the heating member, and the core. The coil comprises a coil that is wound, and has a power source for energizing the coil with a low-frequency alternating current in an audible frequency band .

  The present invention is characterized in that a plurality of the heating means are arranged in the width direction of the fixing belt.

  In the present invention, it is preferable that a plurality of the heating means are disposed so as to partially overlap in the width direction of the fixing belt.

  In the present invention, it is preferable that the heating unit includes a control unit that controls energization for each coil.

  In addition, the present invention is characterized by using an image forming apparatus including the fixing device.

  According to the present invention, a fixing device in which a heating member is disposed on the inner side of the fixing belt includes a core that is in contact with and in contact with an inner peripheral surface of the heating member, and a coil wound around the core. If a low-frequency alternating current in the audible frequency band is supplied to the coil, the heating means that is in contact with and contacts the core by the action of the magnetic flux generated in the coil is provided. The fixing belt that comes into contact with the heat can also be sufficiently heated.

1 is a schematic cross-sectional view illustrating a configuration of a fixing device of the present invention. FIG. 6 is a schematic diagram illustrating a state in which a plurality of heating hands are arranged in the width direction of the fixing belt. (A) A state where heating means are arranged in a line is shown. (B) A state where the heating means is arranged in a staggered arrangement is shown. (C) A state in which the heating means is disposed at an angle with a predetermined angle. FIG. 9 is a schematic diagram illustrating a configuration of a fixing device as a conventional example of the present invention.

  Hereinafter, a fixing device according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing a configuration of a fixing device 1 of the present invention. Hereinafter, the fixing device 1 of the present invention will be described, but it goes without saying that a general technique of an image forming apparatus can be applied to other configurations.

  The fixing device 1 includes a fixing roller 2 that is a fixing member, a pressure roller 3 that is a pressure member, a fixing belt 4, a heating unit 5, and a heating member 6. In the fixing device 1, the fixing belt 4 is stretched between the fixing roller 2 and the heating member 6, and the pressure roller 3 is disposed so as to be in pressure-contact with the fixing roller 2 through the fixing belt 4. The fixing roller 2 and the heating member 6 are disposed so as to be substantially parallel in the axial direction of the fixing roller 2.

  In the fixing device 1, the heating member 6 comes into contact with the fixing belt 4 to heat the fixing belt 4, and the recording paper P as a recording medium is predetermined in a fixing nip portion N formed by the fixing roller 2 and the pressure roller 3. This is an apparatus for fixing the unfixed toner image T carried on the recording paper P by heating and pressing on the recording paper P when passing in the advancing direction Y0 at the fixing speed or the copying speed. In this embodiment, the length of the fixing nip N in the conveyance direction of the recording paper P is 7 mm, and the fixing speed is 225 mm / sec.

  The unfixed toner image T is a developer (such as a non-magnetic one-component developer (non-magnetic toner), a non-magnetic two-component developer (non-magnetic toner and carrier), or a magnetic developer (magnetic toner). Toner). The fixing speed is the process speed, and the copying speed is the number of copies per minute. Further, when the recording paper P passes through the fixing nip portion N, the fixing belt 4 comes into contact with the toner image carrying surface of the recording paper P.

  The fixing roller 2 presses against the pressure roller 3 via the fixing belt 4 to form a fixing nip portion N, and at the same time, is provided so as to be rotatable around a rotation axis. The fixing roller 2 rotates in the rotation direction Y1 following the rotation of the fixing belt 4.

  The fixing roller 2 has an axial length of 320 mm and a diameter of 30 mm, and has a two-layer structure in which a core metal 2 a and an elastic layer 2 b are formed in order from the inside. The core metal 2 a includes, for example, iron, stainless steel, and the like. A metal such as steel, aluminum, copper, or an alloy thereof is used. Moreover, a rubber material having heat resistance such as silicone rubber and fluorine rubber is suitable for the elastic layer 2b. In this embodiment, the force when the fixing roller 2 is pressed against the pressure roller 3 via the fixing belt 4 is about 216 N, the core metal 2 a is stainless steel having a diameter of 15 mm, and the elastic layer 2 b is thick. A 7.5 mm thick silicone sponge rubber was used.

  The pressure roller 3 conveys the fixing belt 4 by being driven to rotate in the rotation direction Y2 around the rotation axis by a drive motor (not shown). The pressure roller 3 has a diameter of 30 mm and has a three-layer structure in which a core metal 3a, an elastic layer 3b, and a release layer 3c are formed in this order from the inside. For the metal core 3a, for example, a metal such as iron, stainless steel, aluminum, copper, or an alloy thereof is used. Further, a rubber material having heat resistance such as silicone rubber and fluorine rubber is suitable for the elastic layer 3b, and PFA (a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) or PTFE (PTFE) is suitable for the release layer 3c. A fluororesin such as polytetrafluoroethylene is suitable.

  In this embodiment, the core metal 3a is 24 mm in diameter and 2 mm thick STKM (carbon steel pipe for machine structural use), the elastic layer 3 b is 3 mm thick silicone solid rubber, and the release layer 3 c is 30 μm thick PFA. What was a tube was used.

  In addition, a heater lamp 3 d for heating the pressure roller 3 is disposed inside the pressure roller 3. The control means 200 that controls the temperature of the fixing operation of the fixing device 1 supplies power to the heater lamp 3d from a power supply circuit (not shown), whereby the heater lamp 3d emits light and infrared light is emitted from the heater lamp 3d. As a result, the inner peripheral surface of the pressure roller 3 absorbs infrared rays and the entire pressure roller 3 is heated. In this embodiment, a heater lamp 3d with a rated power of 300 W was used.

  When the fixing roller 2 rotates, the fixing belt 4 follows the fixing roller 2 and rotates in the rotation direction Y3. The fixing belt 4 is heated to a predetermined temperature by the heating member 6 and heats the unfixed toner image T and the recording paper P passing through the fixing nip portion N. In this embodiment, the surface temperature of the fixing belt 4 is set to 175 ° C.

  The fixing belt 4 is an endless belt having a length of 315 mm and a diameter of 50 mm, is stretched around the heating member 6 and the fixing roller 2, and is wound around the fixing roller 2 at a predetermined angle θ.

  The predetermined angle θ is a point at which the fixing belt 4 starts to move away from the fixing roller 2 from the straight line connecting the point where the fixing belt 4 starts to contact the fixing roller 2 and the axis of the fixing roller 2 by the rotation of the fixing belt 4. And a straight line connecting the axis of the fixing roller 2 and is 185 ° in this embodiment.

  The fixing belt 4 is formed by forming an elastomer material such as silicone rubber having excellent heat resistance and elasticity as an elastic layer on the surface of a base material made of a heat resistant resin such as polyimide or a metal material such as stainless steel or nickel. In addition, a three-layer structure in which a fluororesin such as PFA or PTFE having excellent heat resistance and releasability is formed as a release layer. Alternatively, a fluororesin may be internally added to the base polyimide in contact with the heating member 6. Thus, the sliding load with the heating member 6 can be reduced, and when the fixing belt 4 slides, the fixing belt 4 is prevented from meandering, and the durability of the fixing belt 4 is maintained high. be able to.

  In this embodiment, a fixing belt 4 in which a base material is 70 μm thick polyimide, an elastic layer is 150 μm thick silicone rubber, and a release layer is coated with a 30 μm thick PFA tube is used.

  Moreover, you may use aluminum instead of a polyimide as a base material. Since aluminum has high thermal conductivity, heat from the heating member 6 that contacts the fixing belt 4 can be easily supplied to the fixing belt 4. As a result, the fixing belt 4 can be sufficiently heated, and heating unevenness does not occur.

  Further, instead of polyimide, conductive powder such as carbon black or graphite may be dispersed in polyimide. Since the eddy current has already been induced in the fixing belt 4 by the action of the magnetic flux from the heating means 5, the fixing belt 4 generates heat by the carbon black itself generating heat by the eddy current. Therefore, heating unevenness of the fixing belt 4 does not occur, and the fixing belt 4 can be sufficiently heated.

  Further, in the fixing device 1, as temperature detection means, the peripheral surface of the fixing belt 4 is disposed on the center and end portions in the axial direction of the fixing roller 2, and the heating member side thermistors 10 a and 10 b are disposed on the peripheral surface of the pressure roller 3. A pressure roller-side thermistor 10c is provided to detect the surface temperature of each.

  Energization from the heating means 5 is controlled based on the surface temperature of the fixing belt 4 detected by the heating member side thermistors 10a and 10b. The energization from the heater lamp 3d is controlled based on the surface temperature of the pressure roller 3 detected by the pressure roller side thermistor 10c. The heating member side thermistors 10a and 10b and the pressure roller side thermistor 10c in this embodiment are contact-type temperature detection means, and are infrared detection type temperature sensors.

  The temperature detection results of the heating member side thermistors 10 a and 10 b and the pressure roller side thermistor 10 c are transmitted to the control means 200, and the control means 200 determines whether the fixing belt 4 and the pressure roller 3 are based on the respective temperature detection results. The energization to the heating means 5 and the heater lamp 3d is controlled so that the surface temperature approaches a predetermined temperature.

  Further, a thermostat or a thermal protector may be provided in the vicinity of the peripheral surface of the fixing belt 4 for detecting an abnormal temperature rise of the fixing belt 4 and cutting off the energization when the temperature exceeds a predetermined temperature.

  The heating means 5 includes a core 5a that is in contact with and in contact with the inner peripheral surface of the heating member 6, and a coil 5b wound around the core 5a.

  First, a magnetic flux is generated in the coil 5b when a low-frequency alternating current is supplied to the coil 5b from the power source 7 that supplies the coil 5b with an alternating current. The heating member 6 is heated by the action of the magnetic flux. The portion that is not in contact with the core 5a is heated by the propagation of heat. The fixing belt 4 is also heated via the heating member 6. Further, since the eddy current is induced in the fixing belt 4 by the action of the magnetic flux, the fixing belt 4 is heated without passing through the heating member 6.

  In this manner, the fixing belt 4 is heated via the heating member 6 and heated without the heating member 6 by the action of the magnetic flux generated in the coil 5b. The core 5a is an iron core used for a transformer or the like, and preferably has a high magnetic permeability such as ferrite, iron, magnetic stainless steel, silicon steel plate, electromagnetic steel plate, nickel steel. These are because heat generation is large when an eddy current is generated. In this example, a silicon steel sheet laminated iron core was used.

  In the present embodiment, the coil 5b is coated with a resin such as enamel, polyurethane, polyester, nylon, polyesterimide, and polyamideimide as an insulating layer on the surface of a copper wire having a thickness of 1.6 mm. You may use the litz wire which made a twisted wire. The resistance is preferably made as small as possible in order to suppress Joule loss in the coil 5b.

  The power source 7 is a commercial power source of 100V or 200V, and a low frequency alternating current of 50 Hz or 60 Hz is passed through the coil 5b as the frequency. The frequency may be a low frequency of 10 kHz or less which is an audible frequency band. .

  In the case of heating by electromagnetic induction, since there is a frequency dependence on the thickness, when the thickness is as thin as 1 mm or less as in the fixing belt 4, a large eddy current is induced by the heating means 5 if it is a high-frequency alternating current. However, in the low-frequency alternating current, the induced eddy current is small and the heat generation amount is small.

  That is, in order to increase the eddy current and the amount of heat generated by the heating means 5 using a low-frequency alternating current, the thickness of the fixing belt 4 may be increased. However, increasing the thickness of the fixing belt 4 is not preferable because cracks occur. Therefore, the thickness of the heating member 6 that contacts the fixing belt 4 is increased.

  As described above, even if the thickness of the fixing belt 4 is small, if the thickness of the heating member 6 is increased, the heating member 6 and the heating member are heated using electromagnetic induction at a low frequency of a commercial power source. 6 can sufficiently heat the fixing belt 4. On the contrary, if the high-frequency alternating current is used, the fixing belt 4 and the heating member 6 may be thin. However, the low-frequency commercial power supply is once rectified from alternating current to direct current and then converted into high-frequency alternating current. Must be provided separately.

  The heating member 6 has a substantially semicircular arc-shaped cross section with an outer diameter of 28 mm, and is composed of a base material layer 6 a and a surface layer 6 b in order from the inside of the fixing belt 4. In this example, STKM iron having a thickness of 2 mm was used as the base material layer 6a, and aluminum having a thickness of 100 μm was used as the surface layer 6b.

  The reason why iron is used as the base material layer 6a is to disperse heat over the entire peripheral surface of the heating member 6.

  The reason why aluminum is used as the surface layer 6b is that it has higher thermal conductivity than the iron of the base material layer 6a, so that the heating unevenness of the fixing belt 4 does not occur, and the fixing belt 4 is also heated sufficiently. can do. When copper having higher thermal conductivity than iron is used in advance as the base material layer 6a, the surface layer 6b need not be provided.

  In the present embodiment, aluminum having a high thermal conductivity is used as the surface layer 6b, but a conductive powder such as carbon black or graphite may be mixed. In this case, since the carbon black itself generates heat by the action of the magnetic flux from the heating means 5, the outer peripheral surface of the heating member 6 and the fixing belt 4 in contact with the heating member 6 can be sufficiently heated. Uneven heating will not occur.

  A fluororesin such as PFA or PTFE may be formed on the surface layer 6b as a coating layer in contact with the fixing belt 4. This is to reduce the frictional resistance between the heating member 6 and the fixing belt 4, so that wear of the fixing belt 4 can be prevented, the durability of the fixing belt 4 can be improved, and the fixing belt 4 is driven. The load on the fixing roller 2 and the pressure roller 3 to be performed can also be reduced. Thereby, durability of the fixing roller 2 and the pressure roller 3 can also be improved. Further, the adhesion between the fixing belt 4 and the surface of the heating member 6 is improved, and the heat transfer efficiency to the fixing belt 4 is increased, so that the fixing belt 4 can be driven with low power. Further, since the surface temperature of the fixing belt 4 becomes uniform and the surface pressure is adjusted, meandering of the fixing belt 4 can be suppressed.

  In the fixing device 1, an image formation instruction command from a CPU (Central Processing Unit) (not shown) which is a main control unit that controls all operations of the image forming apparatus, the heating member side thermistors 10 a and 10 b, and a pressure roller The temperature control of the fixing operation of the fixing device 1 is performed based on the temperature detection result of the side thermistor 10c and the abnormal temperature rise data of the fixing belt 4 detected by the thermostat or the thermal protector. This temperature control is performed by the control unit 200, and energization to the heating unit 5 and the heater lamp 3d is controlled so that the surface temperature of the fixing belt 4 and the pressure roller 3 approaches a predetermined temperature.

  The heating means 5 is energized by the control means 200 when a low-frequency alternating current is energized from the power source 7 to the coil 5b, and the heater lamp 3d is energized by a power circuit (not shown). Is done.

  In this embodiment, the power control is duty control that changes the ratio between the energized period and the non-energized period within a predetermined fixed period, but phase control that changes the half-wave phase of the low-frequency alternating current is performed. It may be used. The ratio between the energized period and the non-energized period may be appropriately adjusted according to the size and thickness of the recording paper P and the operation mode of the image forming apparatus.

  Although the control means 200 is centrally controlled by the CPU, the control means 200 may be provided in the CPU. The control means 200 includes a RAM (Random Access Memory) (not shown) that temporarily stores various data, and can be read as necessary. The image forming instruction is an instruction input from an operation panel provided in the image forming apparatus or an external device such as a computer connected to the image forming apparatus. By inputting the image forming instruction, the fixing device 1 is input. Starts the fixing processing operation.

  FIG. 2 is a schematic diagram illustrating a state in which a plurality of cores 5 a and coils 5 b of the heating unit 5 are disposed inside the fixing belt 4 and the heating member 6 in the width direction of the fixing belt 4.

  FIG. 2A shows a state in which the coils 5b are arranged in a row, FIG. 2B shows a state in which the coils 5b are partially arranged so that a part of the coils 5b overlaps, and FIG. It is the schematic which shows a mode that it arrange | positioned diagonally with a predetermined angle so that a part of coil 5b may overlap.

  2A, 2B, and 2C, the core 5a and the coil 5b of the heating unit 5 are arranged in the axial direction of the fixing belt 4. Heating unevenness does not occur in the axial direction, and the fixing belt 4 can be sufficiently heated.

  Further, if a plurality of control means 200 for controlling energization are provided for each coil 5b of the heating means 5, the heating can be controlled for each coil 5b, so that the temperature of the fixing belt 4 can be finely controlled and the image can be controlled. A good image without defects can be provided.

  Further, when the small size recording paper P is continuously printed, an excessive temperature rise does not occur at the end of the fixing belt 4 in the axial direction where the recording paper P does not pass, and the sizes are different. Correspondence to the recording paper P is possible.

  The energization control of the low-frequency alternating current with respect to each of the plurality of coils 5b can be easily controlled simply by disposing a switching element for each coil 5b. The switching element only needs to be switched ON / OFF, and this makes it possible to easily control the heating region in the width direction of the fixing belt 4.

  In FIG. 2A, since a plurality of cores 5 a and coils 5 b of the heating unit 5 are disposed inside the fixing belt 4 and the heating member 6 in the width direction of the fixing belt 4, There is no uneven heating in the width direction, and the fixing belt 4 can be sufficiently heated.

  In FIG. 2B, in the width direction of the fixing belt 4, the adjacent coils 5b1 and 5b2 are disposed so as to overlap each other, so that they are disposed so as not to overlap. Compared to the case, heating unevenness does not occur in the width direction of the fixing belt 4, and the fixing belt 4 can also be sufficiently heated. The cores 5a and the coils 5b of the heating means 5 are arranged in a staggered arrangement, but this is to arrange them freely according to the temperature distribution of the fixing belt 4, thereby fixing. Heating unevenness does not occur in the width direction of the belt 4.

  In FIG. 2C, the fixing belt 4 is disposed obliquely at a predetermined angle so that adjacent coils 5 b 3 and a part of the coil 5 b 4 overlap in the width direction of the fixing belt 4. Therefore, the unevenness of the heating does not occur in the width direction of the fixing belt 4.

DESCRIPTION OF SYMBOLS 1 Fixing device 2 Fixing roller 2a Core metal (3a)
2b Elastic layer (3b)
3 Pressure roller 3c Release layer 3d Heater lamp 4 Fixing belt 5 Heating means 5a Core 5b Coil (5b1 to 5b4)
6 Heating member 6a Base material layer 6b Surface layer 7 Power source 10a Heating member side thermistor (10b)
10c Pressure roller side thermistor 200 Control means N Fixing nip P Recording paper T Unfixed toner image Y0 Traveling direction (Y1, Y2, Y3)
θ Predetermined angle

Claims (5)

An endless fixing belt stretched between the fixing member and the heating member, temperature detection means for detecting the surface temperature of the fixing belt, and a pressure member that is in pressure-contact with the fixing member via the fixing belt A fixing device comprising:
The heating member includes a heating unit, and the heating unit includes a core in contact with and in contact with an inner peripheral surface of the heating member, and a coil wound around the core .
A fixing device comprising: a power source that supplies a low-frequency alternating current in an audible frequency band to the coil . The fixing device according to claim 1 , wherein a plurality of the heating units are arranged in a width direction of the fixing belt. The fixing device according to claim 2 , wherein the heating unit is disposed so as to partially overlap in the width direction of the fixing belt. It said heating means, fixing device according to claim 2 or 3, characterized in that it comprises a control means for controlling the energization for each of the coils. An image forming apparatus comprising: a fixing device according to any one of claims 1-4.