JP2009199016A - Heat-fixing apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-fixing apparatus preventing overheating of a fixing member without causing the enlargement of the apparatus, and an image forming apparatus. <P>SOLUTION: The IH-type heat-fixing apparatus 140 includes a plurality of magnetic flux shielding plates 204 supported between a fixing roller 141 and exciting coils 201 turnably around a rotation axis parallel with a rotation axis of the fixing roller 141. The magnetic flux shielding plates 204 are turned according to the size of paper passed to the fixing apparatus 140 to shield magnetic flux generated by the exciting coils 201. Overheating of a paper non-passing part of the fixing roller 141 is thereby prevented. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a heat fixing device and an image forming apparatus, and more particularly, to a technique that achieves both the elimination of problems caused by overheating of a fixing member in an IH type fixing device and the miniaturization of the fixing device.

  In recent years, an IH heater has been used as a heat fixing device of an image forming apparatus for the purpose of power saving from the viewpoint of environmental problems and cost reduction. The IH heater electromagnetically heats a fixing member (belt or roller) having a low heat capacity by an exciting coil. In this way, the time required for warming up can be shortened.

  However, since the fixing member having a low heat capacity has a low heat conduction speed, a portion of the fixing member through which the sheet does not pass is overheated (for example, 260 ° C. or more) when small-size paper is continuously passed. When large-size paper is passed in this state, high-temperature offset and gloss unevenness due to toner overmelting occur. Further, when the fixing member is further overheated, the PFA (Tetrafluoroethylene-perfluoroalkylvinyl ether copolymer) tube covering the fixing roller and the pressure roller may be melted or broken.

In order to solve such a problem, for example, a technique for adjusting the magnetic flux density by inserting and removing a magnetic member, a magnetic flux attenuation coil, and a magnetic flux shielding plate in the heating roller has been proposed. In this way, electromagnetic induction heating in a portion where the small size paper of the fixing member does not pass can be reduced, so that a problem due to overheating of the portion can be solved.
Japanese Patent Laid-Open No. 9-171889 Japanese Patent Laid-Open No. 10-74009

  However, in order to insert / remove the magnetic member etc. into / from the heating roller, a space for moving the magnetic member etc. and a drive source for moving the magnetic member, etc. are required, so it is inevitable to enlarge the device There is a problem that the manufacturing cost increases.

  SUMMARY An advantage of some aspects of the invention is that it provides a heat fixing apparatus and an image forming apparatus that prevent overheating of a fixing member without causing an increase in the size of the apparatus. .

  In order to achieve the above object, a heat fixing apparatus according to the present invention is a heat fixing apparatus that heats and fixes a toner image onto a recording sheet that is passed through a fixing member that has been electromagnetically heated by an excitation coil. A plurality of narrow and long magnetic plates are arranged in the gap between the coil and the fixing member depending on the size of the recording sheet. It is characterized by being arranged so as to be rotatable in a state of being directed in an orthogonal direction and having an interval that does not interfere with each other during rotation.

  In particular, the larger the size of the recording sheet to be rotated and the rotation driving means for rotating the magnetic plate, the larger the interval between the adjacent magnetic plates, and the smaller the size of the recording sheet to be passed, And a control means for controlling the rotation drive means so as to reduce the interval, the density of the magnetic flux generated by the exciting coil in the non-sheet passing portion of the fixing member is reduced by the plurality of magnetic plates. Overheating of the fixing member can be prevented without increasing the size of the fixing member.

  In the heat fixing device according to the present invention, the magnetic plate is arranged so that the width of the magnetic plate decreases in the longitudinal direction from one end to the other end, and the end having the smaller width faces the center of the fixing member. It is characterized by that. By doing so, the non-sheet passing portion is heated to such an extent that it does not overheat, and the temperature distribution of the sheet passing portion is made uniform, thereby preventing image quality deterioration due to uneven fixing.

  In addition, a sensor for measuring the temperature of the fixing member is provided, and the control means fixes the fixing gap as the temperature of the fixing member decreases even if the size of the recording sheet to be passed is the same. The rotational drive means is controlled so that the gap between the magnetic plates becomes smaller as the temperature of the member becomes higher, or a counter that counts the number of continuously passing sheets is provided. If the rotation driving means is controlled so as to rotate the magnetic plate, the fixing member can be reliably prevented from overheating.

  An image forming apparatus according to the present invention includes the heat fixing device according to the present invention. In this way, overheating of the fixing member can be prevented without increasing the size of the apparatus.

  Hereinafter, embodiments of a heat fixing device and an image forming apparatus according to the present invention will be described with reference to the drawings.

[1] Configuration of Image Forming Apparatus First, the configuration of the image forming apparatus according to the present embodiment will be described.

  FIG. 1 is a diagram illustrating a main configuration of the image forming apparatus according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 is a so-called tandem image forming apparatus, and includes image forming units 100 </ b> C to 100 </ b> K, a control unit 110, an intermediate transfer belt 120, a secondary transfer roller 121, and a paper feeding unit 130. A fixing unit 140 and a paper discharge tray 150 are provided.

  The image forming units 100 </ b> C to 100 </ b> K form toner images of cyan (C), magenta (M), yellow (Y), and black (K), respectively, and transfer them onto the intermediate transfer belt 120. Since the image forming units 100C to 100K have the same configuration, the image forming unit 100K will be described as an example.

  The image forming unit 100K includes a photosensitive drum 101, a charger 102, an exposure device 103, a developing device 104, and a primary transfer roller 105. The photoconductor drum 101 has a photoconductor on its outer peripheral surface, and is driven to rotate in the direction of the arrow by a drive motor (not shown).

  The charger 102 uniformly charges the surface of the photosensitive drum 101. The exposure device 103 includes a semiconductor laser. Under the control of the control unit 110, the outer peripheral surface of the photosensitive drum 101 is exposed with a laser beam to form an electrostatic latent image.

  The developing device 104 supplies toner onto the outer peripheral surface of the photosensitive drum 101 to visualize the electrostatic latent image into a toner image. The primary transfer roller 105 transfers the toner image formed on the outer peripheral surface of the photosensitive drum 101 onto the intermediate transfer belt 120 (primary transfer). The toner remaining on the photosensitive drum 101 after the primary transfer is removed by a cleaner (not shown).

  The same processing is also executed by the image forming units 100C to 100Y, and the toner images are sequentially primary-transferred in sequence so that the toner images overlap on the intermediate transfer belt 120. When the amount of toner held in the developing device 104 becomes a predetermined amount or less, the toner is replenished from a toner bottle (not shown).

  The image forming units 100C to 100Y and the toner bottle can be exchanged. In addition, an IC chip is mounted on each of the image forming units 100C to 100Y and the toner bottle. The image forming apparatus 1 detects the mounting state and the replacement state of the image forming units 100C to 100Y and the toner bottle by wired or wireless communication with the IC chip.

  The intermediate transfer belt 120 is made of, for example, PET (polyethylene terephthalate) or PVDF (polyvinylidene fluoride). The intermediate transfer belt 120 is given an appropriate tension by a tension roller and is circulated by a driving roller. As a result, the intermediate transfer belt 120 conveys the toner image to the secondary transfer position.

  The paper feed unit 130 picks up the recording sheets P stored in the paper feed cassette one by one by a pickup roller and carries them out to the secondary transfer position. The secondary transfer roller 121 transfers the toner image on the intermediate transfer belt 120 onto the recording sheet P. The toner remaining on the intermediate transfer belt 120 after the secondary transfer is scraped off by a cleaner blade and stored in a waste toner box.

  The fixing unit 140 includes a fixing roller 141 and a pressure roller 142. The fixing roller 141 is heated by a heater (not shown) to melt the toner on the recording sheet P. The pressure roller 142 presses the melted toner onto the recording sheet P by sandwiching the recording sheet P with the fixing roller 141. Thereafter, the recording sheet P is discharged to the paper discharge tray 150.

[2] Configuration of Fixing Device 140 Next, the configuration of the fixing device 140 will be described.

  FIG. 2 is a diagram illustrating a main configuration of the fixing device 140. As shown in FIG. 2, the fixing device 140 is an IH type heat fixing device, and includes a fixing roller 141, a pressure roller 142, an exciting coil 201, a ferrite core 202, a bottom core 203, a magnetic flux shielding plate 204, and a non-contact type. A thermistor 205 is provided.

  The fixing roller 141 has a diameter of 40 mm (hereinafter, the diameter Rmm is represented as φR), a roller width (rotating shaft), in which the outer peripheral surface of a SUS (Stainless Used Steel) core metal 141a is covered with a silicone sponge layer 141b having a thickness of 10 mm. (Length in direction) 320 mm. The outer peripheral surface of the silicone sponge layer 141b is further covered with a heating belt 141c.

  The heating belt 141c is formed by sequentially laminating a heat resistant elastic layer and a heat resistant release layer on a Ni belt. The thickness of the Ni belt is 40 μm. The heat-resistant elastic layer is made of silicone rubber and has a thickness of 200 μm. The heat-resistant release layer is a PFA tube having a thickness of 30 μm, and prevents the toner and the like from adhering to the surface of the heating belt 141c.

  The exciting coil 201 is formed by winding 10 litz wires bundled with 114 copper wires of φ0.15 mm in the axial direction of the fixing roller 141 for 10 turns. The exciting coil 201 generates a magnetic flux around the AC coil when energized.

  The ferrite core 202 is made of MnZn-based ferrite and is disposed to face the fixing roller 141 with the exciting coil 201 interposed therebetween. The ferrite core 202 is provided so that the magnetic flux generated by the exciting coil 201 passes through the heating belt 141c. The skirt core 203 is also made of MnZn-based ferrite and is oriented so that the magnetic flux leaking from the end of the ferrite core 202 passes through the heating belt 141c.

  The pressure roller 142 is formed by sequentially coating a heat resistant elastic layer 142b and a heat resistant release layer 142c on a cored bar 142a. The cored bar 142a is a φ35 iron pipe made of STKM (Carbon steel Tubes for Machine Structural Purpose). The heat-resistant elastic layer 142b has a two-layer structure in which a silicone rubber layer is laminated on a silicone sponge layer. The heat-resistant release layer 142c is made of a PFA tube.

  The pressure roller 142 is pressed against the fixing roller 141 with a pressing force of about 500 N, and a fixing nip portion having a width of about 12 mm in the sheet conveyance direction is secured. The fixing roller 141 and the pressure roller 142 are always driven to rotate during fixing.

  The magnetic flux shielding plate 204 is made of ferrite having a high magnetic permeability and a large specific resistance, and controls the magnetic flux density on the heating belt 141c by shielding the magnetic flux generated by the exciting coil 201. The non-contact thermistor 205 measures the temperature of the heating belt 141c. Based on the measurement result, the temperature of the heating belt 141c is adjusted to about 180 ° C. during fixing.

[3] Magnetic flux shielding plate 204
Next, the magnetic flux shielding plate 204 will be described.

  As shown in FIG. 2, the magnetic flux shielding plate 204 is disposed along the outer peripheral surface of the fixing roller 141 so that the central angle around the rotation axis of the fixing roller 141 is about 115 °. The magnetic flux shielding plates 204 are arranged from the both ends of the fixing roller 14 toward the central portion in the direction of the rotation axis, and 10 pieces are arranged along the rotation axis. The magnetic flux shielding plates 204 are supported so as to be rotatable about a rotation axis parallel to the rotation axis of the fixing roller.

  FIG. 3 is a view showing the shape of the magnetic flux shielding plate 204. As shown in FIG. 3, the magnetic flux shielding plate 204 has a substantially trapezoidal shape in plan view, and the size in the longitudinal direction is 40 mm. The larger width is 8 mm and the smaller width is 3 mm, and the width is reduced at a constant rate from the position of 10 mm in the longitudinal direction to the small width end.

  A pin 301 and a rotation support shaft 302 are fixed to a large end of the magnetic flux shielding plate 204, and the magnetic flux shielding plate 204 is rotationally driven by a drive mechanism described below.

[4] Driving mechanism of magnetic flux shielding plate 204 Next, the driving mechanism of the magnetic flux shielding plate 204 will be described. The magnetic flux shielding plates 204 are driven by four drive mechanisms, five by five. Since the four drive mechanisms all have a common structure, only one drive mechanism will be described here.

  4A and 4B are diagrams showing a driving mechanism of the magnetic flux shielding plate 204, where FIG. 4A shows the posture when passing large-size paper, and FIG. 4B shows the posture when passing small-size paper. In FIG. 4, a configuration in which three magnetic flux shielding plates 204 are driven is shown in consideration of easy viewing, but even when five magnetic flux shielding plates 204 are driven. The structure of the drive mechanism is almost the same.

  As shown in FIG. 4, the drive mechanism 4 for the magnetic flux shielding plate 204 includes a drive motor 401, a drive crank 402 and a lever 403. As shown in FIG. 4, the drive motor 401 is a so-called stepping motor and pivotally supports the drive crank 402. One end of the drive crank 402 is pivotally supported by the drive motor 401, and a pin 402a is fixed to the other end.

  The lever 403 is provided with guide grooves 403a and 403b. When the drive motor 401 rotates the drive crank 402, the pin 402a of the drive crank 402 moves along the guide groove 403b and moves the lever 403.

  Each of the rotation support shafts 302 of the magnetic flux shielding plate 204 is supported by a holder (not shown). Further, the pins 301 of the magnetic flux shielding plate 204 move along the corresponding guide grooves 403a.

  Therefore, when the drive motor 401 rotates the drive crank 402, the lever 403 moves, and the pin 301 is moved along the guide groove 403a. On the other hand, the rotation support shaft 302 of the magnetic flux shielding plate 204 does not move, and the magnetic flux shielding plate 204 is rotationally driven by changing the positional relationship between the pin 301 and the rotation support shaft 302.

  In this case, the magnetic flux shielding plate 204 rotates by an angle corresponding to the number of pulses input to the drive motor 401. That is, the attitude of the magnetic flux shielding plate 204 is controlled by the number of input pulses in the drive mode 401.

[4] Attitude Control of Magnetic Flux Shielding Plate 204 Next, attitude control of the magnetic flux shielding plate 204 will be described.

  The magnetic flux shielding plate 204 changes the magnetic flux density distribution on the heating belt 141c by changing the posture according to the width of the paper S passed through the fixing nip, that is, the size of the fixing roller 141 in the rotation axis direction. adjust.

(1) When Large Size Paper is Passed The attitude control of the magnetic flux shielding plate 204 when passing large size paper will be described. Here, the large size paper refers to a paper of a size that passes through the entire rotation axis direction of the fixing roller 141, and is, for example, A4 horizontal.

  As shown in FIG. 2, when passing large-size paper, the magnetic flux shielding plate 204 is controlled in posture so that the main surface is parallel to the radial direction of the fixing roller 141. In other words, the posture of the magnetic flux shielding plate 204 is controlled so that the surface including the main surface thereof is orthogonal to the outer peripheral surface closest to the fixing roller 141.

  If the magnetic flux shielding plate 204 takes such a posture, the magnetic flux generated by the exciting coil 201 is not shielded, so that the entire area of the heating belt 141c can be heated by electromagnetic induction.

  FIG. 5 is a diagram showing a positional relationship between the passing position of the large size paper and the magnetic flux shielding plate 204. Since the positional relationship between the passing position of the large size paper and the magnetic flux shielding plate 204 is the same at any end portion of the fixing roller 141, only the one end portion of the fixing roller 141 is shown in FIG. 5. ing.

  As shown in FIG. 5, when the large size paper 501 is passed, the magnetic flux shielding plate 204 does not shield the magnetic flux, so that the fixing roller 141 is heated by electromagnetic induction over the entire region in the rotation axis direction. Thus, heat fixing is performed over the entire width of the large size paper 501.

(2) When Small Size Paper is Passed Next, attitude control of the magnetic flux shielding plate 204 when passing small size paper will be described. Here, the small size paper refers to a paper of a size that passes only through the central portion of the fixing roller 141 in the rotation axis direction, and is, for example, A4 vertical.

  FIG. 6 is a diagram illustrating a state of the fixing device 140 when a small-size sheet is passed. As shown in FIG. 6, when passing small size paper, the magnetic flux shielding plate 204 is controlled in posture so that the main surface is orthogonal to the radial direction of the fixing roller 141. In other words, the posture of the magnetic flux shielding plate 204 is controlled so that the surface including the main surface is parallel to the tangential direction of the outer peripheral surface closest to the fixing roller 141.

  If the magnetic flux shielding plate 204 takes such a posture, the magnetic flux generated by the exciting coil 201 is shielded. For this reason, electromagnetic induction heating is limited in the region immediately below the magnetic flux shielding plate 204 of the fixing roller 141 when viewed from the exciting coil 201.

  Note that, as described above, the magnetic flux shielding plate 204 has a trapezoidal shape and contracts as it approaches the center of the fixing roller 141. The degree to which the electromagnetic induction heating is limited becomes smaller as the width of the magnetic flux shielding plate 204 is smaller. Therefore, the temperature is increased by electromagnetic induction heating as it approaches the center from the end of the fixing roller 141 in the rotation axis direction. As a result, the non-sheet passing portion temperature is suppressed to 220 ° C. or lower.

  FIG. 7 is a diagram showing the positional relationship between the small size paper passing position and the magnetic flux shielding plate 204. Since the positional relationship between the small-size paper passing position and the magnetic flux shielding plate 204 is also the same at any end of the fixing roller 141, FIG. 7 also shows one end of the fixing roller 141 as in FIG. This relationship is shown only for.

  As shown in FIG. 7, when the small-size paper 701 is passed, the magnetic flux shielding plate 204 shields the magnetic flux, so that the fixing roller 141 mainly performs electromagnetic induction heating at the paper passing position of the small-size paper 701. . This prevents the non-sheet passing position of the small size paper 701 from overheating.

(3) When passing medium-size paper Next, the attitude control of the magnetic flux shielding plate 204 when passing the medium-size paper will be described. Here, the medium size paper refers to a medium size paper between the large size paper and the small size paper, and is, for example, B5 horizontal.

  When passing the medium size paper, the magnetic flux shielding plate 204 is controlled so as to be in an intermediate position between the posture when passing the large size paper and the posture when passing the small size paper.

  FIG. 8 is a diagram showing the positional relationship between the passing position of medium-size paper and the magnetic flux shielding plate 204. Also in FIG. 8, the positional relationship between the sheet passing position and the magnetic flux shielding plate 204 is shown only for one end of the fixing roller 141.

  As shown in FIG. 8, when the medium-size paper 801 is passed, the magnetic flux shielding plate 204 only partially shields the magnetic flux, so that the fixing roller 141 is heated by electromagnetic induction over the entire region in the rotation axis direction. . However, immediately below the magnetic flux shielding plate 204, electromagnetic induction heating of the fixing roller 141 is limited according to the width of the magnetic flux shielding plate 204.

  As a result, heat fixing is performed over the entire width of the medium-size paper 801, and at the same time, overheating of the non-sheet passing portion of the medium-size paper 801 can be prevented.

  In addition, by adjusting the posture (angle) of the magnetic flux shielding plate 204, it is possible to appropriately heat and fix the medium size paper other than the B5 horizontal, and at the same time, to prevent the non-sheet passing portion of the fixing roller 141 from being heated. it can.

[5] Control unit 110
Next, the control unit 110 will be described.

(1) Configuration of Control Unit 110 First, the configuration of the control unit 110 will be described.

  FIG. 9 is a diagram illustrating a configuration of the control unit 110. As shown in FIG. 9, the control unit 110 includes a central processing unit (CPU) 901, a random access memory (RAM) 902, a read only memory (ROM) 903, an operation panel 904, a network interface card (NIC) 905, and an I / O. An O (Input / Output) controller 906 is connected by an internal bus 907.

  The I / O controller 906 is connected to a fixing roller driving motor 909, a magnetic flux shielding plate driving motor 910, and an IH inverter 911 via a dedicated bus 908.

  The CPU 901 reads the control program stored in the ROM 903, which is a nonvolatile memory, into the RAM 902 and executes it. The CPU 901 receives a print job via the operation panel 904 or the NIC 905.

  The CPU 901 controls the fixing roller driving motor 909, the magnetic flux shielding plate driving mode 910 and the IH inverter 911 via the I / O controller 906, rotationally drives the fixing roller 141, adjusts the angle of the magnetic flux shielding plate 204, and fixes. The temperature of the roller 141 is adjusted.

(2) Operation of Control Unit 110 Next, the operation of the control unit 110 will be described.

  FIG. 10 is a flowchart showing the operation of the control unit 110. As shown in FIG. 10, the control unit 110 first receives a print job from the operation panel 904 or the NIC 905 (S1001), and refers to the paper size specified in the print job (S1002).

  If the paper size is A4 horizontal (S1003: Yes), the rotation angle of the magnetic flux shielding plate 204 is determined according to A4 horizontal (S1004). If the paper size is B5 width (S1005: Yes), the rotation angle of the magnetic flux shielding plate 204 is determined according to B5 width (S1006). If the paper size is A4 vertical (S1007: Yes), the rotation angle of the magnetic flux shielding plate 204 is determined in accordance with the A4 vertical (S1008).

  When the rotation angle is determined in accordance with the paper size, the magnetic flux shielding plate 204 is rotated to the position of the rotation angle (S1009), and the fixing roller 141 is heated by controlling the IH inverter 911 to generate magnetic flux from the excitation coil 201. While (S1010), the toner image is heated and fixed on the paper (S1011).

  If the paper size designated in the print job is neither A4 horizontal, B5 horizontal, or A4 vertical, a paper size error is notified on the operation panel 904 (S1012). Further, this paper size error may be recorded in a log.

[6] Modifications Although the present invention has been described based on the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments, and the following modifications can be implemented. .

  (1) In the above embodiment, a case has been described in which the posture (angle) of the magnetic flux shielding plate 204 is adjusted according to the size of the paper designated in the print job, but the present invention is not limited to this. Needless to say, the following may be used instead of or together with this.

  That is, when the paper size is other than a large size, the temperature of the non-sheet passing portion of the fixing roller 141 may be detected by the non-contact thermistor 205, and the posture of the magnetic flux shielding plate 204 may be adjusted according to the detected temperature. . FIG. 11 is a flowchart showing the attitude control of the magnetic flux shielding plate based on the fixing roller temperature. As shown in FIG. 11, when the printing process is started, the controller 110 measures the temperature of the fixing roller 141 with the non-contact thermistor 205 (S1101).

  If the temperature of the fixing roller 141 is higher than the predetermined upper limit temperature (S1102: Yes), the magnetic flux shielding plate 204 is slightly laid on the outer peripheral surface of the fixing roller 141 to strengthen the magnetic flux shielding and suppress the electromagnetic induction heating. (S1103). If the temperature of the fixing roller 141 is lower than the predetermined lower limit temperature (S1104: Yes), the magnetic flux shielding plate 204 is slightly raised from the outer peripheral surface of the fixing roller 141 to weaken the magnetic flux shielding and increase the electromagnetic induction heating. (S1105).

  When the temperature of the fixing roller 141 is between the upper limit temperature and the lower limit temperature (S1104: No), the attitude of the magnetic flux shielding plate 204 is controlled to an angle according to the paper size (S1106). Thereafter, it is confirmed whether or not the printing process has ended. If the printing process has not ended (S1107: No), the process proceeds to step S1101, and the above process is repeated.

  Further, since the temperature rise in the non-sheet passing portion changes according to the continuous sheet passing number (continuous printing number), the posture of the magnetic flux shielding plate 204 may be adjusted according to the continuous sheet passing number. FIG. 12 is a flowchart showing the attitude control of the magnetic flux shielding plate based on the continuous sheet passing number. As shown in FIG. 12, the control unit 110 first controls the attitude of the magnetic flux shielding plate 204 at an angle according to the paper size specified in the print job (S1201).

  Next, the control unit 110 initializes the value of the variable N for counting the number of continuous prints to zero (S1202). Thereafter, each time one sheet is printed according to the print job (S1203: Yes), the value of the variable N is incremented by 1 (S1204). When the value of the variable N becomes 100 (S1205: Yes), the magnetic flux shielding plate 204 is laid on the fixing roller 141 by a predetermined angle from the angle matched to the paper size (1206).

  Accordingly, the shielding of the magnetic flux is strengthened and the electromagnetic induction heating is suppressed, so that the fixing roller 141 is prevented from overheating. Thereafter, when the printing process according to the print job is finished (S1207: Yes), the above process is finished.

  When it is known in advance that the fixing roller 141 is overheated when the number of continuous paper passes exceeds 100, the magnetic flux shielding plate 204 can be obtained as described above without performing temperature measurement using a non-contact thermostat. Can be controlled properly.

  In this case, the continuous sheet passing number for controlling the posture of the magnetic flux shielding plate 204 may be other than 100 sheets. Alternatively, the attitude of the magnetic flux shielding plate 204 may be controlled in multiple stages, for example, the attitude may be controlled in two stages of 100 sheets and 200 sheets. As described above, the posture of the magnetic flux shielding plate can also be appropriately controlled by estimating the temperature of the fixing roller 141 from the number of continuous sheets.

  (2) In the above embodiment, the case where the crank 402 and the lever 403 are used as the drive mechanism of the magnetic flux shielding plate 204 has been described. However, it goes without saying that the present invention is not limited to this, and instead of this, a wire Alternatively, the magnetic flux shielding plate 204 may be rotationally driven using another drive mechanism such as a drive mechanism using a link.

  Regardless of the drive mechanism. According to the present invention, since the magnetic flux shielding plate 204 is merely rotated without sliding the magnetic flux shielding plate 204 in the direction of the rotation axis of the fixing roller 141, the fixing device is increased in size to prevent overheating of the non-sheet passing portion. Can be prevented.

  (3) In the above-described embodiment, the case where ten, a total of 20 ferrite plates having a trapezoidal shape in plan view are used as one end of the fixing roller 141 as the magnetic flux shielding plate 204 has been described. However, the present invention is not limited to this. Needless to say, other shape members may be used.

  Further, a material other than ferrite may be used as long as it has a high magnetic permeability and a large specific resistance. Further, the number of magnetic flux shielding plates may be other than ten. In either case, the effects of the present invention can be obtained.

  (4) In the above embodiment, the case where the size of the large size paper is set to A4 horizontal has been described, but it is needless to say that the present invention is not limited to this. You may make it large and conversely may make it small. In any case, it is desirable that the size of the large size paper is determined by the length of the fixing roller 141 in the rotation axis direction.

  Similarly, the size of the small size paper is not limited to A4 vertical, and may be larger than A4 vertical, or conversely, may be smaller than A4 vertical such as postcard size. However, the length of the magnetic flux shielding plate 204 should be determined according to the size of the small size paper. The effect of the present invention can be obtained regardless of the size of large-size paper or small-size paper.

  (5) In the above embodiment, the case where the sheet passes through the center of the fixing roller 141 in the rotational axis direction has been described. However, the present invention is not limited to this, and one side of the fixing roller 141 The sheet may be passed on the basis of.

  When the sheet is passed on one side, it is only necessary to provide the magnetic flux shielding plate 204 only on the side opposite to the sheet passing reference side of the fixing roller 141, so that further space saving can be achieved and the number of parts can be reduced. This can reduce material costs, reduce assembly work, and shorten the construction period.

  (6) Although not particularly mentioned in the above embodiment, in this specification, an image forming apparatus is a printer, a copier, a facsimile machine, a multifunction machine having these functions, etc. A fixing device is provided, which fixes a toner image on a recording sheet.

  The heat fixing device and the image forming apparatus according to the present invention are useful as a technique for achieving both the elimination of problems caused by overheating of the fixing member in the IH type fixing device and the miniaturization of the fixing device.

1 is a diagram illustrating a main configuration of an image forming apparatus according to an embodiment of the present invention. 2 is a diagram illustrating a main configuration of a fixing device 140. FIG. It is a figure which shows the shape of the magnetic flux shielding board. FIGS. 4A and 4B are diagrams showing a driving mechanism of a magnetic flux shielding plate 204, where FIG. 5A shows the posture when passing large-size paper, and FIG. 5B shows the posture when passing small-size paper. 5 is a diagram illustrating a positional relationship between a large-size paper passing position and a magnetic flux shielding plate 204. FIG. FIG. 6 is a diagram illustrating a state of the fixing device 140 when a small-size sheet is passed. 6 is a diagram illustrating a positional relationship between a small-size paper passing position and a magnetic flux shielding plate 204. FIG. 6 is a diagram illustrating a positional relationship between a sheet passing position of medium size paper and a magnetic flux shielding plate 204. FIG. 2 is a diagram illustrating a configuration of a control unit 110. FIG. 3 is a flowchart showing an operation of a control unit 110. 6 is a flowchart showing attitude control of a magnetic flux shielding plate based on a fixing roller temperature. It is a flowchart which shows the attitude | position control of the magnetic flux shielding board based on a continuous sheet passing number.

Explanation of symbols

1 …………………… Image forming apparatus 140 …………………… Fixing unit 141 …………………… Fixing roller 142 ………………… Pressure roller 201 …………… …… Excitation coil 202 ……………… Ferrite core 203 ……………… Bottom core 204 ……………… Magnetic flux shielding plate 205 ……………… Non-contact thermistors 141 a and 142 a. Core bar 141b ……………… Silicone sponge layer 141c ……………… Heat belt 142b ……………… Heat-resistant elastic layer 142c ……………… Heat-resistant release layer 301 …………………… Pin 302 ……………… Rotating support shaft 401 ……………… Drive motor 402 ……………… Drive crank 403 …………………… Lever 402a ……………… Pin 403a , 403b ... Guide groove 501, ... ............ small size paper 801 ..................... in size paper

Claims (6)

A heating and fixing device that heats and fixes a toner image on a recording sheet that is passed over a fixing member that is electromagnetically heated by an exciting coil,
In the gap between the exciting coil and the fixing member, there are a plurality of narrow and long magnetic plates on the part that can be either the paper passing range or the non-passing range depending on the size of the recording sheet. A heat-fixing device, wherein the heat-fixing device is arranged so as to be freely rotatable in a state of being directed in a direction perpendicular to the horizontal axis, and to be spaced apart from each other during rotation. Rotation drive means for rotating the magnetic plate;
Control means for controlling the rotation driving means so that the interval between adjacent magnetic plates increases as the size of the recording sheet passing through increases, and the interval between the magnetic plates decreases as the size of the recording sheet passing through decreases. The heat fixing apparatus according to claim 1, comprising: The magnetic plate has a smaller width as it approaches the other end from one end in the longitudinal direction,
The heat fixing apparatus according to claim 1, wherein an end portion having a smaller width is disposed so as to face a center of the fixing member. A sensor for measuring the temperature of the fixing member;
The control means is configured such that the gap between the magnetic plates increases as the temperature of the fixing member decreases, and the gap between the magnetic plates increases as the temperature of the fixing member increases, even if the size of the recording sheet to be passed is the same. The heat fixing device according to claim 1, wherein the rotation driving unit is controlled to be small. It has a counter that counts the number of continuous paper passes,
The heat fixing apparatus according to claim 1, wherein the control unit controls the rotation driving unit so as to rotate the magnetic plate according to the number of continuous sheets. An image forming apparatus comprising the heat fixing device according to claim 1.

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