JP4760863B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device and an image forming apparatus, and more particularly to a technique for forming a fixing nip in the fixing device.

In recent years, electromagnetic induction heating type fixing devices are becoming popular as fixing devices in image forming apparatuses such as laser printers and copying machines.
FIG. 11 shows an example of the configuration of a conventional induction heating type fixing device (hereinafter referred to as “IH fixing device”) 100 (Patent Documents 1 and 2).
As shown in the figure, the fixing device 100 is configured such that the peripheral surface of the fixing belt 121 stretched around the rollers 122 and 123 is brought into contact with the circumferential surface of the pressure belt 131 stretched around the rollers 132 and 133. A fixing nip is formed, and a predetermined nip is formed by pressing the belt portion forming the fixing nip from above and below by pressing pads 124 and 134 disposed inside the circulation paths of the respective belts 121 and 131. The pressure is ensured.

The fixing belt 121 includes a dielectric heating layer, and the exciting coil unit 110 is disposed along the upper peripheral surface thereof. Due to the alternating magnetic flux generated by the exciting coil unit 110, an eddy current is generated in the heat generating layer of the fixing belt 121 to generate heat, and the toner image on the sheet S passed through the fixing nip is heat-fixed.
According to such a configuration of the IH fixing device 100, since the fixing belt 121 is directly heated, there is an advantage that the warming-up time is short and the heating efficiency is good as compared with the case where a heating element such as a halogen lamp is used.
JP 2003-84591 A JP 2003-91185 A

However, according to the above prior art, in the method of generating the nip pressure using the pressing members such as the pressing pads 124 and 134, the heat of the pressing pad itself is taken away by the heat capacity of the pressing pad itself, and the warm-up time is shortened. It was a hindrance.
Further, since the pressing pads 124 and 134 are rubbed with the fixing belt 121 and the pressure belt 131 in a state of being loaded with high pressure, wear is severe, the quality of the fixed image is disturbed, the pressing pad 124 as a pressing member, There are also problems of cost and maintenance due to replacement of the belt 134, the fixing belt 121, and the pressure belt 131. This problem can occur in the same manner when, for example, the heating-side rotator is configured by using a fixing roller instead of the fixing belt 121.

  The present invention has been made in view of the above-described problems, and in a fixing device in which at least a pressure-side rotating body has an endless belt shape, the amount of wear due to wear is reduced as much as possible, and maintenance labor is reduced. An object of the present invention is to provide a fixing device and an image forming apparatus provided with the fixing device that can reduce the warming-up time.

In order to solve the above-described problems, the fixing device according to the present invention forms a fixing nip by pressing the peripheral surface of the second rotating body on the peripheral surface of the first rotating body, and also includes the first rotating body. A fixing device that performs induction heating with a magnetic flux generated by an exciting coil, passes a sheet on which an unfixed image is formed, through the fixing nip, and thermally fixes the unfixed image, wherein the second rotating body includes: The belt comprises an endless belt including a ferromagnetic layer stretched by two or more rollers, and a magnetic force is applied to a portion of the belt constituting the second rotating body located at the fixing nip. Magnet means for generating an attractive force in the fixing nip direction and securing a nip pressure is provided , and the magnet means comprises a magnet coil and a DC voltage applying means for applying a DC voltage thereto, the excitation coil and the magnet Coil for the same position Wherein the wound formed by.

With the above configuration, the first rotating body is induction-heated by the magnetic flux generated by the exciting coil, and a repulsive force is applied to the first rotating body by the magnetic flux generated by the eddy current generated in the first rotating body by the induction heating. Magnetic force is generated by a magnet means having a magnet coil and a DC voltage applying means for applying a DC voltage to the portion located in the fixing nip of the second rotating body made of an endless belt containing a ferromagnetic material. Since the first and second rotating bodies are brought into pressure contact with each other by generating an attractive force in the fixing nip direction with respect to the second rotating body, a special pressing member can be secured. A sufficient nip pressure can be ensured without using.
As a result, it is possible to reduce maintenance by reducing the number of consumable parts, and it is possible to shorten the warm-up time by reducing the heat capacity of the fixing nip part.
In addition, since the exciting coil and the magnet coil are wound at the same position, the exciting coil and the magnet coil can be integrated, and space can be saved.
Furthermore, the nip pressure can be controlled by changing the applied DC voltage.
Here, the fixing device according to the present invention forms a fixing nip by pressing the peripheral surface of the second rotating body on the peripheral surface of the first rotating body, and the first rotating body with an exciting coil. A fixing device that performs induction heating with generated magnetic flux, passes a sheet on which an unfixed image is formed, through the fixing nip, and thermally fixes the unfixed image. And an endless belt including a ferromagnetic layer stretched by a roller, and a magnetic force is applied to a portion of the belt constituting the second rotating body located at the fixing nip so as to form the fixing nip. Magnet means for generating an attractive force in a direction and ensuring a nip pressure is provided, and the magnet means comprises a magnet coil and a DC voltage applying means for applying a DC voltage to the magnet coil, and an AC voltage applied to the excitation coil. , Output from the DC voltage application means By applying by superimposing a DC voltage, the excitation coil may be used also serves as the coil magnet.

As a result, sufficient nip pressure can be ensured without using a special pressing member, maintenance can be reduced by reducing consumable parts, and warming up can be achieved by reducing the heat capacity of the fixing nip. Time can be shortened.
In addition, by applying the DC voltage output from the DC voltage application means superimposed on the AC voltage applied to the excitation coil, the excitation coil is used also as a magnet coil, so that resource saving and further improvement are possible. It becomes possible to achieve space saving.
Furthermore, the nip pressure can be controlled by changing the applied DC voltage.
The first rotating body may be formed of an endless belt that does not include a ferromagnetic material and is stretched between two or more rollers.
Thereby, a fixing nip having a sufficient length in the belt circumferential direction can be secured.
Furthermore, the first rotating body may be a hollow roller, and the magnet coil may be disposed at a position facing the fixing nip of a hollow portion of the roller.

Thereby, space saving can be achieved .

Furthermore, the exciting coil may be formed by winding a litz wire, and the magnet coil may be formed by winding a single wire.
Thereby, each resistance at the time of an alternating current and a direct current flowing through a coil reduces, and an efficient exciting coil can be obtained .

Further, the a seat thickness acquisition means for acquiring information about the thickness of the sheet to be fed to the fixing nip, the DC voltage applying means, as a DC voltage is applied for different values depending on the thickness of the obtained sheet Also good.

Thereby, an appropriate nip pressure can be applied according to the difference in the thickness of the sheet.
Further, the sheet feeding timing obtaining means for obtaining the timing at which the sheet passes the fixing nip position is provided, and the voltage applying means applies a DC voltage to the magnet coil when the sheet passes through the fixing nip. It may be applied.
As a result, it is possible to save power without applying a DC voltage to the magnet coil except when the sheet passes through the fixing nip.

Further, the image forming apparatus further includes a sheet passing timing acquisition unit that acquires a timing at which a toner image formed on a sheet serving as a fixing counter image passes through a fixing nip position, and the voltage applying unit includes the toner image on the sheet. A DC voltage may be applied to the magnet coil when passing through the fixing nip.
Thereby, in order to generate the nip pressure even to the portion where the toner image of the sheet is not formed, a direct voltage is not applied to the magnet coil, and further power saving can be achieved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a fixing device and an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings, taking as an example a case where the embodiment is applied to a copying machine.
(1) Overall Configuration of Copying Machine FIG. 1 is a configuration diagram showing a schematic configuration of a copying machine 1 according to the present embodiment.
As shown in FIG. 1, the copying machine 1 includes a scanner unit 2 and a printer unit 3.

The copying machine 1 is a copy job for printing the image on the sheet S by the printer unit 3 based on the image data read by the scanner unit 2, or a print job sent from an external terminal via a network such as a LAN. Is received, the printer unit 3 has a function of executing a print job for printing the image.
The scanner unit 2 is a known image reading device that reads a set original image and obtains image data of the original. The printer unit 3 includes an image forming unit 10, a sheet feeding unit 20 having three sheet feeding cassettes 21 to 23, a fixing unit 30, a control unit 40, an AC voltage output unit 51 and a DC voltage output unit 52.

For printing in the printer unit 3, a toner image is formed on the photosensitive drum of the image forming unit 10, and the formed toner image is transferred onto the sheet S fed from one of the paper feeding cassettes. The toner image transferred onto the sheet S is heated and pressurized in the fixing unit 30 to be fixed on the sheet S and discharged outside the apparatus.
The AC voltage output unit 51 and the DC voltage output unit 52 generate predetermined AC voltage and DC voltage, respectively, and supply them to the exciting coil 371 (FIG. 3) of the fixing unit 30. In the present embodiment, a voltage in which the DC voltage output from the DC voltage output unit 52 is superimposed on the AC voltage output from the AC voltage output unit 51 is supplied.

  An operation panel 8 is disposed at an easy-to-operate position on the front side of the printer unit 3. The operation panel 8 is provided with a copy number key, a key for instructing execution of a job, and a display for displaying the contents of the job. For example, the user can set the type of sheets (thick paper, thin paper, etc.) stored in the paper feed cassettes 21 to 23 from the operation panel 8.

  A sheet detection sensor 6 that detects the leading edge of the sheet S being conveyed is disposed upstream of the fixing unit 30 in the sheet conveyance direction and along the sheet conveyance path. The sheet detection sensor 6 is, for example, a reflective optical sensor including a light emitting unit and a light receiving unit, and light emitted from the light emitting unit toward the conveyance path is reflected by the leading edge of the sheet being conveyed, and the reflected light is received. When the light is received by the unit, a tip detection signal indicating that is output. The tip detection signal is sent to the control unit 40.

(2) Configuration of Control Unit 40 FIG. 2 is a block diagram illustrating a configuration of the control unit 40.
As shown in the figure, the control unit 40 includes a CPU (Central Processing Unit) 41, a communication interface (I / F) unit 42, a ROM (Read Only Memory) 43, and a RAM (Random Access Memory) 44 as main components. , An EEPROM (Electrically Erasable and Programmable Read Only Memory) 45, an image memory 46, and the like.

The communication I / F unit 42 is an interface for connecting to a LAN (Local Area Network) such as a LAN card or a LAN board, and receives print job data from the outside.
The EEPROM 45 stores applied DC voltage value information and the like which will be described later. The RAM 44 is a work area for the CPU 41.

  The CPU 41 reads a necessary program from the ROM 43 and executes a copy job by controlling the operations of the scanner unit 2 and the printer unit 3 in a unified manner with timing. In addition to smoothly executing a print job based on the print job data received by the communication I / F unit 42, the output of the AC voltage output unit 51 and the DC voltage output unit 52 is controlled to control the excitation coil 371 of the fixing unit 30. Energize to. Furthermore, the sheet accommodation information input from the operation panel 8 by the user is received. The sheet accommodation information includes, for example, plain paper for the paper feed cassette 21, thick paper for the paper feed cassette 22, thin paper for the paper feed cassette 23, etc., for each paper feed cassette. This is information in which types are associated with each other. The sheet accommodation information is stored in the EEPROM 45. The CPU 41 can know the types of sheets stored in the paper feed cassette by referring to the information.

The image memory 46 stores image data read by the scanner unit 2, external print job data, and the like, and these data are read when the job is executed.
(3) Configuration of Fixing Unit 30 FIG. 3 is a diagram illustrating a configuration of the fixing unit 30.
As shown in the figure, the fixing unit 30 stretches the fixing belt 31, the driving roller 32 and the driven roller 33 for stretching the fixing belt 31, the pressure belt 34, and the pressure belt 34. This is a so-called IH type fixing device including a driving roller 35 and a driven roller 36, and a magnetic flux generator 37 disposed on the inner side of the circulation path of the fixing belt 31.

  The fixing belt 31 is a nonmagnetic endless belt including a conductive heat generating layer. Such a belt can be formed by, for example, a method of depositing a thin film of copper or aluminum, which is a nonmagnetic metal, on a belt base material made of a heat resistant resin such as polyimide. Further, a release layer may be provided on the surface. This release layer is for improving the releasability with the toner, and is made of, for example, PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) having a thickness of about 30 μm. In addition, for example, fluororubber, or fluororesin such as PTFE, FEP, and PFEP may be used.

The pressure belt 34 is an endless belt having a ferromagnetic layer (for example, a relative magnetic permeability of 1.02 or more). Examples of the material of the ferromagnetic layer include iron and nickel.
While the fixing belt 31 and the pressure belt 34 are not heated by electromagnetic induction, the surfaces of the belt portions 311 and 341 facing each other are in contact with each other or have a slight gap. As will be described later, this belt portion is a portion positioned at the fixing nip 38.

The driving rollers 32 and 35 are connected to a motor (not shown) and rotate by receiving the driving force of the motor. By this rotation, the fixing belt 31 and the pressure belt 34 are moved at substantially the same speed in the direction of the arrows in FIG. It is run around.
The magnetic flux generator 37 has an exciting coil 371 and a core 372 and is disposed to face the pressure belt 34 with the fixing belt 31 interposed therebetween. The exciting coil 371 is connected to the AC voltage output unit 51 and the DC voltage output unit 52, and a voltage in which the DC voltage from the DC voltage output unit 52 is superimposed on the AC voltage from the AC voltage output unit 51 is applied. Then, an alternating magnetic field is generated.

The core 372 mainly guides the magnetic flux generated by the alternating magnetic field generated from the exciting coil 371 to the belt portion 311 of the fixing belt 31.
Due to the magnetic flux guided to the fixing belt 31 through the core 372, an eddy current is generated in the conductive layer of the fixing belt 31, and the eddy current generates heat proportional to the skin resistance of the conductive layer. 31 itself is heated.

In parallel with the electromagnetic induction heating, the exciting coil 371 acts as an electromagnet due to the DC component included in the applied voltage, and an attractive force A is generated between the pressing belt 34 having a ferromagnetic layer. By this attractive force A, the belt portion 341 of the pressure belt 34 is mainly pulled toward the exciting coil 371 side.
As described above, an eddy current is generated in the fixing belt 31 due to the magnetic flux from the exciting coil 371, and most of the eddy current is generated in Joule heat. Therefore, the magnetic flux generated by the eddy current is generated in a direction (reverse direction) in which the magnetic flux from the exciting coil 371 is always canceled. The repulsive force B is generated between the exciting coil 371 and the fixing belt 31 by the magnetic fluxes generated in opposite directions.

A repulsive force B in the direction toward the pressure belt 34 acts on the belt portion 311 of the fixing belt 31, and an attractive force A in the direction toward the fixing belt 31 acts simultaneously on the belt portion 341 of the pressure belt 34. The fixing belt 31 and the pressure belt 34 are brought into pressure contact with each other by the action of the attractive force A and the repulsive force B, and the pressure contact portion constitutes the fixing nip 38.
The nip pressure at the fixing nip 38 (pressure contact force between the fixing belt 31 and the pressure belt 34) varies depending on the magnitudes of the attractive force A and the repulsive force B. Specifically, the attractive force A varies depending on the magnitude of the superimposed DC voltage, and the repulsive force B varies depending on the frequency and intensity of the alternating magnetic field. Here, the repulsive force B is usually not as great as the attractive force A, and there are some fluctuations depending on the degree of change in the magnetic flux density, but since it is a high-frequency magnetic field, it is considered to be averaged and maintained at a substantially constant magnitude. It is done. The nip pressure is varied to an optimum value depending on the type of the sheet S to be used in the DC voltage output control described later.

  In this way, the nip pressure is varied depending on the sheet type. For example, if the nip pressure is too low, the fixing rate decreases, and if the nip pressure is too high, wrinkles and curls are likely to occur. This is because it is easy to change depending on the strength or moisture content of thin paper or thick paper, and the fixing performance can be improved by using a nip pressure suitable for the sheet depending on the sheet type. The optimum nip pressure for each sheet type and the DC voltage value necessary for obtaining the nip pressure are obtained in advance by experiments, and information associating the sheet type with the voltage value is stored in the EEPROM 45 as applied DC voltage value information. The

FIG. 4 is a diagram illustrating an example of the content of applied DC voltage value information. As shown in the figure, DC voltage values V1 to V3 are set for three types of sheets, ie, thin paper, plain paper, and thick paper, respectively.
Returning to FIG. 3, when the superimposed voltage is applied to the exciting coil 371, the fixing belt 31 generates heat and the fixing nip 38 is secured. In this state, the sheet S on which an unfixed toner image is formed (transferred) is fixed. When passing through the nip 38, the toner image is fixed on the sheet S by being heated and pressurized in the fixing nip 38. Although not shown, a sensor for detecting the surface temperature of the fixing belt 31 is disposed, and the fixing belt 31 is maintained at a temperature (target temperature) suitable for fixing based on a detection signal from the sensor. Thus, the amount of power supplied to the exciting coil 371 is adjusted.

(4) DC Voltage Output Control Process FIG. 5 is a flowchart showing the contents of the DC voltage output control process. This DC voltage output control process is executed by the CPU 41.
As shown in the figure, first, it is determined whether or not the job has been started (step S1). If it is determined that the job is started (“YES” in step S1), the sheet type information of the sheet used in the job is acquired (step S2). This acquisition is performed as follows. That is, it is determined from which paper feed cassette the sheet used by the job is fed. Then, the sheet storage information stored in advance in the EEPROM 45 is referred to read out the sheet type associated with the determined sheet feeding cassette.

When the job start is determined, an AC voltage having a predetermined frequency is output from the AC voltage output unit 51. An AC voltage from the AC voltage output unit 51 is applied to the exciting coil 371 and heat generation of the fixing belt 31 is started. At this time, the DC voltage output unit 52 has not yet output a DC voltage.
Next, information indicating the value of the DC voltage to be applied to the exciting coil 371 is acquired (step S3). This acquisition is performed by referring to the applied DC voltage value information (FIG. 4) stored in the EEPROM 45. For example, when the sheet type information acquired in step S2 is information indicating thick paper, information indicating the voltage value V3 is acquired.

Then, it is determined whether or not the leading edge of the sheet being conveyed is detected by the job (step S4). This determination is made based on whether or not a leading edge detection signal from the sheet detection sensor 6 has been received.
When it is determined that the leading edge of the sheet is detected (“YES” in step S4), an internal timer (not shown) is started (step S5). It is determined whether or not a first predetermined time has elapsed from the start of counting by the internal timer (step S6). Here, the first predetermined time corresponds to the time required for the leading edge of the sheet S to reach the fixing nip 38 of the fixing unit 30 after the leading edge of the sheet is detected by the sheet detection sensor 6. For example, it is obtained in advance by dividing the distance L from the sheet leading edge detection position of the sheet detection sensor 6 on the conveyance path to the fixing nip 38 by the conveyance speed V.

  If it is determined that the first predetermined time has elapsed (“YES” in step S6), the DC voltage output unit 52 is instructed to apply a DC voltage having the same value as the DC voltage acquired in step S3 to the exciting coil 371. To output. As a result, a voltage in which the DC voltage output from the DC voltage output unit 52 is superimposed on the AC voltage output from the AC voltage output unit 51 is applied to the excitation coil 371, and the fixing belt 31 generates heat while the fixing belt 31 generates heat. A fixing nip 38 is secured between the pressure belt 34 and the pressure belt 34.

  Subsequently, it is determined whether or not a second predetermined time has elapsed from the start of counting by the internal timer (step S8). Here, the second predetermined time corresponds to a time required for the trailing edge of the sheet S to pass through the fixing nip 38 of the fixing unit 30 after the leading edge of the sheet is detected by the sheet detection sensor 6. For example, the distance L is obtained by dividing the value obtained by adding the sheet conveyance direction length L2 of the fixing nip 38 and the sheet conveyance direction length L3 of the sheet S by the conveyance speed V. The L3 is determined and acquired according to which of the sheet cassettes 21 to 23 the sheet S has been conveyed from.

  If it is determined that the second predetermined time has elapsed ("YES" in step S8), the internal timer is reset (step S9), and the DC voltage output unit 52 is instructed to stop applying the DC voltage (step S9). S10). As a result, the fixing nip 38 is released. By starting and stopping the output of the DC voltage at such timing, the DC voltage is applied to the exciting coil 371 only while the sheet S passes through the fixing nip 38 as shown in the schematic diagram of FIG. DC ON).

  Since the fixing nip 38 only needs to be secured when the sheet passes, the DC voltage is always applied if the fixing nip 38 is secured for each sheet according to the sheet conveyance timing as in the present embodiment. This contributes to power saving as compared with a configuration in which the fixing nip 38 is continuously secured by applying. In addition, if the nip pressure is constantly maintained, the belt may be deformed due to the tension over time. However, as in the present embodiment, the nip pressure is ensured only when necessary. Thus, the risk of such belt deformation can be reduced.

  Returning to FIG. 5, it is determined whether or not the job is finished (step S11). If the job is not completed (“NO” in step S11), the process returns to step S2, and acquisition of sheet type information for the next conveyed sheet S, acquisition of DC voltage for the sheet S, output of DC voltage, etc. Processing is executed (steps S2 to S10). Until it is determined that the job is finished, the processes in steps S2 to S10 are repeatedly executed. When it is determined that the job is finished (“YES” in step S11), the DC voltage output control is finished.

  As described above, in the present embodiment, the fixing nip 38 is secured by superimposing the DC voltage on the AC voltage to the exciting coil 371, so that it is not necessary to use a pressing member such as a pad, and the pressing member When this is used, the life of the belt is not shortened due to wear of the belt. In addition, since the life of the fixing belt 31 and the like can be extended, labor and cost for replacing the fixing belt and the like can be reduced as compared with the conventional case. Furthermore, since no pressing member is used, the heat of the fixing belt 31 is not directly transmitted to the pressing member and escapes, and the warm-up time can be shortened accordingly.

  In the above description, the DC voltage application control is performed in units of sheets. However, the present invention is not limited to this. For example, as shown in the schematic diagram of FIG. 6B, the control may be performed in units of the region 7 of the formed image on the sheet. . Specifically, application of a DC voltage is started immediately before the leading edge of the formed image in the sheet conveying direction of the region 7 enters the fixing nip 38, and the DC voltage is applied immediately after the trailing edge of the formed image passes the fixing nip 38. Control to stop the application of.

  The position of the formed image on the sheet is obtained as follows. For example, before executing the job, the image data is bitmap-developed in the image memory 46, a known image area is determined with reference to the expanded data, and a coordinate value in one page of the determined image area is obtained. . Information that associates the coordinate values in the memory with the actual coordinate values on the sheet may be held, and the obtained coordinate values may be converted into coordinate values on the sheet. If the coordinate value of the formed image on the sheet is known, the time t required from the detection of the leading edge of the sheet by the sheet detection sensor 6 until the leading edge of the image on the sheet reaches the fixing nip 38 can be calculated.

If the application of the DC voltage is started at the elapse of time t from the detection of the sheet leading edge during the job execution, the fixing nip 38 is ensured just in time with the timing at which the leading edge of the formed image reaches the fixing unit 30. Become. The fact that the trailing edge of the image on the sheet has passed through the fixing nip 38 can also be detected in the same manner as the leading edge of the image.
Compared to the configuration in which the start and stop of the DC voltage are controlled in units of sheets, the processing such as determination of the image area is increased. However, power is applied to the excitation coil 371 only while the image portion on the sheet passes through the fixing nip 38. Since it is supplied, time for energizing the blank portion becomes unnecessary, and further power saving can be achieved.

In the above description, the AC voltage is controlled to be applied to the exciting coil 371 to maintain the fixing belt 31 at the target temperature regardless of whether or not the sheet reaches the fixing nip 38 during execution of the job. However, it is not limited to this. For example, the output start and stop of the AC voltage may be controlled in the same manner as the DC voltage.
The present invention is not limited to the fixing device and the image forming apparatus, and may be a method for ensuring the nip pressure in the fixing nip. Furthermore, the method may be a program executed by a computer. The program according to the present invention includes, for example, a magnetic disk such as a magnetic tape and a flexible disk, an optical recording medium such as a DVD-ROM, DVD-RAM, CD-ROM, CD-R, MO, and PD, and a flash memory recording medium. It can be recorded on various computer-readable recording media, and may be produced, transferred, etc. in the form of the recording medium, wired and wireless various networks including the Internet in the form of programs, In some cases, the data is transmitted and supplied via broadcasting, telecommunication lines, satellite communications, or the like.

<Modification>
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications can be implemented.
(1) In the above embodiment, the configuration example in which the fixing belt 31 is used as the first rotating body and the pressure belt 34 is used as the second rotating body has been described. However, both rotating bodies are not limited to the belt. . For example, as shown in FIG. 7, one can be a roller and the other a belt.

FIG. 7 shows an example in which a fixing roller 61 is used instead of the fixing belt as the heating rotator. The fixing roller 61 is a cylindrical roller made of a non-magnetic conductor, and a magnetic flux generation unit 37 made up of an excitation coil 371 and a core 372 is provided inside the fixing roller 61.
The pressure belt 64 is stretched between the driving roller 65 and the driven roller 66, and the belt portion located between the two rollers is pressed against the peripheral surface of the fixing roller 61, so that the pressure belt 64 is interposed between the fixing roller 61 and the pressure belt 64. A fixing nip 38 is secured. In the case of this example, a certain amount of nip pressure is generated before the application of the DC voltage. The reason why the nip pressure is generated in this manner is to secure the length necessary for fixing in the sheet conveying direction of the fixing nip 38. The point that the pressure belt 64 is an endless belt having a ferromagnetic layer is the same as the above embodiment.

In such a configuration, by applying a superimposed voltage to the exciting coil 371, an attractive force A is generated between the pressure belt 64 and the exciting coil 371, and the same effect as in the embodiment can be obtained.
In the case of the configuration shown in FIG. 7, regardless of the attractive force A due to the DC voltage, as the thickness of the sheet S increases, the restoring force of the pressure belt 64 toward the fixing roller 61 increases in the fixing nip 38. The nip pressure is also increased. That is, if thick paper is used, the nip pressure is higher than that of thin paper by the difference in thickness. If the magnitude of the attractive force A is changed in consideration of the nip pressure changing depending on the sheet thickness in this way, a nip pressure suitable for the sheet can be obtained.

FIG. 8 is an example in which the magnitude of the attractive force A is varied between thin paper and thick paper. FIG. 8A shows a case where thin paper is used, and FIG. 8B shows a case where thick paper is used. Show.
As shown in both figures, it can be seen that the magnitude of the attractive force A is smaller in the thick paper than in the thin paper. Since the attractive force A is smaller in the thick paper than in the thin paper, the magnitude of the DC voltage can be reduced accordingly, and power can be saved. The DC voltage corresponding to each attractive force A is obtained and stored in advance, and the DC voltage set for the sheet (thin paper and thick paper) used at the time of job execution is supplied to the exciting coil 371. The

(2) In the embodiment and the modification example (1), the configuration example in which the drive voltage in which the DC voltage is superimposed on the AC voltage is applied to one excitation coil 371 is not limited to this. It is possible to adopt a configuration in which excitation coils for voltage and DC voltage are provided separately.
FIG. 9 is a diagram illustrating a configuration example of the magnetic flux generation unit 70 according to the modification (2).
As shown in the figure, the magnetic flux generator 70 includes an excitation coil 71 for AC voltage and an excitation coil 72 for DC voltage as excitation coils.

As shown in the enlarged view of FIG. 10, for example, a litz wire formed by twisting fine wires 711 is used for the exciting coil 71. Thus, by using a litz wire, the coil surface area can be increased, and an alternating current can be made to flow more easily by the skin effect.
On the other hand, the exciting coil 72 uses a line having a large cross-sectional area as shown in FIG. This is because a direct current flows more easily when the cross-sectional area is made larger and the electric resistance is made smaller than when the surface area is increased. By using a wire having a large cross-sectional area, the ratio of the area of the portion 721 where the current does not flow, such as a coil film, becomes smaller than that of the litz wire, so the resistance to direct current is reduced and the nip pressure is generated efficiently. Can do. Although the configuration example using the fixing roller 61 and the pressure belt 64 has been described with reference to FIG. 9, both can be applied to the configuration of the belt as in the embodiment, for example.

(3) In the above description, the pressure belt 64 is stretched using two rollers, but the present invention is not limited to this. It is also possible to adopt a configuration in which it is stretched by three or more rollers. The same applies to the fixing belt.
(4) In the above embodiment and modification, the magnet means is configured to apply a DC voltage to the exciting coil to act as an electromagnet. However, the magnet means attracts the pressure belt 34 toward the fixing belt 31 side. Any configuration that can generate the attractive force A is not limited to a configuration that uses an exciting coil.

For example, a permanent magnet can be used. For example, the permanent magnet may be located inside the circulation path of the fixing belt 31 and at a position where a magnetic force can be applied to the nip portion. In this case, since electric power (DC voltage) is not required to generate the attractive force A, there is an effect of suppressing power consumption.
However, in this case, it is difficult to control the nip pressure as compared with the first embodiment and the first to sixth modifications.

  (5) In the above embodiment, the example in which the fixing device and the image forming apparatus according to the present invention are applied to a monochrome copying machine has been described. However, the present invention is not limited to this. Regardless of color or monochrome image formation, the first and second rotating bodies are pressed to secure a fixing nip, and the first rotating body is induction-heated by the magnetic flux generated from the exciting coil, thereby unfixed images. The fixing device that passes the formed sheet through the fixing nip and thermally fixes the unfixed image and the image forming apparatus including the fixing device can be applied to, for example, a printer, a FAX, an MFP (Multiple Function Peripheral), and the like.

  The contents of the above embodiment and the above modification may be combined.

  The fixing device of the present invention in an image forming apparatus has good heat generation efficiency, and is useful as a technique for realizing resource saving and cost reduction.

1 is a diagram illustrating a schematic configuration of a copier according to a first embodiment. 2 is a block diagram illustrating a configuration of a control unit of a copying machine. FIG. FIG. 3 is a diagram illustrating a configuration of an induction heating type fixing unit of a copying machine. It is a figure which shows the example of the content of applied DC voltage value information. It is a flowchart which shows the content of DC voltage output control. It is the figure which showed typically the output timing of the DC voltage by DC voltage output control. 10 is a diagram illustrating a configuration example of a fixing unit according to Modification 1. FIG. FIG. 10 is a diagram illustrating a state in which a sheet passes through a fixing unit according to Modification 1. 10 is a diagram illustrating a configuration example of a fixing unit according to Modification 2. FIG. FIG. 9 is a diagram illustrating an example of an enlarged cross section of an exciting coil of a fixing unit according to Modification 2. It is a figure which shows schematic structure of the fixing part of the conventional induction heating system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Copier 30 Fixing part 31 Fixing belt 32, 35, 65 Driving roller 33, 36, 66 Driven roller 34, 64 Pressing belt 37, 70 Magnetic flux generation part 38 Fixing nip 40 Control part 51 AC voltage output part 52 DC voltage output Unit 61 Fixing roller 71 Excitation coil 72 for AC voltage Excitation coil 371 for DC voltage Excitation coil 372 Core A Attraction B Repulsion S Sheet

Claims (9)

A fixing nip is formed by pressing the peripheral surface of the second rotating body on the peripheral surface of the first rotating body, and the first rotating body is induction-heated by the magnetic flux generated by the exciting coil, thereby A fixing device for passing the formed sheet through the fixing nip and thermally fixing the unfixed image,
The second rotating body is composed of an endless belt including a ferromagnetic layer stretched by two or more rollers, and is located in the fixing nip among the belts constituting the second rotating body. Magnetic means is applied to the portion to generate an attractive force in the fixing nip direction, and includes a magnet means for ensuring a nip pressure ,
The magnet means includes a magnet coil and a DC voltage applying means for applying a DC voltage thereto,
The fixing device, wherein the exciting coil and the magnet coil are wound at the same position . A fixing nip is formed by pressing the peripheral surface of the second rotating body on the peripheral surface of the first rotating body, and the first rotating body is induction-heated by the magnetic flux generated by the exciting coil, thereby A fixing device for passing the formed sheet through the fixing nip and thermally fixing the unfixed image,
The second rotating body is composed of an endless belt including a ferromagnetic layer stretched by two or more rollers, and is located in the fixing nip among the belts constituting the second rotating body. Magnetic means is applied to the portion to generate an attractive force in the fixing nip direction, and includes a magnet means for ensuring a nip pressure,
The magnet means includes a magnet coil and a DC voltage applying means for applying a DC voltage thereto,
A fixing device in which the exciting coil is used also as a magnet coil by superimposing a DC voltage output from the DC voltage applying means on an AC voltage applied to the exciting coil. .   3. The fixing according to claim 1, wherein the first rotating body is formed of an endless belt that does not include a ferromagnetic material and is stretched between two or more other rollers. apparatus. The first rotating body is a hollow roller, coil the magnet is characterized by being arranged at a position opposed to the fixing nip of the hollow portion of the roller, claims 1 to 3 The fixing device according to any one of the above. The fixing device according to claim 1, wherein the exciting coil is formed by winding a litz wire, and the magnet coil is formed by winding a single wire. A sheet thickness acquisition means for acquiring information on the thickness of the sheet passing through the fixing nip;
6. The fixing device according to claim 1, wherein the DC voltage applying unit applies a DC voltage having a different value depending on the thickness of the acquired sheet. A sheet passing timing acquisition unit that acquires a timing at which the sheet passes the position of the fixing nip;
The fixing device according to claim 1, wherein the voltage applying unit applies a DC voltage to the magnet coil when the sheet passes through the fixing nip. A sheet passing timing acquisition means for acquiring a timing at which a toner image formed on a sheet to be a fixing counter image passes through a fixing nip position;
Said voltage applying means, and applying a DC voltage to the coil magnet when the toner image on the sheet passing through the fixing nip, the fixing according to any one of claims 1 7 apparatus. An image forming apparatus comprising the fixing device according to claim 1 .

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