JP4760688B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device that heats and melts an unfixed toner image formed on a recording medium such as recording paper in an image forming apparatus such as a copying machine or a printer, and in particular, guides it as a heat source. The present invention relates to a fixing device using a heating type heat source. The present invention also relates to an image forming apparatus provided with the fixing device.

  A fixing device employed in an electrophotographic image forming apparatus is usually a fixing rotating body such as a rotatable fixing roller, and a pressure such as a rotatable pressure roller pressed against the fixing rotating body. A recording medium comprising a rotator and a heat source for heating the fixing rotator, wherein the fixing rotator is heated by the heat source, and a toner image is held in a nip portion between the fixing rotator and the pressure rotator. , The toner image is melted and fixed on the recording medium under pressure.

  As such a heat source, a heating element (such as a heater) provided on the inner surface or the outer peripheral surface of the fixing rotator has been adopted. However, due to today's demand for energy saving, an electromagnetic induction heating method that achieves high heat conversion efficiency. The heat source is attracting attention. For example, Japanese Patent No. 2616433 discloses a fixing device that generates a magnetic flux by energizing a coil formed in a spiral pattern on a support, and uses a generated magnetic flux to heat a metal heat roller used as a fixing roller by electromagnetic induction. Is disclosed.

  Recently, heat conversion efficiency equal to or higher than that of a conventional heat rotator type fixing device using a halogen lamp heater has been obtained, and the rise to the fixing temperature for fixing a toner image is quick, and the fixing device is compact. As a fixing device that can be realized, a fixing device having a configuration in which a magnetic flux generated by energizing a coil is guided to an electromagnetic induction heat generating layer provided on a fixing rotating body using a core material such as a ferrite core has been proposed.

  For example, a rotatable fixing rotating body having an electromagnetic induction heat generating layer, a rotatable pressure rotating body pressed against the fixing rotating body, and an electromagnetic induction heat generating layer of the fixing rotating body are caused to generate electromagnetic induction heat. There is a fixing device that heats the fixing rotator by causing the electromagnetic induction heat generation layer of the fixing rotator to generate heat by the magnetic flux generated by the magnetic flux generator.

In addition, for this type of fixing device, a fixing device in which the heat capacity of the heat generating layer is reduced by reducing the thickness of the electromagnetic induction heat generating layer has been proposed in order to further improve the thermal efficiency and speed up to the fixing temperature. (For example, refer to JP-A-2005-351929 and JP-A-2005-351931).
According to the electromagnetic induction heating type fixing device, the electromagnetic induction heat generating layer in the fixing rotating body can be directly heated, so that the heat capacity of the heat generating layer is smaller than that of a heat source conventionally used in the fixing device such as a halogen lamp heater. Even if it is reduced, the fixing rotator can be heated to the fixing temperature.

Japanese Patent No. 2616433 JP 2005-351929 A JP 2005-351931 A

  However, in a fixing device for fixing a toner image to a recording medium by passing a recording medium holding a toner image through a nip portion between a heated fixing rotator and a pressure rotator pressed against the fixing rotator, the recording medium is fixed. When passing through the nip portion between the rotating body and the pressure rotating body, the heat of the fixing rotating body is taken away by the recording medium and the fixing rotating body temperature decreases.

  The surface temperature of the fixing rotator such as the fixing roller is controlled based on the temperature detected by a temperature sensor provided in contact with or non-contact with the fixing rotator. Separating means (for example, a recording medium separating claw) for separating the recording medium from the fixing rotator is provided on the outlet side of the nip portion between the pressure rotators, and a temperature sensor is disposed on the nip portion outlet side. Therefore, the temperature sensor is generally arranged on the inlet side of the nip portion.

  As described above, in the fixing device in which the temperature sensor is arranged on the inlet side of the nip portion, when the temperature of the fixing rotating body is lowered by passing the recording medium through the nip portion as described above, the temperature drop is caused by the fixing at which the leading end of the recording medium has reached. The part of the rotating body arrives at the temperature sensor due to the rotation of the fixing rotating body, and even if a temperature drop is detected by the temperature sensor, there is a response delay in the temperature increase control of the fixing rotating body. Therefore, the fixing rotator portion that has not been sufficiently heated up proceeds to the nip portion as it is.

When such a situation occurs, for the recording medium whose recording medium conveyance direction length is larger than the fixing rotator circumferential length, the toner image is fixed at a lower temperature than the medium area where the toner image is fixed at a predetermined fixing temperature. Therefore, a large level difference in image gloss occurs between the two areas, and the image quality deteriorates.
In addition, for a recording medium whose length in the conveyance direction of the recording medium is equal to or less than the circumference of the fixing rotator, when a toner image is sequentially placed on a plurality of recording media, the image is recorded between the preceding recording medium and the succeeding recording medium. Gloss steps may occur. Note that the gloss level difference in this case is a difference in the gloss level between the preceding and following recording media, and such a case is also referred to as a gloss level difference in this specification. This also reduces the image quality.

  Such a gloss step is particularly thin when the heat capacity of the fixing rotator is small, for example, in the electromagnetic induction heating type fixing device described above, the electromagnetic induction heating layer of the fixing rotator seeks a rapid rise to the fixing temperature. In the case of a low heat capacity or in an electromagnetic induction heating type fixing device, a drive circuit (for example, a high-frequency inverter) in which power input to a magnetic flux generator tends to be delayed without responding quickly to temperature information detected from a temperature sensor This is likely to occur when the drive circuit is used.

  Accordingly, the present invention provides a rotatable fixing rotator having an electromagnetic induction heating layer, a rotatable pressure rotator pressed against the fixing rotator, and generation of magnetic flux that generates heat from the electromagnetic induction heating layer of the fixing rotator. An electromagnetic induction heating layer of the fixing rotator by the magnetic flux generator and passing a recording medium holding a toner image in a nip portion between the fixing rotator and the pressure rotator. A fixing device for fixing the toner image to the recording medium, wherein the toner image fixed image does not cause a gloss level difference, or even if it occurs, the level can be suppressed to a level that can be ignored in practical use, and the toner has good quality. It is a first object to provide a fixing device capable of obtaining an image-fixed image.

  According to the present invention, an electrostatic latent image corresponding to an image to be formed is formed on an image carrier, the electrostatic latent image is developed into a toner image, and the toner image is fixed to a recording medium by a fixing device. In the image forming apparatus, a toner image fixed image does not cause a gloss level difference, or even if it occurs, the level can be suppressed to a level that can be practically ignored, and a toner image fixed image with good quality can be obtained. It is a second problem to provide an image forming apparatus.

In order to solve the first problem, the present invention provides:
A rotatable fixing rotator having an electromagnetic induction heat generating layer, a rotatable pressure rotating body pressed against the fixing rotator, and a magnetic flux generator for generating heat from the electromagnetic induction heat generating layer of the fixing rotator, The magnetic flux generating device generates heat in the electromagnetic induction heat generating layer of the fixing rotator, and the recording medium holding the toner image is passed through the nip portion between the fixing rotator and the pressure rotator, thereby causing the toner image to pass through the recording medium. A fixing device for fixing on a recording medium;
A temperature sensor for detecting a surface temperature of the fixing rotator on the inlet side of the nip portion;
A controller that controls the drive circuit of the magnetic flux generator so that the surface temperature of the fixing rotator is set to a predetermined toner image fixing temperature based on the temperature detected by the temperature sensor;
The control unit is configured to fix the toner image on the recording medium even when the driving circuit of the magnetic flux generator is being controlled so that the surface temperature of the fixing rotator is directed to the fixing temperature. The fixing rotor peripheral surface area having a predetermined length in the circumferential direction of the fixing rotator opposite to the rotation direction of the fixing rotator from the portion on the fixing rotator reached by the magnetic flux generator is a fixing rotator heating area by the magnetic flux generator. A fixing device is provided that controls the drive circuit so that a predetermined constant power is supplied to the magnetic flux generator during a period from entering to exiting.

  Here, “predetermined constant power input to the magnetic flux generator” means that when the length of the recording medium in the transport direction is longer than the circumference of the fixing rotator, the fixing rotation in the transport direction from the leading end of the recording medium in the transport direction Power for suppressing the occurrence of a gloss level difference between the area corresponding to one circumference of the body and the subsequent area. When the length of the recording medium in the conveyance direction is equal to or less than the circumference of the fixing rotating body, the preceding recording This is power for suppressing the occurrence of a gloss level difference between the medium and the subsequent recording medium.

  According to the fixing device of the present invention, in fixing the toner image onto the recording medium, basically, the surface of the fixing rotator is determined based on the temperature detected by the temperature sensor on the surface of the fixing rotator under the instruction of the control unit. The drive circuit of the magnetic flux generator is controlled so that the temperature goes to a predetermined toner image fixing temperature, whereby the surface temperature of the fixing rotator is directed to the toner image fixing temperature.

  However, even during this control, the control unit fixes a fixed length of a predetermined length in the circumferential direction of the fixing rotator opposite to the rotation direction of the fixing rotator from the portion on the fixing rotator where the leading edge of the recording medium has reached. The drive circuit is controlled so that a predetermined constant power is applied to the magnetic flux generator during a period from when the rotating body peripheral surface area enters the fixing rotary body heating region by the magnetic flux generator until it comes out.

  Due to the constant power supply to this magnetic flux generator, the surface area of the fixing rotating body whose temperature has decreased due to the entry of the recording medium into the nip between the fixing rotating body and the pressure rotating body arrives at the nip again. Thus, the temperature rise is started, and thus a gloss level difference is not generated on the toner image fixed image formed on the recording medium, or even if it occurs, the level can be suppressed to a level that can be ignored practically, and the high quality toner. An image-fixed image can be obtained.

  As the “constant power” input to the magnetic flux generator to suppress the occurrence of the gloss level difference, the amount of heat taken from the fixing rotator to the recording medium is compensated, and the surface temperature of the fixing rotator is directed to a fixing temperature suitable for toner image fixing. For example, when the toner images are sequentially fixed on two or more recording media without applying the constant power, based on the temperature detected by the temperature sensor. The average power of the electric power supplied from the drive circuit to the magnetic flux generator under the instruction of the control unit so that the fixing rotator moves toward the fixing temperature can be given.

Moreover, the following period can be mentioned as said "period" which inputs the predetermined fixed electric power to the said magnetic flux generator. That is, the period is
(1) The length of one rotation of the fixing rotator in the circumferential direction of the fixing rotator opposite to the rotation direction of the fixing rotator from the portion on the fixing rotator at which the leading end of the recording medium reaches
(2) In the circumferential direction of the fixing rotator from the part on the fixing rotator where the leading edge of the recording medium reaches to the part on the fixing rotator where the trailing edge of the recording medium reaches Is a period from when the fixing rotor peripheral surface area of the shorter one of the two lengths enters the fixing rotor heating area by the magnetic flux generator until it exits. When both the lengths are the same, it is a period from when the fixing rotator peripheral surface area having a length corresponding to one rotation of the fixing rotator enters the fixing rotator heating area to exit.

Here, “the length of one rotation of the fixing rotator in the circumferential direction of the fixing rotator opposite to the rotation direction of the fixing rotator from the portion on the fixing rotator where the leading edge of the recording medium reaches” (1) is
When the conveyance direction length of the recording medium is longer than the circumferential length of the fixing rotator, the above-mentioned (2) `` on the fixing rotator reached by the rear end of the recording medium from the part on the fixing rotator reached by the recording medium front end The length of the circumferential direction of the fixing rotator reaching the opposite direction to the direction of rotation of the fixing rotator to
When the length of the recording medium in the conveyance direction is shorter than the circumference of the fixing rotator, it becomes longer than the length (2).
When the conveyance direction length of the recording medium is the same as the circumference of the fixing rotator, both are the same.

Therefore, the “period” for suppressing the occurrence of the gloss level difference is
When the conveyance direction length of the recording medium is equal to or longer than the circumferential length of the fixing rotator, the circumferential surface area of the fixing rotator having a length corresponding to one rotation of the fixing rotator in (1) is the fixing rotator heating. It is the period from entering the area to leaving,
When the conveyance direction length of the recording medium is shorter than the circumferential length of the fixing rotator, the period of the peripheral surface of the fixing rotator having the length of (2) above is the period from entering the fixing rotator heating area to exiting. .

In any case, examples of the fixing rotator include a rotatable fixing roller and an endless fixing belt. The pressure rotator may be a rotatable pressure roller or an endless pressure belt.
In any case, the control unit may switch a constant power input to the magnetic flux generator according to a recording medium type (plain paper, overhead projector recording medium, etc.). Accordingly, it is possible to cope with a change in the amount of heat taken from the fixing rotating body depending on the recording medium type.

  In order to solve the second problem, the present invention forms an electrostatic latent image corresponding to an image to be formed on an image carrier, develops the electrostatic latent image into a toner image, There is also provided an image forming apparatus for fixing the toner image to a recording medium with a fixing device, wherein the fixing device according to the present invention is used as the fixing device.

Since the image forming apparatus according to the present invention includes the fixing device according to the present invention as the fixing device, it is possible to form a good toner image fixed image in which the occurrence of image gloss difference is suppressed.
The image forming apparatus according to the present invention may form a monochrome image or a color image.

In the case of a monochrome image forming apparatus, the toner image formed on the electrostatic latent image carrier is transferred to a recording medium directly or via an intermediate transfer body and fixed by a fixing device.
In a color image forming apparatus, generally, a toner image formed on an electrostatic latent image carrier is once transferred to an intermediate transfer member, transferred from the intermediate transfer member to a recording medium, and fixed by a fixing device.
In any case, the toner image formed on the electrostatic latent image carrier is transferred to a recording medium and fixed by a fixing device.

  As described above, according to the present invention, a rotatable fixing rotator having an electromagnetic induction heating layer, a rotatable pressure rotator pressed against the fixing rotator, and an electromagnetic induction heating layer of the fixing rotator. And a magnetic flux generating device that heats the electromagnetic induction heat generating layer of the fixing rotator by the magnetic flux generator and holds a toner image in a nip portion between the fixing rotator and the pressure rotator. A fixing device that fixes the toner image to the recording medium by passing the toner image, and does not cause a gloss level difference on the toner image fixed image, or even if it occurs, the degree can be suppressed to a level that can be ignored in practice, Thus, it is possible to provide a fixing device capable of obtaining a toner image fixed image with good quality.

  According to the invention, an electrostatic latent image corresponding to the image to be formed is formed on the image carrier, the electrostatic latent image is developed into a toner image, and the toner image is applied to a recording medium by a fixing device. An image forming apparatus for fixing, in which no gloss level difference is generated in a toner image fixed image, or even if it occurs, the level can be suppressed to a level that can be practically ignored, and a toner image fixed image with good quality can be obtained. An image forming apparatus that can be provided can be provided.

Embodiments of the present invention will be described with reference to the drawings.
[1] Image forming apparatus (see FIG. 1)
FIG. 1 shows an example of an image forming apparatus provided with an example of a fixing device according to the present invention. The image forming apparatus in FIG. 1 is a tandem color printer A that can form a color image.
The color printer A includes a drive roller 31 and an endless intermediate transfer belt 4 that is wound around a roller 32 facing the drive roller 31. The transfer belt 4 can be rotated counterclockwise in the figure (arrow direction in the figure) by a driving roller 31 driven by a belt drive unit (not shown).

  A cleaner 40 for cleaning secondary transfer residual toner and the like on the transfer belt 4 faces the transfer belt portion on the facing roller 32. The secondary transfer roller 5 faces the transfer belt portion on the driving roller 31.

  The surface layer portion of the secondary transfer roller 5 is formed of an elastic material, and is pressed against the intermediate transfer belt 4 by a pressing unit (not shown) to form a nip portion between the intermediate transfer belt 4 and the intermediate transfer belt 4. , Or following the movement of the recording medium P fed into the nip as will be described later. A secondary transfer bias can be applied to the secondary transfer roller 5 from a secondary transfer bias power supply device (not shown).

A timing roller 7 is disposed below the secondary transfer roller 5, and a recording medium storage cassette 8 that stores a recording medium is further disposed below the timing roller 7.
A fixing device 6 is disposed above the transfer roller 5. The fixing device 6 is an example of a fixing device according to the present invention. The fixing device 6 will be described in detail later.

The recording medium P stored in the recording medium storage cassette 8 can be pulled out one by one by the medium supply roller 81 and supplied to the timing roller 7.
Examples of the recording medium P include recording paper and overhead projector sheets.

  Between the rollers 31 and 32 around which the intermediate transfer belt 4 is wound, the yellow image forming unit Y, the magenta image forming unit M, the cyan image forming unit C, and the rollers 32 to 31 are arranged along the transfer belt 4. Black image forming portions K are arranged in this order.

  Each of the image forming units Y, M, C, and K includes a drum-type photoconductor 11 as an electrostatic latent image carrier, and a charging device 12, an image exposure device 13, and a developing device 14 are provided around the photoconductor. The primary transfer roller 2, the cleaning device 15 for removing and cleaning the primary transfer residual toner on the photosensitive member, and the like are arranged in this order.

The photoreceptor 11, the charging device 12, the developing device 14, and the cleaning device 15 in each image forming unit are provided in a cartridge case, and form a process cartridge together with the cartridge case. That is, the yellow process cartridge YC for forming the yellow image forming portion Y, the magenta process cartridge MC for forming the magenta image forming portion M, the cyan process cartridge CC for forming the cyan image forming portion C, and the black image forming This is a black process cartridge KC for forming the portion K.
Each process cartridge is detachable from the printer body.

The primary transfer roller 2 is opposed to the photoconductor 11 with the transfer belt 4 in between, and rotates as the belt travels. A primary transfer bias for primary transfer of the toner image formed on the photoreceptor 11 to the belt 4 can be applied to the primary transfer roller 2 from a primary transfer bias power supply device (not shown).
The exposure device 13 performs image exposure on the photoconductor 11 using a laser beam in accordance with image information provided from a personal computer (not shown) or the like.

The photoconductor 11 in each image forming unit is a negatively chargeable photoconductor here, and can be driven to rotate clockwise in the drawing by a photoconductor drive motor (not shown).
A charging voltage can be applied to the charging device 12 in each image forming unit at a predetermined timing from a charging power supply device (not shown).

  The developing device 14 in each image forming unit employs a negatively chargeable toner in this example, and an electrostatic latent image formed on the photoconductor 11 is transferred from a developing bias applying power supply device (not shown) to a developing bias voltage. Can be reversely developed by the developing roller 141 to which is applied.

  Between the black image forming portion K and the driving roller 31 of the belt 4, an AIDC (image density) sensor 100 that also serves as a registration sensor is disposed. Information from the sensor 100 is input to a control unit Cont, which will be described later, and the control unit obtains an interval between patterns of each color formed on the intermediate transfer belt 4 according to the input information, and the interval is determined in advance. By comparing with the reference value, the writing start timing of each color image is adjusted.

According to the printer A, an image can be formed using one or more of Y, M, C, and K image forming units.
Taking a case where a full color image is formed using all of the image forming portions Y, M, C, and K as an example, first, a yellow toner image is formed in the yellow image forming portion Y, and this is formed on the transfer belt 4 as a primary. Transcript.

  That is, in the yellow image forming unit Y, the photosensitive member 11 is rotationally driven in the clockwise direction in the drawing, and the image exposure device is applied to the charged area of the photosensitive member 11 whose surface is uniformly charged to a predetermined potential by the charging device 12. 13, yellow image exposure is performed, and a yellow electrostatic latent image is formed on the photoreceptor 11. This electrostatic latent image is developed by a developing roller 141 to which a developing bias of a developing device 14 having yellow toner is applied to become a visible yellow toner image, and the toner image is transferred onto the transfer belt 4 by the primary transfer roller 2. Primary transfer is performed. At this time, a primary transfer bias voltage is applied to the primary transfer roller 2 from a power supply device (not shown).

  Similarly, a magenta toner image is formed in the magenta image forming unit M and transferred to the transfer belt 4, a cyan toner image is formed in the cyan image forming unit C and transferred to the transfer belt 4, and in the black image forming unit K. A black toner image is formed and transferred to the transfer belt 4.

  Yellow, magenta, cyan, and black toner images are formed at the timing when these toner images are transferred onto the intermediate transfer belt 4 in an overlapping manner. The multiple toner images formed on the transfer belt 4 are moved toward the secondary transfer roller 5 by the rotation of the transfer belt 4.

  On the other hand, the recording medium P is pulled out from the recording medium storage cassette 8 by the medium supply roller 81 and supplied to the timing roller 7 and is on standby.

  The recording medium P waiting at the timing roller 7 is supplied to the nip portion between the transfer belt 4 and the secondary transfer roller 5 in accordance with the multiple toner image sent by the intermediate transfer belt 4. Starts to convey the recording medium P, and is sent to the nip portion, and the multiple toner images are transferred onto the recording medium P by the secondary transfer roller 5 to which a secondary transfer bias is applied from a power supply device (not shown). Next transferred.

  Thereafter, the recording medium P is passed through the fixing device 6 where the multiple toner images are fixed on the recording medium P under heat and pressure. The recording medium P continues to be discharged to the discharge tray 9 by the discharge roller 91. Transfer residual toner or the like remaining on the intermediate transfer belt 4 is removed and cleaned by a cleaner 40, and transfer residual toner or the like remaining on the photoreceptor 11 in each image forming unit is removed and cleaned by a cleaning device 15.

[2] Fixing device 6 (see FIG. 2 etc.)
(2-1) Overall Configuration and Operation of Fixing Device 6 FIG. 2 is a cross-sectional view of the fixing device 6.
The fixing device 6 includes a fixing roller 61, a pressure roller 62 pressed against the fixing roller 61, and a magnetic flux generator 60 facing the fixing roller 61.

  The fixing roller 61 and the pressure roller 62 are arranged in parallel, and each roller is rotatably supported by a bearing member (not shown) at both ends. The pressure roller 62 is pressed against the fixing roller 61 under a predetermined pressure by a pressing device including a pressing spring (not shown), and forms a pressure nip portion (fixing nip portion) N together with the fixing roller 61. A temperature sensor SE for detecting the surface temperature of the fixing roller is disposed on the inlet side of the nip portion N in the conveyance direction of the recording medium P, which will be described later, and the recording medium P is separated from the fixing roller 61 on the outlet side. The separation claw 68 is disposed.

  The pressure roller 62 is rotationally driven at a predetermined peripheral speed in a clockwise direction indicated by an arrow in FIG. The fixing roller 61 is rotated by the rotation of the pressure roller 62 by the pressure friction force with the pressure roller 62 at the pressure nip N or by the pressure friction force with the recording medium P being nipped and conveyed at the nip N. To do. Alternatively, the pressure roller 62 may be driven to rotate by driving the fixing roller 61.

  The fixing roller 61 is heated by an electromagnetic induction heating method in which an electromagnetic induction heating layer 613 provided on the fixing roller 61 is heated by a magnetic flux generated by the magnetic flux generator 60. According to this heating method, the heat generating layer 613 with a low heat capacity in the fixing roller 61 can generate heat with high efficiency, and it is necessary to raise the temperature of the surface of the fixing roller to a temperature suitable for toner image fixing when the fixing device 6 is started. Time can be shortened.

  After the pressure roller 62 and the fixing roller 61 start to rotate, the induction heat generation layer 613 of the fixing roller 61 is heated by electromagnetic induction by the action of the magnetic flux generated by the magnetic flux generator 60, and the surface of the fixing roller 61 is heated. At this time, automatic temperature control is performed so that the surface temperature of at least the recording medium passage area of the fixing roller 61 becomes a temperature suitable for toner image fixing based on the temperature detected by the temperature sensor SE. The automatic temperature control will be described later with reference to FIG.

  In the toner image fixing process, when the surface temperature of at least the recording medium passage area of the fixing roller 61 is controlled to a temperature suitable for toner image fixing, the toner image is fixed from the nip portion between the secondary transfer roller 5 and the transfer belt 4. The recording medium P holding the unfixed toner image Pt that has come out is fed into the nip portion N between the fixing roller 61 and the pressure roller 62. At this time, the unfixed toner image carrying surface of the recording medium P faces the fixing roller 61.

  The recording medium P supplied to the pressure nip N between the fixing roller 61 and the pressure roller 62 is nipped and conveyed to the pressure nip N and heated by the fixing roller 61 so that the unfixed toner image Pt is added to the recording medium P. It is melt-fixed under pressure. The recording medium P that has passed through the pressure nip N is left as it is or separated from the fixing roller 62 by the separation claw 68, and is discharged to the discharge tray 9 by the discharge roller 91.

(2-2) Regarding the fixing roller 61 (see FIG. 2)
The fixing roller 61 may be composed of at least four layers of a support layer 611, a heat insulating layer 612, an electromagnetic induction heat generating layer 613, and a release layer 615 in this order from the inside to the outside. An elastic layer 614 is provided between the heat generating layer 613 and the release layer 615 so that it can be satisfactorily performed.

  A magnetic flux generating device 60 disposed outside the fixing roller 61 and facing the roller 61 causes the generated magnetic flux to act on the electromagnetic induction heat generating layer 613 to generate an eddy current. The electromagnetic induction heat generating layer 613 is a thin layer, and has a small heat capacity and is thermally insulated and held by the heat insulating layer 612. Therefore, the elastic layer 614 on the fixing roller surface layer side, and the release layer 615 can be heated quickly. The surface temperature of the fixing roller 61 can be quickly reached to the temperature necessary for fixing the toner image, and the necessary heat can be easily supplied even if the recording medium is deprived of heat.

As the roller hardness of the fixing roller 61, for example, a hardness selected from a range of about 30 to 90 degrees in terms of ASKER-C hardness can be adopted.
Here, the support layer (core metal) 611 is made of aluminum having a thickness of 4 mm. As long as the material of the support layer 611 can secure the strength, for example, a heat-resistant resin molded pipe such as iron or PPS (polyphenylene sulfide) can be used, but in any case, the support layer 611 generates heat. In order to prevent this, it is desirable to use a non-magnetic material that is less affected by electromagnetic induction heating.

  The heat insulation layer 612 is for heat-retaining and holding the electromagnetic induction heat generation layer 613, and a heat-resistant and elastic rubber material or resin material sponge body (heat insulation structure) is used. By using a heat-resistant and elastic rubber or resin sponge (heat insulating structure) for the heat insulating layer 612, the heat insulating layer 612 can be held in a heat insulating state, and the electromagnetic induction heat generating layer 613 can be bent and the pressure nip N Can be increased and the roller hardness can be reduced to improve the recording medium discharge performance and the recording medium separation performance.

For example, when a silicon sponge material is used for the heat insulating layer 612, the thickness is about 2 mm to 10 mm, more preferably about 3 mm to 7 mm, and the hardness is about 20 degrees to 60 degrees as measured by an Asker rubber hardness meter, more preferably 30 degrees. What is necessary is just to set to about 50 degree | times.
The heat insulating layer 612 may have a two-layer structure of a rubber material and a sponge body. Here, the heat insulating layer 612 is formed of silicon sponge.

  The electromagnetic induction heat generating layer 613 in this example is an endless nickel electroformed belt layer having a thickness of 10 μm to 100 μm, more preferably 20 μm to 50 μm. The electromagnetic induction heating layer 613 may be formed of other materials, for example, a material having a relatively high magnetic permeability μ, such as a magnetic material (magnetic metal) such as magnetic stainless steel, and an appropriate resistivity ρ. . Furthermore, even a non-magnetic material, a conductive material such as a metal can be used by making the material a thin film.

  Further, as the electromagnetic induction heat generating layer 613, a material in which heat generating particles are dispersed in a resin may be used. By using a resin-based material as the electromagnetic induction heat generating layer 613, the separability of the recording medium can be improved.

  The elastic layer 614 serves to improve the adhesion between the recording medium and the surface of the fixing roller 61, and can be a layer of a rubber material or a resin material having heat resistance and elasticity, and can be used at a fixing temperature. A heat-resistant elastomer such as silicon rubber or fluororubber that can be used can be used. Various fillers may be mixed in the elastic layer 614 for the purpose of thermal conductivity, reinforcement, and the like. Examples of the thermally conductive particles include diamond, silver, copper, aluminum, marble, and glass, but practical examples include silica, alumina, magnesium oxide, boron nitride, and beryllium oxide.

  The thickness of the elastic layer 614 is preferably 10 μm to 800 μm, for example, and more preferably 100 μm to 300 μm. When the thickness of the elastic layer 614 is less than 10 μm, it is difficult to obtain the desired elasticity in the thickness direction, and when the thickness exceeds 800 μm, the heat generated in the heat generating layer 613 is generated on the outer peripheral surface of the fixing roller 61. However, the thermal efficiency tends to deteriorate.

  As a preferable example of the elastic layer 614, an elastic layer made of silicon rubber having a JIS hardness of 1 to 80 degrees, more preferably 5 to 30 degrees can be given. Within this JIS hardness range, it is possible to prevent poor toner fixability while suppressing a decrease in strength of the elastic layer and poor adhesion.

As this silicon rubber, specifically, one-component, two-component or three-component or more silicon rubber, LTV type, RTV type or HTV type silicon rubber, condensation type or addition type silicon rubber, etc. are used. it can.
In this example, the elastic layer 614 is a silicon rubber layer having a JIS hardness of 10 degrees and a thickness of 200 μm.

  The outermost release layer 615 is for improving the release property of the surface of the fixing roller, can withstand use at the fixing temperature, and has toner release properties. For example, silicon rubber, fluorine rubber Fluorine resins such as PFA, PTFE, FEP, and PFEP are preferably used. In this example, the release layer 615 is a layer made of a fluorine-based resin, and the thickness is preferably 5 μm to 100 μm, and more preferably 10 μm to 50 μm.

  Moreover, in order to improve an interlayer adhesive force, you may perform the adhesion process by a primer. In addition, a conductive material, an abrasion resistant material, and a good heat conductive material can be added as a filler to the release layer 615 as necessary.

(2-3) Pressure roller 62 (see FIG. 2)
The pressure roller 62 is provided with a silicon sponge rubber layer having a thickness of 3 mm to 10 mm as a heat insulating layer 622 on the outer periphery of an aluminum cored bar 621 having a thickness of 3 mm. Further, in order to improve the surface releasability like the fixing roller 61. In addition, a roller in which a fluorine resin release layer 623 having a thickness of 10 μm to 50 μm, such as PTFE or PFA, is provided on the outer peripheral surface of the layer 622.

  In addition, as long as the material of the metal core 621 of the pressure roller 62 can secure the strength, it is possible to use a heat resistant resin molded pipe such as PPS (polyphenylene sulfide) in addition to the iron material. In order to prevent the cored bar 621 from generating heat, it is desirable to use a nonmagnetic material that is less affected by electromagnetic induction heating.

  The pressure roller 62 is pressed against the fixing roller 61 with a load of 300 N to 500 N, and the nip width in this case is about 5 mm to 15 mm. In some cases, the nip width may be changed by changing the load.

The thickness of the silicon sponge rubber layer can be appropriately changed in accordance with the use conditions in the range of 3 mm to 10 mm. The heat insulating layer 622 may have a two-layer structure of silicon rubber and silicon sponge.
The material and configuration of the roller and the like are not limited to this example. You may change suitably according to an image forming apparatus, a fixing device, etc.

(2-4) About magnetic flux generator 60 (refer to Drawing 2 and Drawing 3)
The magnetic flux generator 60 is arranged along the longitudinal direction of the fixing roller 61 so as to face the fixing roller 61 outside the fixing roller 61.
The magnetic flux generator 60 includes a coil bobbin 64, an exciting coil 65 wound around the coil bobbin 64, and a magnetic core 67.

  The magnetic core 67 is a long member having a trapezoidal cross section and a length dimension substantially corresponding to the longitudinal dimension of the fixing roller 61. As shown by a chain line in FIG. 2, a protrusion 671 toward the fixing roller 61 may be formed at the center, and the heat generation efficiency may be improved by making the cross section E-shaped.

  The magnetic core 67 has a high magnetic permeability and low loss. In the case of an alloy such as permalloy, an eddy current loss in the core increases at a high frequency, so a laminated structure may be used. The core 67 is used for increasing the efficiency of the magnetic circuit and for magnetic shielding. The magnetic circuit portion of the exciting coil 65 and the core 67 may be an air core (no core) if there is a means capable of sufficient magnetic shielding. Further, when a core 67 in which magnetic powder is dispersed in a resin material is used, the magnetic permeability is relatively low, but the core shape can be freely set.

  The excitation coil 65 has a trapezoidal cross section, and has a structure in which a conducting wire is wound along the longitudinal direction of the fixing roller 61 as shown in FIG. 3, and the magnetic body covers the outer surface of the excitation coil 65. A core 67 is provided.

  As shown in FIG. 4, the exciting coil 65 is connected to an exciting coil driving circuit (magnetic flux generator driving circuit) 651 by a high-frequency inverter, and has a frequency of 10 [kHz] to 100 [kHz], 100 [W] to 2000 [W]. High frequency power is supplied. Therefore, a thin wire bundled from several tens to several hundreds is used as a litz wire, and a wire coated with a heat resistant resin is used in consideration of heat transfer to the winding.

  The magnetic flux induced by the alternating current passes through the magnetic core 67 without leaking to the outside, leaks to the outside of the magnetic core for the first time between the protrusions of the core 67, penetrates the electromagnetic induction heating layer 613 of the fixing roller 61, As a result, an eddy current flows through the electromagnetic induction heat generating layer 613 and the heat generating layer itself generates Joule heat. The fixing roller 61 is heated by the heat generated by the electromagnetic induction heat generating layer 613.

  As shown in FIG. 4, the fixing roller 61 is heated and its temperature control is performed by a fixing roller temperature control section in a control unit Cont that controls the operation of the entire image forming apparatus. The surface temperature of the fixing roller 61 detected by the temperature sensor SE is input to the control unit Cont.

  Here, the temperature sensor SE is a thermistor, and is disposed in contact with the surface of the fixing roller 61. The temperature sensor may be in contact with the temperature detection target portion such as the surface of the fixing roller 61 or may be non-contact.

  The control unit Cont basically controls the excitation coil drive circuit 651 by the high-frequency inverter based on the surface temperature information of the fixing roller 61 input from the temperature sensor SE and controls the fixing roller temperature control to the excitation coil 65. Is automatically controlled so that the surface temperature of the fixing roller 61 becomes a fixing temperature suitable for toner image fixing.

  Then, the pressure roller 62 is driven to rotate, and the fixing roller 61 is also driven to rotate. As a result, the conductive layer 613 as the electromagnetic induction heat generating layer of the fixing roller 61 is electromagnetically heated by the action of the magnetic flux generated by the magnetic flux generator 60. Then, in a state where the surface temperature of the fixing roller 61 is controlled to become the fixing temperature, it is conveyed from the timing roller 7 to the pressure nip portion N between the fixing roller 61 and the pressure roller 62 and in the secondary transfer region. The toner image on the belt 4 is transferred by the secondary transfer roller 5 so that the recording medium P carrying the unfixed toner image is sent.

  The recording medium P that has entered the nip portion N is nipped and conveyed by the pressure nip portion N between the rollers 61 and 62 while the unfixed toner image holding surface side faces the fixing roller 61, and thus the toner image is heated by the fixing roller 61. Thus, it is melt-fixed on the recording medium P.

The recording medium P that has passed through the pressure nip N is separated from the fixing roller 61 and discharged and conveyed. At this time, when the recording medium P is stuck to the surface of the fixing roller 61 after passing through the press nip portion, the separation claw 68 disposed in contact with the surface of the fixing roller 61 forces the recording medium P from the roller 61. Separate to prevent jamming.
The separation claw 68 may be arranged not only in contact with the fixing roller 61 but also in non-contact arrangement.

  As shown in FIG. 2, the fixing roller 61 is composed of at least four layers of a support layer 611, a heat insulating layer 612, an electromagnetic induction heat generating layer 613, and a release layer 615 in order from the inside to the outside. A corresponding elastic layer 614 is also provided.

  The magnetic flux generator 60 is located outside the fixing roller 61 and causes the generated magnetic flux to act on the electromagnetic induction heat generating layer 613 from the outer surface side of the fixing roller 61. The electromagnetic induction heat generating layer 613 that contributes to heat generation and generates eddy current is thin, its heat capacity is small, and the electromagnetic induction heat generating layer 613 is insulated and held by the heat insulating layer (sponge layer) 612. The elastic layer 614 and the release layer 615 are heated quickly so that the surface of the fixing roller quickly reaches the temperature required for fixing.

  However, in this example, as described above, the heat capacity of the electromagnetic induction heat generating layer 613 is small and the surface of the fixing roller quickly reaches the temperature required for fixing, but the heat generating layer 613 has a low heat capacity, so that the recording medium P has a low heat capacity. When the heat is taken away, the temperature drop of the fixing roller 61 is large.

  Further, in the fixing device 6 of this example, the separation claw 68 is disposed near the exit of the fixing nip portion N, and the magnetic flux generator 60 covers the fixing roller 61 in the heating region of the fixing roller 61 by the magnetic flux generator 60. Due to such a configuration, it is extremely difficult to dispose the temperature sensor SE near the exit of the fixing nip portion N or in the heating region. Therefore, the temperature sensor SE is disposed in the vicinity of the entrance of the nip portion N.

  Since the temperature sensor SE is thus arranged on the inlet side of the nip portion N, the fixing device 6 has the following problem only by relying on the basic method described above for controlling the fixing roller surface temperature.

  That is, when the surface temperature of the fixing roller 61 is lowered by passing the recording medium P through the nip portion N between the fixing roller 61 and the pressure roller 62 as described above, the temperature drop is caused by the fixing at which the front end of the recording medium P has reached. The part on the roller 61 is detected only when the fixing roller 61 rotates and arrives at the temperature sensor SE on the inlet side of the nip portion. Further, even if a temperature drop is detected by the temperature sensor SE, driving by the high frequency inverter is performed. Since there is a response delay in the temperature increase control of the fixing roller 61 by the circuit 651, the portion of the fixing roller 61 that has not sufficiently increased in temperature proceeds to the nip portion N as it is.

  Thus, for a recording medium having a length in the conveyance direction of the recording medium that is larger than the circumferential length of the fixing rotator, the toner image is fixed at a low temperature following the medium area from the front end of the recording medium where the toner image is fixed at a predetermined fixing temperature. Therefore, a large level difference in image gloss occurs between the two areas, and the image quality deteriorates.

Further, for a recording medium whose recording medium conveyance direction length is equal to or less than the circumferential length of the fixing roller 61, when a toner image is sequentially placed on a plurality of recording media, the image is transferred between the preceding recording medium and the succeeding recording medium. The luster level difference occurs.
The change in gloss is inconspicuous if it changes gradually, but it becomes difficult to ignore the difference in level.

  Further, even if the temperature sensor SE can be arranged on the exit side of the fixing nip portion N, and the temperature of the fixing roller surface portion corresponding to the area following the front end of the recording medium P on the exit side of the fixing nip portion N can be measured. The predetermined power input to the magnetic flux generator 6 (excitation coil 65) from the drive circuit 651 by the high frequency inverter is delayed with respect to the temperature information input from the temperature sensor SE, and the temperature information input from the temperature sensor SE is instantaneously input. In response, the exciting coil 65 cannot be supplied with electric power for raising the temperature of the fixing roller 62 so as to compensate for the temperature drop of the fixing roller 62.

  For example, when the response of the high frequency inverter is 0.3 seconds and the system speed (recording medium conveyance speed) is 250 mm / second, the input power at the time when the temperature sensor SE detects a temperature drop due to the fixing roller 61 passing through the recording medium is If it is 0 [W], the desired power is supplied after the fixing roller 61 has rotated 75 mm in the roller circumferential direction. Therefore, during the time lag due to the responsiveness of the drive circuit 651 by the high-frequency inverter, the fixing process is performed in a state where the fixing roller 61 is not sufficiently heated, so that the glossiness in the toner image fixed image is lowered and a gloss level difference is generated. . The higher the speed of the image forming apparatus, the greater the effect.

  Therefore, for the fixing device 6, the control unit Cont generates a magnetic flux during the next period even if the surface temperature of the fixing roller 61 is being controlled to a fixing temperature suitable for toner image fixing based on the temperature detected by the temperature sensor SE. The drive circuit 651 is controlled so that constant power is supplied to the device 60 (excitation coil 65), and thereafter, the temperature control based on the temperature detected by the temperature sensor SE is returned.

The period is
(1) A length (length L1) for one rotation of the fixing roller in a roller circumferential direction opposite to the rotation direction of the fixing roller from a portion on the fixing roller 61 where the leading end of the recording medium P reaches,
(2) In the circumferential direction of the roller extending from the portion on the fixing roller 61 where the leading end of the recording medium P reaches to the portion on the fixing roller where the trailing end of the recording medium P reaches, the direction opposite to the rotation direction of the fixing roller Between the two lengths L1 and L2, the shorter peripheral surface area of the fixing roller is the heating region of the fixing roller 61 by the magnetic flux generator 60 (the length L2). This is a period from when the magnetic flux generator 60 enters the area covered by the fixing roller 61 until it comes out, and when both the lengths are the same, the fixing roller having a length L1 corresponding to one round of the fixing roller. This is the period from when the peripheral area enters the heating area until it exits.
In this example, the “heating region” is a region where the magnetic flux generator 60 covers the fixing roller 61 from a1 to a2 shown in FIG.

  Here, the length L1 is shorter than the length L2 when the conveyance direction length of the recording medium P is longer than the circumferential length of the fixing roller, and when the conveyance direction length of the recording medium P is shorter than the circumferential length of the fixing roller. , Longer than the length L2. The length L1 is a length corresponding to a known fixing roller circumferential length, and the length L2 is a length corresponding to a known conveyance direction length of the recording medium P.

  Accordingly, when the conveyance direction length of the recording medium P is the same as or longer than the circumferential length of the fixing roller 61, the control unit Cont enters the heating roller in the range of the fixing roller circumferential surface having a length L1 corresponding to one rotation of the fixing roller 61. The period from when the recording medium P is conveyed is shorter than the peripheral length of the fixing roller 61, and the period from when the fixing roller peripheral surface area of the length L2 enters the heating area until it exits. Controls the drive circuit 651 so that constant power is supplied to the magnetic flux generator 60 (excitation coil 65).

  Due to the constant power supply to the magnetic flux generator 60, the surface area of the fixing roller whose temperature has decreased due to the rush of the recording medium P into the nip N between the fixing roller 61 and the pressure roller 62 is returned to the nip N again. Prior to arrival, the temperature rise is started. Thus, the toner image fixed image obtained on the recording medium P does not generate a gloss level difference, or even if it occurs, the level can be suppressed to a level that can be ignored in practice, and the quality is high. Thus, a fixed toner image can be obtained.

  In this example, the constant power is based on the temperature detected by the temperature sensor SE when the toner images are sequentially fixed on two or more recording media without applying the constant power. The average power of the electric power input from the drive circuit 651 to the magnetic flux generator 60 under the instruction of the controller Cont is adopted so that the fixing roller 61 moves toward the fixing temperature.

  When the control unit Cont causes the magnetic flux generation device 60 to input constant power from the drive circuit 651 during the period, the control unit Cont uses the timing roller 7 as a reference to drive the power supply instruction timing to the drive circuit 651 and drive by the high-frequency inverter. Considering that the constant power input from the circuit 651 to the exciting coil 65 is started with a response delay with respect to the instruction from the control unit Cont, it is determined as follows.

From the position of the timing roller 7, it passes through the secondary transfer area, enters the fixing nip N between the fixing roller 61 and the pressure roller 62, exits there, and then enters the fixing roller heating area entrance a <b> 1 along the peripheral surface of the fixing roller 61. Ls [mm], the distance to
The response delay of the drive circuit 651 is X (seconds),
System speed (medium P transport speed) is Y [mm / sec],
The elapsed time from the start of conveyance of the recording medium by the timing roller 7 is t [seconds],
If the distance that the leading edge of the recording medium advances during the elapsed time is Lp [mm], the remaining distance from the leading edge position of the recording medium to the heating area inlet is (Ls−Lp),
The time required for the recording medium P to travel this distance (Ls−Lp) is (Ls−Lp) / Y. If the time (Ls−Lp) / Y substantially equals the response delay to X, the time on the fixing roller 61 At the timing when the portion of the recording medium leading edge reaches the heating region, the desired constant power is started to be applied to the magnetic flux generator 60.

  Therefore, after the timing roller 7 starts conveying the recording medium, the control unit Cont takes a time required for the leading edge of the recording medium to advance a distance Lp (= Y × t) that substantially satisfies the condition (Ls−Lp) / Y = X. The drive circuit 651 is instructed to start constant power input at the elapse of t.

Such power-on instruction timing may be set according to the system speed Y [mm / sec], the distance Ls [mm] from the timing roller to the heating area entrance, the response delay X [sec] of the drive circuit 651, and the like.
Taking the case of a response delay X = 0.3 seconds and a distance Ls = 200 mm as an example, the medium roller tip travel distance Lp [mm] based on the timing roller position corresponding to the system speed for determining the power-on instruction timing is shown below. .
System speed Media tip travel distance Lp 300 [mm / sec] 110 [mm]
200 [mm / sec] 140 [mm]
150 [mm / sec] 155 [mm]
100 [mm / sec] 170 [mm]

  Whether or not the fixing roller peripheral surface area having the length L1 or the length L2 has left the heating region is determined by [(known fixing roller peripheral length) / system speed], [(known speed) in the controller Cont. It is possible to grasp from the elapsed time obtained by calculation from the time required for passing through the heating area (a1 to a2), etc.

Next, the operation of the control unit Cont will be described with reference to FIG.
First, when a print command is input from the operation panel PN connected to the control unit Cont, the surface temperature of the fixing roller 61 is controlled to be adjusted to the fixing temperature based on the detected temperature from the temperature sensor SE (step S1).

  When the timing roller 7 is not transporting the recording medium (here, the recording paper), the temperature control by the temperature sensor SE is continued, and when the fixing roller 7 is transporting the recording paper, The temperature control by the temperature sensor SE is continued if the recording paper leading edge reaching portion has not yet entered the heating region. However, when entering the heating region, the constant power is supplied to the exciting coil 65 (steps S2 to S5). .

  Then, when the fixing roller peripheral surface area for one rotation of the fixing roller from the portion on the fixing roller 61 where the leading edge of the recording paper has reached the heating region, the temperature control is returned to the temperature control by the temperature sensor SE (steps S6 and S8). When the peripheral surface area of the fixing roller having a length corresponding to one circumference of the roller has not yet come out of the heating area, it is determined by checking whether or not the area where the recording paper trailing edge has reached the fixing roller 61 has left the heating area. If so, the constant power input is continued (steps S7 and S5). When it is determined that the toner image has been discharged, if the toner image fixing process is to be continued on the next recording sheet, the process returns to step S1 to return to the normal temperature control, and if there is no next recording sheet, the printing ends. (Step S10).

  After the fixing roller circumferential surface area for one rotation of the fixing roller has exited the heating region from the portion on the fixing roller 61 where the leading edge of the recording paper has reached, the temperature control is resumed by the temperature sensor SE (steps S6 and S8). When the trailing edge of the paper exits the fixing nip N, if the toner image fixing process is to be performed on the next recording paper, the process returns to step S1 to return to the normal temperature control, and if there is no next recording paper. The printing ends (steps S9 and S10).

  However, when the trailing edge of the recording paper has not yet come out of the fixing nip portion N, it is checked whether the timing roller 7 is transporting the next recording paper. If not, the process returns to step S8.

  When the length of the recording sheet in the conveyance direction is shorter than one rotation of the fixing roller 61, the timing roller 7 conveys the next sheet during a period in which the portion corresponding to the rear end of the current recording sheet on the fixing roller 61 is in the heating region. The position of the timing roller 7 and the interval between the sheets are set so that the position on the fixing roller 61 where the leading edge of the recording paper reaches after the timing roller 7 transports the preceding recording paper enters the heating region. It is necessary to set the position of the timing roller 7 and the interval between the sheets so that the sheet is not conveyed by the timing roller 7.

Also, if the type of recording medium is different, the fixing temperature suitable for fixing the toner image changes, and the number of recording media that pass through the fixing nip N per unit time may vary depending on the type of recording medium. The “electric power that compensates for the amount of heat taken from the fixing roller 61 and moves the fixing roller temperature to the fixing temperature corresponding to the medium type” also differs. Accordingly, it is desirable to change and set the “constant power” according to the type of medium used. For example, if there are three types of recording media employed, P1, P2, and P3, and the amount of heat taken from the fixing roller in the order of P1, P2, and P3 is large, the “constant power” is large as illustrated in the following table. The case where it changes is mentioned.
Recording medium type Constant power
P1 980 [W]
P2 860 [W]
P3 800 [W]

  In addition, the amount of heat taken from the fixing roller 61 during the toner image fixing process varies depending on the size of the recording medium, whether it is a color image or a monochrome image, etc. In addition to adjusting the “constant power” according to the type of recording medium. The “constant power” is desirably adjusted according to at least one of a recording medium size, a color image, and a monochrome image.

The recording medium conveyance position can be determined by using an optical sensor, a mechanical sensor, or the like in addition to the case where the position of the timing roller 7 is used as a reference as described above.
Further, the image forming apparatus A described above is a tandem type color image forming apparatus, but the present invention can be applied to other types of color image forming apparatuses and monochrome image forming apparatuses.
Furthermore, the present invention can be applied to various image forming apparatuses such as a copying machine, a printer, a facsimile machine, and a multi-function machine combining two or more of these.

  The present invention provides a fixing device that heats and melts an unfixed toner image formed on a recording medium and fixes the image on the recording medium in an image forming apparatus such as a copying machine or a printer, and an image forming apparatus including the fixing device. Can be used to do.

1 is a diagram illustrating an outline of a configuration of an example of an image forming apparatus including an example of a fixing device according to the present invention. FIG. 2 is a cross-sectional view of a main part of a fixing device in the image forming apparatus of FIG. 1. FIG. 3 is a diagram showing a fixing device portion shown in FIG. 2 as viewed from the left side in FIG. 2. FIG. 2 is a block diagram illustrating an outline of a control circuit of the image forming apparatus illustrated in FIG. 1. 5 is a flowchart illustrating an example of control of the fixing device by a control unit.

Explanation of symbols

A Color printer Y Yellow image forming unit M Magenta image forming unit C Cyan image forming unit K Black image forming unit YC Yellow process cartridge MC Magenta process cartridge CC Cyan process cartridge KC Black process cartridge 11 Photoconductor 12 Charging device 13 Image exposure device 14 Developing device 141 Developing roller 15 Cleaning device 2 Primary transfer roller 31 Driving roller 32 Opposed roller 4 Intermediate transfer belt 5 Secondary transfer roller 40 Cleaner 7 Timing roller P Recording medium

6 Fixing Device 61 Fixing Roller 611 Support Layer 612 Heat Insulating Layer 613 Electromagnetic Induction Heating Layer 614 Elastic Layer 615 Release Layer 62 Pressing Roller 621 Core Bar 622 Core Bar Outer Layer 623 Release Layer N Pressing Nip Portion (Fixing Nip Portion) )
68 Separation claw SE Temperature sensor 60 Magnetic flux generator 64 Coil bobbin 65 Excitation coil 651 Excitation coil drive circuit 67 Core 671 Core protrusion Cont Control unit PN Operation panel

Claims (5)

A rotatable fixing rotator having an electromagnetic induction heat generating layer, a rotatable pressure rotating body pressed against the fixing rotator, and a magnetic flux generator for generating heat from the electromagnetic induction heat generating layer of the fixing rotator, The magnetic flux generating device generates heat in the electromagnetic induction heat generating layer of the fixing rotator, and the recording medium holding the toner image is passed through the nip portion between the fixing rotator and the pressure rotator, thereby causing the toner image to pass through the recording medium. A fixing device for fixing on a recording medium;
A temperature sensor for detecting a surface temperature of the fixing rotator on the inlet side of the nip portion;
A controller that controls the drive circuit of the magnetic flux generator so that the surface temperature of the fixing rotator is set to a predetermined toner image fixing temperature based on the temperature detected by the temperature sensor;
The control unit is configured to fix the toner image on the recording medium even when the driving circuit of the magnetic flux generator is being controlled so that the surface temperature of the fixing rotator is directed to the fixing temperature. The fixing rotor peripheral surface area having a predetermined length in the circumferential direction of the fixing rotator opposite to the rotation direction of the fixing rotator from the portion on the fixing rotator reached by the magnetic flux generator is a fixing rotator heating area by the magnetic flux generator. A fixing device, wherein the drive circuit is controlled so that a predetermined constant power is supplied to the magnetic flux generator during a period from entering to exiting. The period of supplying a predetermined constant power to the magnetic flux generator is as follows:
A length of one rotation of the fixing rotator in a circumferential direction of the fixing rotator opposite to the direction of rotation of the fixing rotator from a portion on the fixing rotator at which the leading end of the recording medium reaches;
The length in the circumferential direction of the fixing rotator extending from the portion on the fixing rotator at which the leading end of the recording medium reaches to the portion on the fixing rotator at which the trailing end of the recording medium reaches in the direction opposite to the rotation direction of the fixing rotator. When there is a difference between them, it is a period from the time when the peripheral surface area of the fixing rotator having the shorter one of the two lengths enters the fixing rotator heating area by the magnetic flux generator until it comes out, 2. The fixing device according to claim 1, wherein when the lengths are the same, the fixing rotor peripheral surface area having a length corresponding to one rotation of the fixing rotor is a period from entering the fixing rotor heating area to exiting. .   The predetermined constant power supplied to the magnetic flux generator is determined by the temperature sensor when the toner images are sequentially fixed on two or more recording media without applying the constant power. The average power of the electric power input from the drive circuit to the magnetic flux generator under the instruction of the control unit so that the fixing rotating body moves toward the fixing temperature based on the detected temperature. The fixing device described.   The fixing device according to claim 1, wherein the control unit switches a constant power input to the magnetic flux generator according to a recording medium type.   An image forming apparatus that forms an electrostatic latent image corresponding to an image to be formed on an image carrier, develops the electrostatic latent image into a toner image, and fixes the toner image to a recording medium by a fixing device. An image forming apparatus comprising the fixing device according to claim 1 as the fixing device.