JP4725361B2 - 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 an electrophotographic copying machine or a printer, and in particular, fixes the recording medium to the recording medium. The present invention relates to a fixing device using an induction heating type heat source as a heat source. The present invention also relates to an image forming apparatus provided with the fixing device.

  A fixing device employed in an image forming apparatus such as an electrophotographic system generally includes a rotatable fixing roller, a rotatable pressure roller that is pressed against the fixing roller, and a heat source that heats the fixing roller. The fixing roller is heated by the heat source, and the recording medium holding the toner image is passed through the nip portion between the fixing roller and the pressure roller, so that the toner image is melt-fixed to the recording medium under pressure. Let

  As such a heat source, a heating element (heater or the like) provided on the inside or the outer peripheral surface of the fixing roller has been adopted. However, due to today's demand for energy saving, an electromagnetic induction heating type heat source that can obtain high heat conversion efficiency. 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 heat roller type fixing device using a conventional halogen lamp heater has been obtained, the rise to the fixing temperature for fixing a toner image is rapid, and the fixing device is made compact. As a fixing device capable of the above, 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 roller by a core material such as a ferrite core has been proposed.

  For example, a rotatable fixing roller having an electromagnetic induction heat generating layer, a rotatable pressure roller pressed against the fixing roller, and a magnetic flux for causing the electromagnetic induction heat generating layer of the fixing roller to generate electromagnetic induction heat. There is a fixing device that heats the fixing roller by generating an electromagnetic induction heat generating layer of the fixing roller by the magnetic flux generated by the magnetic flux generating device.

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. ing.
According to the electromagnetic induction heating type fixing device, the electromagnetic induction heat generating layer in the fixing roller 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. However, there is no problem in heating the fixing roller to the fixing temperature.

  However, when the heat capacity of the electromagnetic induction heat generating layer is reduced in this way, for example, when fixing a toner image on a small size recording medium, the portion of the fixing roller outside the passing area of the small size recording medium is When the toner image is fixed on a large-sized recording medium because the temperature is excessively high because the recording medium is not in contact with the recording medium, the excessively heated fixing roller portion comes into contact with the toner image on the large-sized recording medium. In other words, a so-called high temperature offset (a phenomenon in which melted toner adheres to the fixing roller) occurs, resulting in image defects, and thermal deterioration of fixing device members such as the fixing roller and exposure of members around the fixing device to high heat. Receive.

  In this regard, by placing a cancel coil (demagnetization coil) on the exciting coil portion corresponding to the electromagnetic induction heating layer portion outside the passage area of the small size recording medium of the fixing roller, the electromagnetic induction heating layer portion It has also been proposed to suppress fever.

For example, in Japanese Patent Application Laid-Open Nos. 2001-60490 and 2001-135470, in an electromagnetic induction heating type fixing device in which a magnetic flux generator is provided inside a fixing roller having an electromagnetic induction heat generating layer, the fixing roller is small. It is described that a cancel coil is allowed to face an exciting coil portion corresponding to an electromagnetic induction heat generating layer portion outside the size recording medium passage region to suppress heat generation of the electromagnetic induction heat generating layer portion.
That is, when fixing a toner image on a large size recording medium, the cancel coil is opened so that the cancel coil does not act. However, when fixing a toner image on a small size recording medium, the cancel coil is closed, A counter electromotive force in a direction to cancel the magnetic field is induced in the cancel coil by the magnetic field generated by the exciting coil, thereby suppressing heat generation in the electromagnetic induction heating layer portion.

Japanese Patent No. 2616433 JP 2001-60490 A JP 2001-135470 A

  However, the cancel coil (demagnetizing coil) described in Japanese Patent Application Laid-Open Nos. 2001-60490 and 2001-135470 continues to be closed in the toner image fixing process on a small-size recording medium. Therefore, the temperature of the portion outside the small size recording medium passage area of the fixing roller is maintained lower than the temperature for fixing the toner image required for the small size recording medium passage area, and the small size is affected by the influence. There is a possibility that the temperature of the recording medium passing area also decreases and fixing failure occurs.

  In addition, for example, when there are three types of recording media to be subjected to toner image fixing processing, for example, large, medium and small, in order to suppress an excessive temperature rise outside the recording medium passage area of the fixing roller, the passage area of the smallest size recording medium Assuming that the cancel coil (demagnetizing coil) faces the exciting coil portion corresponding to the electromagnetic induction heating layer portion on the outer side of the toner, the recording medium subject to toner image fixing processing has changed to a medium size medium larger than the minimum size recording medium. Sometimes, the cancellation coil must be opened and not act as in the case of a large size recording medium. When fixing a toner image on a large-sized recording medium, problems such as high temperature offset occur due to the excessively heated fixing roller portion. There is a Les.

  As described above, in the induction heating type fixing device employing the cancel coil (demagnetization coil) that has been proposed so far, the opening and closing of the cancel coil is simply performed depending on whether the recording medium is a small size recording medium or a larger recording medium. Since the opening / closing control is performed, various problems such as an inability to perform satisfactory toner image fixing processing corresponding to recording media of various sizes may occur.

The present invention includes a rotatable fixing roller having an electromagnetic induction heat generating layer, a rotatable pressure roller to be pressed against the fixing roller, for generating a magnetic flux to heat the electromagnetic induction heating layer of the fixing roller A magnetic flux generating device including an exciting coil. The magnetic flux generating device generates heat from the electromagnetic induction heating layer of the fixing roller, and passes through a recording medium holding a toner image at a nip portion between the fixing roller and the pressure roller. A fixing device capable of fixing the toner image onto the recording medium, and even when there are a plurality of recording media to be subjected to toner image fixing processing, the recording on the fixing roller is performed on the recording medium of each size. It is a first object to provide a fixing device that can satisfactorily perform a toner image fixing process while suppressing an excessive temperature rise in an outer portion of a medium passing area.

  The present invention also forms an electrostatic latent image on the electrostatic latent image carrier, develops the electrostatic latent image to form a toner image, transfers the toner image to a recording medium, and fixes it with a fixing device. A second object is to provide an image forming apparatus that can form a good image.

In order to solve the first problem, the present invention provides:
Flux comprising a rotatable fixing roller having an electromagnetic induction heat generating layer, a rotatable pressure roller to be pressed against the fixing roller, an exciting coil for generating a magnetic flux to heat the electromagnetic induction heating layer of the fixing roller The magnetic induction heat generating layer of the fixing roller is heated by the magnetic flux generator, and the recording medium holding the toner image is passed through the nip portion between the fixing roller and the pressure roller. An image can be fixed on the recording medium, and three or more types of recording media having different sizes in a direction orthogonal to the passing direction of the recording medium can be passed through the nip portion to fix the toner image on the recording medium. A fixing device that can
A temperature control temperature sensor for detecting the temperature of the passing area of the minimum size recording medium in the fixing roller;
Excitation for controlling the excitation coil based on the temperature of the passage area detected by the temperature adjustment temperature sensor so that the temperature of the passage area is set to a predetermined temperature adjustment temperature required for the toner image fixing process. A coil controller;
A degaussing coil disposed outside the passing area width of the recording medium of the smallest size among the recording media to be subjected to toner image fixing processing and arranged adjacent to the end of the exciting coil in accordance with the passing area width of the recording medium having a predetermined size. When,
A switching circuit for opening and closing the demagnetizing coil;
A degaussing coil controller that controls opening and closing of the degaussing coil by the switching circuit;
An end temperature sensor for detecting the temperature of the end of the fixing roller outside the passing area width of the minimum size recording medium,
The demagnetizing coil control unit determines the fixing roller end temperature for each size of the recording medium to be subjected to toner image fixing processing based on the fixing roller end temperature detected by the end temperature sensor . And a fixing device for controlling opening and closing of the degaussing coil by controlling the switching circuit so as to go to a fixing roller end temperature control set temperature for suppressing excessive temperature rise .

Here, the “demagnetizing coil” is a coil for inducing a counter electromotive force in a direction to cancel the magnetic field by the magnetic field generated by the exciting coil.
“Closing the degaussing coil” is to construct a closed circuit including the degaussing coil so that a current (inductive current) flows through the degaussing coil due to the back electromotive force induced in the degaussing coil. “Opening a coil” means breaking (opening) the closed circuit. The “recording medium size” is a recording medium width size in a direction orthogonal to a direction in which the recording medium is passed through the fixing device.
“Preset temperature for fixing roller end temperature control according to the size of the recording medium” means that when a toner image fixing process is performed on a recording medium of that size, the temperature outside the passage area of the recording medium of that size The temperature is such that the excessive temperature rise of the fixing roller portion can be suppressed and the toner image fixing process to the recording medium of that size is not hindered.

According to the fixing device of the present invention, the degaussing coil control unit performs the toner image fixing process based on the temperature information detected by the end temperature sensor , based on the temperature information detected by the end temperature sensor. Since the switching circuit is controlled so that the fixing roller end temperature control temperature is set in accordance with the size of the fixing roller, and the opening and closing of the degaussing coil is controlled, the toner image is fixed onto the recording medium of that size. The processing can be performed satisfactorily while suppressing excessive temperature rise of the fixing roller portion outside the passing area of the recording medium of that size.

In the fixing device according to the present invention, three or more types of recording media having different sizes in the direction orthogonal to the passing direction of the recording medium in the fixing device are passed through the nip portion to fix the toner image on the recording medium. Although as it can, the fixing roller end portion temperature control set temperature of the can than respectively predetermined for each size of the recording medium for the toner image fixing process, their respective size of the recording medium In addition, the toner image fixing process can be satisfactorily performed while suppressing an excessive temperature rise in the outer portion of the recording medium passage area.

  A plurality of fixing roller end temperature control set temperatures can be determined according to the size of the recording medium targeted for toner image fixing processing. If there is no problem, it is also possible to set a common set temperature for both types of recording media of a plurality of recording media sizes, for example. Further, it may be determined based on one or more of the print mode, the image forming speed, etc. in the image forming apparatus.

As the end portion temperature sensor, Ru can be given a temperature sensor such as a thermistor as a representative example. For reference , when a toner image fixing process is continuously performed on a plurality of recording media of the same size, and the fixing roller end temperature changes depending on the size and the number of the recording media, the recording medium It is also possible to calculate the fixing roller end temperature from the size and the number of toner image fixing processes on the recording medium of that size, and use this as the detected temperature. In this case, the temperature calculation may be performed, for example, by giving a calculation function to the degaussing coil control unit. In that case, a portion having the calculation function in the degaussing coil control unit is a temperature detection unit.

The end temperature sensor may be provided at the end of the fixing roller, or may be provided at the end of the pressure roller that is in pressure contact with the end of the fixing roller.
Also, ensure the multi size of the recording medium, favorably to accommodate the end portion temperature sensor, in the outer region than the pass area of the maximum size recording medium of the toner image fixing processing target recording medium and the nip region You may provide so that the temperature of the part of the said fixing roller may be detected.

For example, the demagnetizing coil control unit controls the switching circuit so that the demagnetizing coil is closed when the temperature detected by the end temperature sensor exceeds the fixing roller end temperature control set temperature. The switching circuit is controlled so that the demagnetizing coil is opened when the temperature detected by the end temperature sensor is equal to or lower than the fixing roller end temperature control set temperature.

  The demagnetizing coil control unit controls the switching circuit so that the degaussing coil is closed when the temperature detected by the end temperature sensor starts to rise to a predetermined first temperature or higher. The switching circuit may be controlled so that the degaussing coil is opened when the temperature detected by the end temperature sensor starts to fall below a predetermined second temperature.

  The case where 1st temperature is set lower than 2nd temperature can be illustrated as said 1st temperature and 2nd temperature in the case of employ | adopting this degaussing coil control part. Furthermore, a case where the first temperature is lower than the fixing roller end temperature control set temperature and the second temperature is higher than the fixing roller end temperature control set temperature can be exemplified.

  The demagnetizing coil control unit may determine that an abnormality has occurred when a rising width of the temperature detected by the temperature sensor exceeds a predetermined rising width at a predetermined time. Further, based on the determination, a signal such as a signal for stopping the image forming operation of the fixing device or the image forming apparatus in which the fixing device is mounted may be issued.

The fixing roller end temperature control set temperature may be a temperature calculated based on the size of the recording medium targeted for toner image fixing processing and the number of recording media on which toner image fixing processing is performed using the recording medium of that size.
Such a set temperature calculation may also be performed, for example, by providing the degaussing coil control unit with the calculation function.

In any case, the set temperature for fixing roller end temperature control may be different from the temperature adjustment temperature of the fixing roller for fixing the toner image.
A soaking member may be disposed in contact with the surface of the fixing roller or the pressure roller.

  In order to solve the second problem, the present invention forms an electrostatic latent image on an electrostatic latent image carrier, develops the electrostatic latent image to form a toner image, and records the toner image. There is also provided an image forming apparatus for transferring to a medium and fixing with a fixing device, wherein the fixing device is a fixing device according to the present invention.

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 image accordingly.
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 usually directly transferred to a recording medium 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.

According to the present invention described above, the magnetic flux generating heat a rotatable fixing roller having an electromagnetic induction heat generating layer, a rotatable pressure roller to be pressed against the fixing roller, an electromagnetic induction heat generating layer of the fixing roller A magnetic flux generation device including an exciting coil for generating heat, and the magnetic flux generation device generates heat at an electromagnetic induction heat generation layer of the fixing roller and holds a toner image at a nip portion between the fixing roller and the pressure roller. A fixing device capable of fixing the toner image to the recording medium by passing the recording medium to be recorded, and when there are a plurality of recording media to be subjected to toner image fixing processing, It is possible to provide a fixing device that can satisfactorily perform a toner image fixing process while suppressing an excessive temperature rise in the outer side of the recording medium passage area in the fixing roller.

  According to the present invention, an electrostatic latent image is formed on the electrostatic latent image carrier, the electrostatic latent image is developed to form a toner image, the toner image is transferred to a recording medium, and fixed by a fixing device. It is possible to provide an image forming apparatus that can form a good image.

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 PR that can form a color image.
The color printer PR has a drive roller 31 and an endless intermediate transfer belt 4 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 8 for cleaning secondary transfer residual toner and the like on the transfer belt 4 faces the transfer belt portion on the opposing 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 pair 9 is disposed below the secondary transfer roller 5, and a recording medium housing cassette that houses a recording medium (not shown) is disposed below the pair of timing rollers 9.
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 a recording medium storage cassette (not shown) can be pulled out one by one by a medium supply roller (not shown) and supplied to the timing roller pair 9.
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 can perform image exposure on the photoconductor 11 using a laser beam in accordance with image information provided from a personal computer (not shown).

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.

According to the printer PR, an image can be formed using one or more of the 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 a recording medium storage cassette (not shown) by a medium supply roller, supplied to the timing roller pair 9, and is on standby.

  The recording medium P waiting at the timing roller pair 9 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, and is not shown. The multiple toner images are secondarily transferred onto a recording medium by a secondary transfer roller 5 to which a secondary transfer bias is applied from a power supply device.

  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 is continuously discharged to a discharge tray by a pair of discharge rollers (not shown).

[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, a temperature equalizing roller 63 pressed against the pressure roller 62, and a magnetic flux generating device 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.

  The pressure roller 62 is rotationally driven in a counterclockwise direction indicated by an arrow in FIG. The fixing roller 61 is rotated by the rotation of the pressure roller 62 by a pressure frictional force with the pressure roller 61 at the pressure nip N or by a pressure friction force with the recording medium P being nipped and conveyed at the nip N. To do.

  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 passing area of the fixing roller 61 becomes a temperature suitable for toner image fixing. 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 T that has come out is fed into the pressure nip N between the fixing roller 61 and the pressure roller 62. At this time, the unfixed toner image carrying surface on 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 T 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 separated from the fixing roller 61 and discharged and conveyed.

  The soaking roller 63 is brought into contact with the entire area in the rotational axis direction of the pressure roller 62 [longitudinal direction (width direction) of the roller 2] by a pressing device including a pressing spring (not shown), and is driven to rotate by the pressure roller 62. To do. The soaking roller 63 incorporates a heater lamp 631 as a heating source. The outer cylindrical portion of the soaking roller 63 is preferably made of a metal material having good thermal conductivity, and in this example, is made of an aluminum material. In addition to the heater lamp, other heat sources such as a resistance heating element may be used as the heat source.

(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 supplied even if the recording medium is deprived of heat.

As the roller hardness, 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 3 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 12 mm, more preferably about 3 mm to 10 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.

Further, if a heat insulating layer having a two-layer structure of a solid rubber layer as a lower layer and a sponge rubber as an upper layer is used as the heat insulating layer 612, the durability of the fixing roller 61 can be improved.
The fixing roller having the heat insulating layer 612 having a two-layer structure is used in order to secure the width of the nip portion N, particularly when the fixing device is used under relatively severe conditions such as being used under high load or high speed rotation. When the thickness of the heat insulating layer 612 is set to be thick or when a soft sponge layer is used, it is effective for suppressing rubber breakage in the heat insulating layer 612.

  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. The thickness of the release layer 615 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)
In the pressure roller 62, a layer 622 is provided on the outer periphery of the iron cored bar 621. Further, in order to improve the surface releasability like the fixing roller 61, the outer surface of the layer 622 has a thickness of, for example, PTFE or PFA. This is a roller provided with a release layer 623 made of fluororesin having a thickness of 10 μm to 50 μm.
In this example, the layer 622 is made of silicon sponge rubber having a thickness of 3 mm to 10 mm.

  In addition, as long as the material of the metal core 621 of the pressure roller 62 can ensure 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 addition, a solid rubber layer can be used instead of the silicon foam rubber layer (silicon sponge rubber layer) 622, but the layer 622 has a low heat so as not to let the heat transmitted from the fixing roller 61 through the nip portion N escape. It is desirable to form with the material of conductivity.

  Further, when a layer having a two-layer structure of a solid rubber layer as a lower layer and a sponge rubber as an upper layer is used as the layer 622, durability can be improved while keeping the heat insulation of the pressure roller 62 high. The pressure roller 62 employing the layer 622 having such a two-layer structure is used to secure the width of the nip portion N particularly when the fixing device is used under relatively severe conditions such as high load and high speed rotation. When the thickness of the layer 622 is set thick or when a soft sponge layer is used, it is effective for suppressing rubber breakage in the layer 622.

(2-4) Magnetic flux generator 60 (see FIGS. 2 to 5)
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, a main core 67, and a hem core 68. The magnetic flux generator 60 is also combined with demagnetizing coils 661 and 662 described later.

  In this example, as shown in FIGS. 3 and 4, the exciting coil 65 has a shape that extends long in a direction crossing the recording medium conveyance direction in the fixing device 6 (here, an orthogonal direction), and as shown in FIG. 2. In this structure, a conducting wire is wound around the bobbin 64 so that the cross-sectional shape is an arc shape. A distance Lc (see FIG. 4) between the inner side portions of the bent portions in the direction crossing the recording medium conveyance direction of the exciting coil 65 is substantially equal to the width (length in the longitudinal direction) of the fixing roller 61 in this example. The width of the pressure roller 62 is slightly shorter than the width of the fixing roller 61 as shown in FIG.

  As shown in FIG. 5, the exciting coil 65 is connected to an exciting coil drive circuit C1 including a high frequency inverter, and is supplied with high frequency power of 10 [kHz] to 100 [kHz], 100 [W] to 2000 [W]. It has become so. Accordingly, it is formed using a bundle of dozens to several hundreds of thin wires to form a litz wire, and is covered with a heat resistant resin in consideration of the case where heat is transferred to the winding.

  As shown in FIGS. 2 and 3, a plurality of main cores 67 are arranged so as to cover the outer surface of the exciting coil 65 opposite to the fixing roller 61. Furthermore, a plurality of main cores 67 are sequentially arranged in parallel to each other in the direction in which the exciting coil 65 extends long (the same direction as the longitudinal direction (width direction) of the fixing roller 61).

  Each of the main cores 67 is a mountain-shaped core as a whole in which “C” -shaped linear portions are connected by arc portions extending over the “C” -shaped tops. Both ends of each main core 67 are magnetically connected to a hem core 68 made of the same material as the main core.

  The main core 67 has high magnetic permeability and low loss. The main core 67 is used for increasing the efficiency of the magnetic circuit and for magnetic shielding. A ferrite core is usually used as the core material. However, in the case of an alloy such as permalloy, an eddy current loss in the core increases at a high frequency, and a laminated structure may be used. Further, when a resin material in which magnetic powder is dispersed is used, the magnetic permeability is relatively low, but the shape can be freely set.

Since the main core 67 is formed in a mountain shape as described above, a temperature control temperature sensor S1 (see FIGS. 2 and 3), which will be described later, a wiring cable not shown in FIGS. Can be placed inside the core. Moreover, by setting it as such a shape, the magnetic flux concentration to the edge part temperature sensor S2 mentioned later can also be reduced.
The shape of the main core 67 may be another shape such as an arc shape or a semi-elliptical shape when viewed from the side, in other words, the cross-sectional shape is an arc shape or a semi-elliptical shape.

  The magnetic flux induced by the AC power supply from the drive circuit C1 to the exciting coil 65 passes through the main core 67 without leaking to the outside and is guided from the core 67 to the fixing roller 61 as shown by a broken line in FIG. Then, the electromagnetic induction heat generating layer 613 of the fixing roller 61 is penetrated, and an eddy current is generated in the electromagnetic induction heat generating layer 613 to cause the electromagnetic induction heat generating layer 613 itself to generate heat. The fixing roller 61 is heated by the heat generated by the electromagnetic induction heat generating layer 613.

  FIG. 5 is a block diagram schematically showing a circuit including a controller Cont for controlling the overall operation of the printer PR. The surface of the recording medium passage area of the fixing roller 61 is required for fixing the toner image. The temperature adjustment control for heating to the temperature adjustment (fixing temperature) and controlling to the temperature adjustment temperature is performed by the temperature adjustment control unit CR1 incorporated in the control unit Cont. For this temperature control, a temperature sensor S1 for detecting the temperature of the surface of the substantially central portion of the fixing roller 61 is provided. The temperature sensor S <b> 1 faces the fixing roller 61 from a window 641 formed in the bobbin 64.

In this example, the temperature sensor S1 is a non-contact thermistor, and is disposed inside the main core 67 so as to be close to the surface of the fixing roller 61, and supplies detected temperature information to the temperature control unit CR1.
A contact thermistor may be used as the temperature sensor S1.
The temperature control unit CR1 may be provided outside the control unit Cont, and may be controlled based on an instruction from the control unit Cont.

The fixing roller surface temperature information detected by the temperature sensor S1 is input to the temperature control unit CR1. The temperature control unit CR1 controls the excitation coil drive circuit C1 including the high-frequency inverter based on the temperature information input from the sensor S1 to increase or decrease the power supply from the circuit C1 to the excitation coil 65, thereby fixing the fixing roller. The heat generation of the electromagnetic induction heat generating layer 613 of 61 is controlled so that the surface temperature of the recording medium passing region of the fixing roller 61 is automatically controlled to a predetermined fixing temperature.
The temperature control temperature sensor S1 may be another sensor such as a thermostat for ensuring safety.

  Thus, the electromagnetic induction heat generating layer 613 of the fixing roller 61 is electromagnetically heated by the action of the magnetic flux generated by the excitation coil 65 of the magnetic flux generator 60, and the surface temperature of the recording medium passing area of the fixing roller 61 is suitable for fixing the toner image. A pressure nip portion between the fixing roller 61 and the pressure roller 62 is automatically controlled so as to reach a temperature (fixing temperature), and the pressure roller 62 is rotationally driven. By passing the recording medium P carrying the toner image T through N, the unfixed toner image T and the recording medium P are heated by the fixing roller 61, and the unfixed toner image T 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.

(2-5) Degaussing coils 661 and 662 (see FIGS. 2 to 5 etc.)
As described above, left and right degaussing coils 661 and 662 are incorporated in the magnetic flux generator 60. The left and right degaussing coils 661 and 662 are the same in this example.
The degaussing coil 661 is arranged on one end of the exciting coil 65 inside the main core 67, and the degaussing coil 662 is arranged on the other end of the exciting coil 65 inside the main core 67. Yes.

The degaussing coils 661 and 662 induce a counter electromotive force in the direction to cancel the magnetic field generated by the magnetic field generated by the excitation coil 65, and thereby the portions of the electromagnetic induction heating layer 613 of the fixing roller 61 corresponding to the demagnetization coils 661 and 662. This is to suppress the heat generation.
As shown in FIG. 5, the degaussing coils 661 and 662 can be controlled to open and close by relay switches SW1 and SW2 in a switching circuit C2 provided separately from the exciting coil drive circuit C1.

When the switch SW1 is closed in the switching circuit C2 shown in FIG. 5, a closed circuit including the degaussing coil 661 is formed (the demagnetizing coil 661 is closed), and when the switch SW1 is opened, the closed circuit is shut off (degaussing coil). 661 open state is formed).
When the switch SW2 is closed, a closed circuit including the demagnetizing coil 662 is formed (the demagnetizing coil 662 is closed), and when the switch SW2 is opened, the closed circuit is shut off (the demagnetizing coil 662 is opened). ).
When the demagnetizing coils 661 and 662 are closed by closing the switches SW1 and SW2, an induced current (in the electromagnetic induction heating layer 613 of the fixing roller 61 is induced at the end of the fixing roller 61 due to a change in magnetic flux generated by the exciting coil 65. In addition to the generation of eddy current, back electromotive force (current associated therewith) in the degaussing coils 661 and 662 also occurs. Therefore, eddy currents in the electromagnetic induction heat generating layer 613 corresponding to the demagnetizing coils 661 and 662 are reduced, heat generation in the heat generating layer is suppressed, and temperature rise at the end of the fixing roller is suppressed.
When the degaussing coils 661 and 662 are opened, the action of the exciting coil 65 is restored.

  In order to control the temperature of the fixing roller end by the demagnetizing coil, as shown in FIGS. 2, 3, and 4, an end temperature sensor S2 is provided in a non-contact manner at the end of the fixing roller 61. The temperature sensor S2 is a non-contact thermistor in this example.

  Further, as shown in FIG. 5, a degaussing coil control unit CR2 for opening and closing the degaussing coils 661 and 662 by opening and closing the relay switches SW1 and SW2 of the switching circuit C2 is incorporated in the control unit Cont. . In this example, the degaussing coil control unit CR2 is determined in accordance with the temperature information input from the end temperature sensor S2 and the recording medium size, and is used for fixing roller end temperature control for each stored recording medium size. Based on the temperature, the relay switches SW1 and SW2 for each degaussing coil in the switching circuit C2 are opened and closed to control the opening and closing of each degaussing coil (in other words, each switch SW1 and SW2 is controlled to open and close, respectively) The operation time of the degaussing coil is controlled), thereby controlling the fixing roller end temperature toward the fixing roller end temperature control setting temperature.

  Here, the setting temperature for fixing roller end temperature control determined according to the size of the recording medium can suppress an excessive temperature increase at the end of the fixing roller outside the passing region on the fixing roller 61 of the recording medium of that size. The toner image can be fixed on the recording medium of that size without any trouble.

The set temperature may be a temperature calculated based on the size of the recording medium and the number of continuous recording media of the size to the fixing device 6 (the number of recording media on which toner image fixing processing is continuously performed).
When the number of recording media continuously passed through the fixing device 6 increases, the state in which there is no recording medium contact with the fixing roller portion outside the passage region of the recording medium continues for a long time, and the temperature of the end of the fixing roller increases. This is because it becomes larger.
Calculation of the set temperature based on the size of the recording medium and the number of continuously passing recording media of the size to the fixing device 6 can be performed, for example, by giving the function to the degaussing coil controller CR2.

The two switches SW1 and SW2 may be replaced with one switch common to both the degaussing coils 661 and 662.
Further, the degaussing coil control unit CR2 may be provided outside the control unit Cont so as to perform a control operation based on an instruction from the control unit Cont.

An operation panel PN is connected to the control unit Cont, and the operation panel PN is used to select a numeric keypad for setting the number of image formations (therefore, the number of recording media passed through the fixing device 6) and the like, and a recording medium size to be employed. A paper size selection key and the like are mounted.
The recording medium size to be taken into account when the degaussing coil control unit CR2 controls the opening / closing of the degaussing coil (demagnetization coil operating time) is input by the paper size selection key. Further, when the degaussing coil controller CR2 takes into account the number of recording media passed to the fixing device 6 in controlling the opening / closing of the degaussing coil (demagnetization coil operating time), the number of recording media is the number input by the numeric keypad. Use it.

  Further, the degaussing coil controller CR2 further obtains a temperature rise width for a predetermined time based on the detected temperature information provided by the temperature sensor S2, and the temperature rise width for the predetermined time is a predetermined temperature width. It may be determined that the temperature rises abnormally. Further, when it is determined that there is an abnormal temperature rise, a fixing device stop signal or an image forming operation stop signal by the printer PR may be output.

  In this example, a temperature sensor S2 is employed as a temperature detection unit for detecting the temperature of the end portion of the fixing roller. However, for example, when the fixing roller end temperature is determined according to the size of the recording medium and the number of recording media of that size, the demagnetizing coil controller CR2 records the recording medium size and its size. A function for calculating the temperature of the end of the fixing roller from the data on the number of passing sheets of the medium may be provided, and the function realization part may be used as a temperature detecting unit for detecting the temperature of the end of the fixing roller.

  In addition, when the temperature information from the temperature detection unit such as the temperature sensor S2 is used as a determination material for opening / closing control of the degaussing coil, the temperature serving as a criterion for determining that the degaussing coils 661 and 662 are closed from the open state and the degaussing coil By changing the temperature that is the criterion for determining whether to open from the beginning, it is possible to control the fixing roller end temperature more quickly. Specifically, it is possible to exemplify a case where the temperature that is a criterion for determining the degaussing coil from open to closed is set lower than the temperature that is the criterion for determining that the demagnetizing coil is closed to open. By doing so, the excessive temperature rise in the outer portion of the recording medium passage region can be further reduced.

  Here, the opening / closing control of the degaussing coil and its effect will be described with reference to FIG. The upper part of FIG. 6 shows a case where the demagnetizing coil is continuously closed without considering the temperature detected by the end temperature sensor S2 for opening and closing the demagnetizing coil. Regardless of the situation, if the degaussing coils 661 and 662 are continuously closed, the temperature at the end of the fixing roller is excessively lowered, which may affect the temperature of the recording medium passing area of the fixing roller 61. For example, the temperature of the recording medium passage area may be lower than the temperature at which the toner image can be fixed, resulting in poor fixing.

  Therefore, when the excessive temperature rise at the end of the fixing roller is large (when the temperature detected by the end temperature sensor S2 is equal to or higher than a preset temperature, or the number of sheets of a certain size of the recording medium passed is equal to or greater than the preset number. 6), when the closing time of the degaussing coils 661 and 662 is increased (the operation time is increased) and the excessive temperature rise at the end of the fixing roller is small (as shown in FIG. 6). 6 when the temperature detected by the internal temperature sensor S21 is lower than a predetermined set temperature, or when the number of sheets of a certain size of recording medium is smaller than the predetermined number), as shown in the lower part of FIG. If the closing time of the coils 661 and 662 is shortened (if the operation time is shortened), the action of the degaussing coil is strengthened when the excessive temperature rise is severe, and the action of the degaussing coil is weakened when the excessive temperature rise is small. And this While suppressing excessive Atsushi Nobori of the wearing roller ends, it is possible to satisfactorily perform also the fixing of the toner image to the recording medium. In addition, it is possible to cope with a multi-size recording medium and a difference due to the number of recording media to be fixed. While suppressing an excessive temperature rise at the end of the fixing roller, an excessive temperature drop at the end of the fixing roller can also be suppressed to increase thermal uniformity in the width direction of the fixing roller.

  The correspondence to the multi-size recording medium will be further described. For example, the target temperature (end temperature control setting temperature) of the fixing roller is set to the above-described temperature adjustment temperature (fixing temperature) for fixing the toner image. Separately, according to various recording medium sizes, the temperature is controlled so as not to hinder the fixing of the toner image onto the recording medium of the size while suppressing the excessive temperature rise, and the degaussing coil is controlled to open and close to the target temperature. Thus, it is possible to cope with a multi-size recording medium.

Regarding the correspondence to the difference due to the number of recording media to be fixed, for example, the target temperature of the fixing roller end (end temperature control setting temperature) is set to the temperature control temperature (fixing temperature) for fixing the toner image described above. Separately, according to the combination of various recording medium sizes and the number of fixing processes for each size of recording medium, the temperature is set at a temperature that does not hinder the fixing of the toner image onto the recording medium of the size while suppressing excessive temperature rise, By controlling opening and closing of the degaussing coil toward the target temperature, it becomes possible to cope with the difference depending on the number of recording media to be fixed.

  The temperature reduction range of the fixing roller 61 by the demagnetizing coils 661 and 662 corresponds to the range of magnetic flux generated by the degaussing coil, and has a wide range of inclination corresponding to the coil width (the longitudinal width of the fixing roller 61). For this reason, if the demagnetizing coil closing time (operation time) is shortened, it can affect a narrow range, and if the demagnetizing coil closing time (operation time) is lengthened, it can affect a wide range. By utilizing this fact, the set temperature for controlling the temperature at the end of the fixing roller can be overheated according to various recording medium sizes separately from the temperature control temperature (fixing temperature) for fixing the toner image described above. The temperature in the recording medium passage area is constant by controlling the opening / closing (operation time) of the degaussing coil toward the set temperature while setting the temperature at which the toner image is fixed on the recording medium of the size while suppressing it. Therefore, it becomes possible to cope with a multi-size recording medium.

  FIG. 7 shows an example of temperature distribution control of the fixing roller 61 by the degaussing coil. As shown in FIG. 7, when using a small size recording medium A smaller than the maximum size recording medium and a small size recording medium B smaller than the recording medium A, for example, the sizes of the degaussing coils 661 and 662 are matched to the small size recording medium B. When the toner image fixing process is performed on the small size recording medium B and the demagnetizing coils 661 and 662 are always closed, the temperature of the passing area of the small size recording medium B on the fixing roller 61 becomes the temperature adjustment temperature. Kept. However, if the demagnetizing coils 661 and 662 are always closed and the small-size recording medium A is passed, a temperature drop region is generated outside the recording medium B passage region and within the recording medium A passage region. Conversely, when the size of the degaussing coils 661 and 662 is adjusted to the small size recording medium A, when passing through the small size recording medium B, it is excessively increased outside the passing area of the recording medium B and into the passing area of the recording medium A. A temperature region will be generated.

  However, the size of the degaussing coils 661 and 662 is adjusted to the recording medium B by controlling the open / closed state of the degaussing coils 661 and 662 to a preset temperature for fixing roller end temperature control according to the recording medium size. Even if it is determined according to the recording medium A, it is possible to cope with both size recording media. Specifically, the fixing roller end temperature control set temperature (target temperature) is set higher when the small size recording medium A is passed than when the small size recording medium B is passed. It should be noted that by setting the fixing roller end temperature control set temperature more in accordance with the size of the recording medium, it is possible to deal with a larger number of recording media.

  As described above, the demagnetizing coil controller CR2 is determined in accordance with the temperature information input from the end temperature sensor S2 and the recording medium size in advance and stored, as described above. Based on the set temperature for fixing roller end temperature control, the switch SW1 and SW2 for each demagnetizing coil in the switching circuit C2 are controlled to open and close, thereby controlling the operation time of each demagnetizing coil. Control the temperature to the set temperature.

FIG. 4 exemplifies various sizes of recording media and the passing area widths of the recording media in the fixing roller 61. In FIG. 4, “B5T” indicates a B5 size recording medium and its passing area width when it is passed through the fixing device in the vertical direction (in the longitudinal direction).
Similarly, “A4T” indicates an A4 size recording medium that passes vertically and its passing area width, “B4T” indicates a B4 size recording medium that passes vertically and its passing area width, and “B5Y”. Indicates the B5 size recording medium to be passed horizontally (in the lateral direction) and its passing area width, “A4Y” indicates the A4 size recording medium to be passed horizontally and its passing area width, and “A3T” is 4A shows an A3 size recording medium to be passed vertically and its passing area width.

  In the example shown in FIG. 4, the degaussing coils 661 and 662 are exciting coils 65 of the electromagnetic induction heat generating layer 613 at the end of the fixing roller outside the passing area of the minimum size recording medium B5T among the recording media to be subjected to toner image fixing processing. It is provided so that heat generation by the magnetic flux can be suppressed.

The temperature sensor S2 may be provided so as to be able to detect the temperature of the end of the fixing roller outside the passing area of the minimum size recording medium B5T. Here, as shown in FIG. In order to cope with it more reliably, it is provided at the end of the fixing roller outside the area where the large-size recording medium A4Y passes and in the area including the pressure nip N between the fixing roller 61 and the pressure roller 62. .
Note that when fixing a toner image on a recording medium of the maximum size among the recording media targeted for toner image fixing processing, the demagnetizing coils 661 and 662 may be left open without particularly considering the fixing roller end temperature. Good.

(2-6) Operation example of control unit Cont including degaussing coil opening / closing control by degaussing coil control unit CR2 (see FIG. 8)
FIG. 8 is a flowchart showing an outline of an operation example of the control unit Cont including degaussing coil opening / closing control by the degaussing coil control unit CR2.

  In the control shown in FIG. 8, a recording sheet is used as a recording medium, and the minimum size recording sheet among the recording sheets targeted for toner image fixing processing is B5T (see FIG. 4). The recording sheet size here is the size of the recording sheet width that is orthogonal to the sheet passing direction in the fixing device 6 as described in connection with FIG.

As shown in FIG. 4, the demagnetizing coils 661 and 662 are provided to face the exciting coil 65 on the outer side of the fixing roller 61 on the passing area of the minimum size recording paper (B5T).
The end temperature sensor S2 is provided on a portion of the fixing roller 61 outside a region where the large-size recording paper A4Y (A3T) passes and in a region where the pressure nip N of the rollers 61 and 62 is formed.

  The demagnetizing coil controller CR2 stores preset temperatures for fixing roller end temperature control predetermined for each recording paper size as shown in the following table. When the temperature detected by the temperature sensor S2 exceeds the set temperature, the control unit CR2 closes the demagnetizing coils 661 and 662, and when the temperature detected by the temperature sensor S2 is equal to or lower than the set temperature, the demagnetizing coils 661 and 662 are set. Open. Note that the temperature adjustment temperature at the center of the fixing roller directed by the temperature adjustment control unit CR1 is 180 ° C. in this example.

Recording paper size W Setting temperature for fixing roller end temperature control W ≧ A4Y 200 ° C.
A4Y>W> A4T 170 ° C
W = A4T 160 ° C
A4T> W 130 ° C

Initially, the degaussing coil is left open (step S100).
Next, the size of the recording paper on which the toner image is fixed is determined. If the size is A4Y, the set temperature is set to 200 ° C. (steps S200 and S300).
When the size is A4Y>W> A4T (accordingly, B4T or B5Y), the set temperature is set to 170 ° C. (steps S400 and S500).
When the size is A4T, the set temperature is set to 160 ° C. (steps S600 and S700). When the size is W <A4T (accordingly, B5T), the set temperature is set to 130 ° C. (steps S800 and S900).

  When the set temperature corresponding to the size of the recording paper used is set, the fixing roller end temperature detected by the temperature sensor S2 is compared with the set temperature, and the fixing roller end detected by the temperature sensor S2 is compared. If the part temperature exceeds the set temperature, the switches SW1 and SW2 in the switching circuit C2 are closed and the degaussing coils 661 and 662 are closed to keep the fixing roller end temperature low (steps S1000 and S1100).

  When the fixing roller end temperature detected by the temperature sensor S2 is equal to or lower than the set temperature, the switches SW1 and SW2 in the switching circuit C2 are opened, and the degaussing coils 661 and 662 are opened (steps S1000 and S1200).

In this state, the printing operation is started, and a predetermined number of sheets are printed (steps S1300 and S1400).
In this control, the set temperature for controlling the end temperature of the fixing roller is determined according to the recording medium size. In addition to the recording medium size, one or more of the recording medium conveyance speed, printing mode, and the like are also taken into consideration. May be determined.

[4] Another example of fixing device (see FIG. 9)
FIG. 9 shows another example of the fixing device according to the present invention. The fixing device 6 ′ shown in FIG. 9 detects the temperature at the end of the fixing roller indirectly by placing the temperature sensor S2 on the end of the pressure roller 62 in the fixing device 6 shown in FIG. It is a thing. The other points are the same as those of the fixing device 6, and the same parts and portions as those of the fixing device 6 are denoted by the same reference numerals as those of the fixing device 6.

  When the end temperature sensor S2 is provided at the end of the heating roller 61 in order to cope with the end excessive temperature rise of the fixing roller 61, the demagnetizing coils 661 and 662 can be shortened in a short time according to the ripple due to temperature adjustment to the fixing temperature. May be opened and closed. If the degaussing coil is opened and closed in a short time, it may cause image noise and may adversely affect the control of the exciting coil 65. In addition, when a high-voltage relay circuit is used, the load on the relay increases.

  On the other hand, if the temperature sensor S2 is provided for the pressure roller 62 and the opening / closing control of the demagnetizing coils 661 and 662 is performed, the temperature ripple is equalized when heat is transferred from the fixing roller 61 to the pressure roller 62. The demagnetizing coil is not opened and closed in a short time, and only large temperature fluctuations due to continuous printing can be captured, so that noise generation and load on the relay can be reduced.

  Further, since a temperature control temperature sensor and a thermostat are usually disposed around the fixing roller 61, it may be difficult to dispose the end temperature sensor S2. However, the disposition of the temperature sensor S2 with respect to the pressure roller may be difficult. Easy to spot. Further, when a contact sensor having excellent cost and sensitivity is arranged as the end temperature sensor, the influence on the image can be reduced.

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or printer, a fixing device for heating and fusing an unfixed toner image formed on a recording medium, and fixing the image to the recording medium, and an image including the fixing device. It can be used to provide a forming apparatus.

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 right side in FIG. 2. It is a figure which shows the arrangement | positioning relationship between an exciting coil and a degaussing coil, the passage area of a recording medium, etc. FIG. 2 is a block diagram illustrating an outline of a control circuit of the image forming apparatus illustrated in FIG. 1. It is a figure which shows the example of switching control of a degaussing coil compared with the past. It is a figure which shows the example of temperature distribution control on the fixing roller by a demagnetizing coil. 6 is a flowchart illustrating an outline of an example of an operation of an image forming apparatus control unit including an example of opening / closing control of a degaussing coil. FIG. 6 is a cross-sectional view showing a main part of another example of the fixing device according to the present invention.

Explanation of symbols

PR 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 Opposing roller 4 Intermediate transfer belt 5 Secondary transfer roller 8 Cleaner 9 Timing roller pair P Recording medium

6 Fixing device 6 'Fixing device 61 Fixing roller 611 Support layer 612 Heat insulation layer 613 Electromagnetic induction heat generation layer 614 Elastic layer 615 Release layer 62 Pressure roller 621 Core metal 622 Layer 623 on core metal outer periphery 623 Release layer N Pressure nip 63 Heat equalizing roller 631 Heater lamp 60 Magnetic flux generator 64 Coil bobbin 641 Bobbin window 65 Exciting coil 67 Main core 68 Bottom core 661, 662 Demagnetizing coil S1 Temperature control temperature sensor S2 End temperature sensor Cont Control unit C1 Excitation coil drive circuit CR1 Temperature control unit C2 Switching circuit SW1, SW2 Switch CR2 Demagnetizing coil control unit

Claims (11)

Flux comprising a rotatable fixing roller having an electromagnetic induction heat generating layer, a rotatable pressure roller to be pressed against the fixing roller, an exciting coil for generating a magnetic flux to heat the electromagnetic induction heating layer of the fixing roller The magnetic induction heat generating layer of the fixing roller is heated by the magnetic flux generator, and the recording medium holding the toner image is passed through the nip portion between the fixing roller and the pressure roller. An image can be fixed on the recording medium, and three or more types of recording media having different sizes in a direction orthogonal to the passing direction of the recording medium can be passed through the nip portion to fix the toner image on the recording medium. A fixing device that can
A temperature control temperature sensor for detecting the temperature of the passing area of the minimum size recording medium in the fixing roller;
Excitation for controlling the excitation coil based on the temperature of the passage area detected by the temperature adjustment temperature sensor so that the temperature of the passage area is set to a predetermined temperature adjustment temperature required for the toner image fixing process. A coil controller;
A degaussing coil disposed outside the passing area width of the recording medium of the smallest size among the recording media to be subjected to toner image fixing processing and arranged adjacent to the end of the exciting coil in accordance with the passing area width of the recording medium having a predetermined size. When,
A switching circuit for opening and closing the demagnetizing coil;
A degaussing coil controller that controls opening and closing of the degaussing coil by the switching circuit;
An end temperature sensor for detecting the temperature of the end of the fixing roller outside the passing area width of the minimum size recording medium,
The demagnetizing coil control unit determines the fixing roller end temperature for each size of the recording medium to be subjected to toner image fixing processing based on the fixing roller end temperature detected by the end temperature sensor . The fixing device controls the opening and closing of the degaussing coil by controlling the switching circuit so as to go to a fixing roller end temperature control set temperature for suppressing excessive temperature rise . Wherein said end portion temperature sensor for detecting the fixing roller end portion temperature fixing device according to claim 1, characterized in that the臨設the fixing roller end portion. Wherein said end portion temperature sensor for detecting the fixing roller end portion temperature fixing device according to claim 1, characterized in that the臨設to an end of the pressure roller which is pressed against the fixing roller end portion.   The end temperature sensor is provided so as to detect a temperature of a portion of the fixing roller in a region outside a passing region of a maximum size recording medium in a toner image fixing process target recording medium and in the nip region. Item 4. The fixing device according to Item 1, 2 or 3. The demagnetizing coil control unit controls the switching circuit so that the demagnetizing coil is closed when the temperature detected by the end temperature sensor exceeds the fixing roller end temperature control set temperature. 5. The fixing according to claim 1, wherein the switching circuit is controlled so that the demagnetizing coil is opened when a temperature detected by a temperature sensor is equal to or lower than a fixing roller end temperature control set temperature. apparatus. The demagnetizing coil control unit controls the switching circuit so that the demagnetizing coil is closed when the temperature detected by the end temperature sensor starts to rise to a predetermined first temperature or higher, and the end portion When the temperature detected by the temperature sensor begins to cooling to a second temperature below a temperature higher than a predetermined first temperature, the claim 1 for controlling the switching circuit so that the degaussing coil is opened for 4 The fixing device according to any one of the above. The degaussing coil control unit, said end of the temperature detected by the temperature sensor, when the rise in the predetermined time a predetermined become more predetermined rise, according to claim 1, 2 determines that an abnormality has occurred, The fixing device according to 3, 4, or 6.   2. The fixing roller end temperature control set temperature is a temperature calculated based on a size of a recording medium subject to toner image fixing processing and a number of recording media on which toner image fixing processing is performed with the recording medium of the size. The fixing device according to claim 7.   The fixing device according to claim 1, wherein the fixing roller end temperature control set temperature is different from a temperature adjustment temperature of the fixing roller for fixing a toner image. The fixing device according to claim 1, wherein a temperature-uniforming member is disposed in contact with the surface of the fixing roller or the surface of the pressure roller . An image forming apparatus that forms an electrostatic latent image on an electrostatic latent image carrier, develops the electrostatic latent image to form a toner image, transfers the toner image to a recording medium, and fixes the toner image with a fixing device. The image forming apparatus according to claim 1 , wherein the fixing device is a fixing device according to claim 1 .