JP2012203220A - Fixing unit and image forming apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing unit that suitably performs a fixing process of a toner image, and an image forming apparatus.SOLUTION: A tension roller 540 is urged in an urging direction that extends along a stretch direction of a belt 511 laid between a heating roller 513 and the tension roller 540, and moves in the stretch direction of the belt 511 in accordance with the tensile force of the belt 511. A bearing 321 that rotatably supports a journal 320 of the tension roller 540 is slidably supported by a slit 322 of a support plate 554.

Description

  The present invention relates to a fixing unit that fixes a toner image on a sheet and an image forming apparatus incorporating the fixing unit.

  Image forming apparatuses such as copying machines, facsimile machines, and printers typically include a fixing unit that fixes a toner image on a sheet. One type of fixing unit includes a heating roller and a pressure roller pressed against the heating roller. While the sheet carrying the toner image passes through the nip portion between the heating roller and the pressure roller, the toner image is fixed to the sheet.

  Another type of fixing unit includes a heated belt and a pressure roller pressed against the belt. While the sheet passes through the nip between the belt and the pressure roller, the toner image is fixed to the sheet. Patent Document 1 discloses such a belt-type fixing unit.

  According to Patent Document 1, in addition to the above-described belt and pressure roller, the fixing unit includes a heating roller wound around the belt and a fixing roller that sandwiches the belt in cooperation with the pressure roller. The belt is wound around a heating roller and a fixing roller. The fixing unit includes a tension roller for maintaining the tension of the belt. The tension roller stabilizes the running of the belt.

  According to Patent Document 1, the fixing unit includes a heating mechanism that induction-heats the belt and the heating roller. The tension roller is biased in a direction orthogonal to the belt travel path defined between the heating roller and the fixing roller.

JP 2009-139664 A

  A tension roller urged in a direction perpendicular to the belt travel path defined between the heating roller and the fixing roller changes the distance between the heating mechanism and the belt. For example, when the belt tension decreases, the tension roller is displaced in a direction away from a straight line connecting the rotation center axis of the heating roller and the rotation center axis of the fixing roller. When the belt tension increases, the tension roller is displaced toward a straight line connecting the rotation center axis of the heating roller and the rotation center axis of the fixing roller.

  The separation of the tension roller with respect to the straight line connecting the rotation center axis of the heating roller and the rotation center axis of the fixing roller causes a variation in the distance between the belt and the heating mechanism at the start point and / or end point of the heating section defined by the heating mechanism. Let Variation in the distance between the belt and the heating mechanism, which is a disturbance factor for the temperature control of the belt, ultimately causes a problem in the toner image fixing process.

  The above-described problems are common not only to the induction heating type fixing unit but also to a fixing unit having another heating mechanism for supplying heat energy toward the outer surface of the belt.

  It is an object of the present invention to provide a fixing unit and an image forming apparatus that suitably perform a toner image fixing step.

  In order to achieve the above object, a fixing unit of the present invention includes a heating mechanism that defines an arc-shaped heating section, a heating roller that includes a peripheral surface along the heating section, and a winding around the heating roller along the peripheral surface. And a biasing element that biases the tensioning element in a biasing direction along a tensioning direction of the belt between the heating roller and the tensioning element. A mechanism, and a support element that supports the tension applying element, and the tension applying element includes a body that contacts the belt, a journal that extends from the body, and a bearing that rotatably supports the journal. A tension roller that is urged by the urging mechanism and includes a holder that houses the bearing, and the support element has a slit extending in the urging direction. Includes a lifting plate, by an outer peripheral surface of the bearing contacts the inner edge of the slit, is characterized in that the bearing is slidably supported by the biasing direction.

  According to the said invention, the tension roller urged | biased in the urging | biasing direction along the tension | tensile_strength direction of the belt between a heating roller and a tension roller moves to the tension | tensile_strength direction of a belt according to the tension | tensile_strength of a belt. Accordingly, since the distance between the heating mechanism and the belt does not vary, the amount of heating with respect to the belt is hardly affected by variations in belt tension. In addition, since the bearing that rotatably supports the tension row is movably supported by the slit of the support plate, the backlash between the belt and the tension roller is reduced, and the distance between the heating mechanism and the belt is reduced. Stabilize. As described above, the fixing unit and the image forming apparatus incorporating the fixing unit according to the present invention can suitably perform the toner image fixing step.

1 is a diagram illustrating a schematic configuration of an image forming apparatus incorporating a fixing unit according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a fixing unit provided in the image forming apparatus shown in FIG. 1. FIG. 3 is a schematic perspective view of the fixing unit shown in FIG. 2. FIG. 3 is a diagram schematically showing an IH coil unit included in the fixing unit shown in FIG. 2. FIG. 5 is a schematic cross-sectional view of a center core of the IH coil unit shown in FIG. 4. FIG. 5 is a schematic block diagram of a drive mechanism for the center core shown in FIG. 4. It is a figure which illustrates schematically the temperature control by rotation of the center core shown by FIG. FIG. 3 is a schematic plan view of a belt unit provided in the fixing unit shown in FIG. 2.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that terms used in the following description, such as “up”, “down”, “left”, “right” and the like, are merely for the purpose of clarifying the explanation and do not limit the present invention. Not what you want.

<Image forming apparatus>
FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus including a fixing unit. An image forming apparatus 1 shown in FIG. 1 is a tandem type color printer. The principle of the present embodiment is that printing is performed by transferring a toner image onto the surface of a print medium based on image information input from a printer, a copier, a facsimile machine, a multifunction machine having these functions, or an external input. It may be applied to other devices.

  The image forming apparatus 1 includes a square box-shaped housing 2. A color image is formed on the sheet inside the housing 2. A sheet discharge unit 3 is provided on the upper surface of the housing 2. A sheet on which a color image is printed is discharged to the sheet discharge unit 3. The sheet may be, for example, a copy sheet, a postcard, an OHP sheet, tracing paper, or other print medium capable of forming a toner image.

  The housing 2 accommodates a sheet feeding cassette 5 for supplying sheets and an image forming unit 7. A stack tray 6 for manually feeding sheets is attached to the housing 2. The stack tray 6 is disposed on the right side surface portion of the housing 2. The image forming unit 7 disposed above the stack tray 6 forms an image on a sheet based on image data such as characters and pictures transmitted from the outside of the image forming apparatus 1.

  A first transport path 9 is formed on the left side of the housing 2 shown in FIG. The sheet fed from the paper feed cassette 5 is conveyed to the image forming unit 7 through the first conveyance path 9. The second transport path 10 is formed above the paper feed cassette 5. The sheet sent from the stack tray 6 moves from the left side to the right side of the housing 2 through the second conveyance path 10 and reaches the image forming unit 7. A fixing unit 500 that performs fixing processing on a sheet that has been subjected to image forming processing by the image forming section 7 and a sheet that has been subjected to fixing processing are conveyed to the sheet discharge section 3 at the upper left in the housing 2. Three conveyance paths 11 are provided.

  The paper feed cassette 5 is formed so that it can be pulled out of the housing 2 (for example, on the right side in FIG. 1). The user can pull out the paper feed cassette 5 and replenish sheets. The paper feed cassette 5 includes a storage unit 16. The user can selectively store sheets of various sizes in the storage unit 16. The sheets stored in the storage unit 16 are fed out one by one toward the first conveyance path 9 by the paper feed roller 17 and the pair of rolling rollers 18.

  The stack tray 6 can be rotated up and down between a closed position along the outer surface of the housing 2 and an open position (shown in FIG. 1) protruding from the outer surface of the housing 2. Sheets are placed one by one on the manual feed portion 19 of the stack tray 6. Alternatively, the user may place a plurality of sheets on the manual feed portion 19. The sheets placed on the manual feed unit 19 are fed out one by one by the pickup roller 20 and the pair of rolling rollers 21 toward the second conveyance path 10.

  The first transport path 9 and the second transport path 10 merge before the registration roller pair 22. The sheet that has reached the registration roller pair 22 is temporarily stopped by the registration roller pair 22. Thereafter, the registration roller pair 22 performs skew adjustment and timing adjustment on the sheet. After the skew adjustment and the timing adjustment, the registration roller pair 22 sends the sheet toward the secondary transfer unit 23. The full color toner image on the intermediate transfer belt 40 is secondarily transferred to the sheet sent to the secondary transfer unit 23. After the secondary transfer, the sheet is sent to the fixing unit 500. The fixing unit 500 fixes the toner image on the sheet. If necessary, after the toner image is fixed on one side of the sheet, a new full-color toner image may be formed on the other side of the sheet in the secondary transfer unit 23 (double-sided printing). . When double-sided printing is performed, after the toner image is fixed on one side of the sheet, the sheet is sent to the fourth conveyance path 12 and reversed. The new toner image formed on the other surface by the secondary transfer unit 23 is fixed by the fixing unit 500. Thereafter, the sheet passes through the third conveyance path 11 and is discharged to the sheet discharge unit 3 by the discharge roller pair 24.

  The image forming unit 7 includes four image forming units 26 to 29 that respectively form black (Bk), yellow (Y), cyan (C), and magenta (M) toner images, and a laser scanning unit 34. The image forming unit 7 further includes an intermediate transfer unit 30. The intermediate transfer unit 30 combines and holds the toner images formed by these image forming units 26 to 29. The laser scanning unit 34 emits a laser beam to the peripheral surface of the photosensitive drum 32 of each of the image forming units 26 to 29 in accordance with image data such as characters and pictures transmitted from the outside of the image forming apparatus 1.

  Each of the image forming units 26 to 29 includes a photosensitive drum 32 and a charging unit 33 disposed to face the peripheral surface of the photosensitive drum 32. The laser beam from the laser scanning unit 34 is applied to the peripheral surface of the photosensitive drum 32 on the downstream side in the rotation direction of the photosensitive drum 32 when viewed from the charging unit 33. Each of the image forming units 26 to 29 further includes a developing unit 35 that is disposed to face the peripheral surface of the photosensitive drum 32 on the downstream side in the rotation direction of the photosensitive drum 32 when viewed from the irradiation position of the laser beam. The developing unit 35 supplies toner to the peripheral surface of the photosensitive drum 32 that carries the electrostatic latent image formed by the laser beam irradiation, and forms a toner image. The toner image formed on the peripheral surface of the photosensitive drum 32 is transferred to the intermediate transfer unit 30 (primary transfer). Each of the image forming units 26 to 29 further includes a cleaning unit 36 disposed to face the peripheral surface of the photosensitive drum 32 on the downstream side in the rotation direction of the photosensitive drum 32 when viewed from the developing unit 35. The cleaning unit 36 cleans the peripheral surface of the photosensitive drum 32 after the primary transfer.

  The photosensitive drums 32 of the image forming units 26 to 29 shown in FIG. 1 are rotated counterclockwise by a drive motor (not shown). In each developing device 51 of the developing unit 35 of each of the image forming units 26 to 29, two-component developers each containing black toner, yellow toner, cyan toner, and magenta toner are stored.

  The intermediate transfer unit 30 includes a rear roller (drive roller) 38 disposed in the vicinity of the image forming unit 26, a front roller (driven roller) 39 disposed in the vicinity of the image forming unit 29, and a rear roller. And an intermediate transfer belt 40 extending between the front roller 39 and the front roller 39. The intermediate transfer unit 30 further includes four transfer rollers 41 that press the intermediate transfer belt 40 against the photosensitive drums 32 of the image forming units 26 to 29. The transfer roller 41 presses the intermediate transfer belt 40 against the peripheral surface of the photosensitive drum 32 carrying the toner image formed by the developing unit 35, thereby achieving transfer (primary transfer) of the toner image to the intermediate transfer belt 40.

  As a result of the transfer of the toner image to the intermediate transfer belt 40, the toner images formed by the black toner, yellow toner, cyan toner and magenta toner are superimposed on the intermediate transfer belt 40 to form a full-color toner image. .

  The first transport path 9 extends toward the intermediate transfer unit 30. The sheet sent from the paper feed cassette 5 reaches the intermediate transfer unit 30 through the first conveyance path 9. A plurality of conveyance roller pairs 43 for conveying the sheet are arranged at appropriate positions along the first conveyance path 9. The registration roller 22 disposed upstream of the intermediate transfer unit 30 adjusts the sheet feeding timing of the sheet passing through the first conveyance path 9 in accordance with the image forming operation of the image forming unit 7.

  The fixing unit 500 heats and pressurizes the sheet. As a result, the unfixed toner image formed immediately after the secondary transfer formed on the sheet is fixed on the sheet. The fixing unit 500 includes a belt unit 510 including a belt 511 that is pressed against the sheet, and a reference roller 520 that cooperates with the belt 511 to sandwich the sheet. The belt unit 510 includes a first roller 512 and a second roller 513 that are wound around the belt 511. In this embodiment, the 2nd roller 513 is illustrated as a heating roller containing the surrounding surface in alignment with the heating area prescribed | regulated by the heating mechanism mentioned later.

  A conveyance roller pair 49 is disposed downstream of the fixing unit 500. A conveyance path 47 extending from the secondary transfer portion 23 toward the conveyance roller pair 49 is formed in the housing 2. The sheet conveyed through the intermediate transfer unit 30 is introduced through a conveyance path 47 into a nip portion formed between the reference roller 520 and the belt 511. The toner image is fixed on the sheet at the nip portion. The sheet that has passed between the reference roller 520 and the belt 511 is then guided to the third conveyance path 11 through the conveyance path 47.

  The conveyance roller 49 sends out the sheet to the third conveyance path 11. The third conveyance path 11 guides the sheet that has been subjected to the fixing process by the fixing unit 500 to the sheet discharge unit 3. Further, the discharge roller pair 24 disposed at the exit of the third conveyance path 11 discharges the sheet to the sheet discharge unit 3.

<Fusing unit>
FIG. 2 is a schematic cross-sectional view of the fixing unit 500. FIG. 3 is a schematic perspective view of the fixing unit 500. The fixing unit 500 will be described with reference to FIGS. 1 to 3.

(Heating mechanism)
The fixing unit 500 includes an IH coil unit 530 that heats the belt 511 and the second roller 513 in addition to the belt unit 510 and the reference roller 520 described above. In the present embodiment, the IH coil unit 530 is exemplified as a heating mechanism.

  The IH coil unit 530 disposed adjacent to the second roller 513 includes a platform 200 having a substantially Ω-shaped cross section (see FIG. 2). In FIG. 3, the platform 200 is not shown. The platform 200 molded into a thin plate shape from a non-conductive heat resistant resin (for example, PPS, PET, LCP) includes a curved surface portion 230 having a substantially semi-cylindrical shape in cross-sectional view. The curved surface portion 230 includes a pair of end edges that are substantially parallel to the rotation center axis of the second roller 513. The platform 200 further includes a pair of tabular ears 240 extending from each of the pair of edges of the curved surface portion 230. Each of the pair of ears 240 is fixed to the housing 2 of the image forming apparatus 1 using an appropriate fixing tool 250 (for example, a bolt).

  The curved surface portion 230 includes a pair of positioning walls 231 that protrude in a direction away from the second roller 513. The positioning wall 231 extends substantially parallel to the rotation center axis of the second roller 513. The IH coil unit 530 includes a coil 531 that is fixed to the curved surface portion 230. A coil 531 including an enameled wire wound with reference to the pair of positioning walls 231 forms a coil surface 532 along the curved surface portion 230.

  The IH coil unit 530 includes a power source (not shown) that supplies power to the coil 531. The coil 531 generates a magnetic field by supplying power from the power source.

  The IH coil unit 530 includes a magnetic element 260 that defines a path of magnetic lines of force in the magnetic field generated from the coil 531. The magnetic element 260 includes a pair of flat side cores 533 fixed to the pair of ears 240. The side core 533 is molded from ferrite, for example. A path of magnetic lines of force in the magnetic field generated from the coil 531 passes through the side core 533. Thus, the pair of side cores 533 defines the start point S and the end point E of the heating section that is induction-heated by the magnetic field from the coil 531. The IH coil unit 530 induction-heats the belt 511 and the second roller 513 wound along the peripheral surface of the second roller 513 in an arc-shaped heating section from the start point S to the end point E (see FIG. 2).

  The magnetic element 260 further includes a center core 535 disposed at an intermediate position of the heating section, and an arch core 534 extending between each of the pair of side cores 533 and the center core 535. The arch core 534 is molded from ferrite, for example. The center core 535 is disposed substantially parallel to the second roller 513. A part of the center core 535 is surrounded by the inner edge of the coil surface 532. A proximal end portion of the arch core 534 is connected to the side core 533. The other end of the arch core 534 is close to the peripheral surface of the center core 535. The coil surface 532 is disposed in a region surrounded by the center core 535, the arch core 534, the side core 533, and the belt 511 existing in the heating section.

  FIG. 4 schematically shows the coil 531, the side core 533, the arch core 534, and the center core 535 mounted on the platform 200. The IH coil unit 530 is further described with reference to FIGS.

  The arch core 534 includes, for example, arch core pieces 537 arranged at a plurality of positions at intervals in the longitudinal direction of the center core 535. The arch core piece 537 may be a ferrite member having a substantially L shape with a width of about 10 mm, for example. The high arrangement density of the arch core pieces 537 improves the heating efficiency. On the other hand, the reduction in the arrangement density of the arch core pieces 537 contributes to a reduction in manufacturing cost and a reduction in the weight of the fixing unit 500. Therefore, the arrangement density of the arch core pieces 537 is preferably determined appropriately based on heating efficiency, manufacturing cost, and / or weight reduction. In the present embodiment, the plurality of arch core pieces 537 are aligned at an equal pitch. Alternatively, the arrangement density of the arch core pieces 537 may be reduced near the center position in the longitudinal direction of the center core 535, and the arrangement density of the arch core pieces 537 may be increased near the end of the center core 535. The gap between the arch core pieces 537 may be determined, for example, in the range of 1/3 or more and 1/2 or less of the width of the arch core pieces 537.

  The side core 533 may be formed of, for example, a plurality of ferrite plates that are 30 mm or more and 60 mm or less arranged continuously. The arrangement of the arch core 534 and the side core 533 may be determined according to the magnetic flux density (magnetic field strength) distribution of the magnetic field generated from the coil 531, for example. In the portion where the arch core piece 537 does not exist, the side core 533 compensates for the magnetic field focusing effect, and makes the magnetic flux density distribution (temperature difference) in the longitudinal direction of the center core 535 uniform.

  FIG. 5 is a cross-sectional view of the center core 535 in the longitudinal direction. The IH coil unit 530 is further described with reference to FIGS. 2, 3, and 5.

  The center core 535 includes a columnar conductive shaft 538 and a cylindrical magnetic tube 539 that covers the conductive shaft 538. The magnetic cylinder 539 is bonded to the conductive shaft 538 using, for example, a silicon-based adhesive. The magnetic cylinder 539 has a cylindrical shape with an outer diameter of 14 mm or more and 20 mm or less, for example. The conductive shaft 538 includes a body portion 541 that fits into a cylindrical magnetic tube 539 and a pair of journals 542 and 543. The journals 542 and 543 are formed narrower than the body portion 541. Journals 542 and 543 formed coaxially with the body portion 541 protrude outward from the magnetic cylinder 539. The conductive shaft 538 is preferably formed from non-magnetic stainless steel. The stainless steel conductive shaft 538 suppresses deformation of the center core 535. The journals 542 and 543 are preferably coated using a non-conductive member. Thus, current transmission from the coil 531 to the conductive shaft 538 is suppressed.

  The magnetic cylinder 539 includes a plurality of magnetic cylinder pieces 544 having a substantially cylindrical shape. The magnetic cylinder piece 544 is molded from ferrite, for example. The plurality of magnetic cylinder pieces 544 are continuously provided along the conductive shaft 538. The outer diameter of the magnetic cylinder piece 544 arranged at the longitudinal center position of the conductive shaft 538 is larger than the outer diameter of the magnetic cylinder piece 544 positioned at the left and right ends of the body portion 541 of the conductive shaft 538. The outer peripheral surface of the magnetic cylinder piece 544 having a small diameter so that the magnetic shielding plate 545 compensates for the step between the magnetic cylinder piece 544 located at the center of the conductive shaft 538 and the magnetic cylinder piece 544 located at the left and right ends of the conductive shaft 538. Is partially covered. In the present embodiment, the peripheral surface region of the center core 535 to which the magnetic shielding plate 545 is attached is exemplified as a blocking region that blocks a path of magnetic lines of force toward the second roller 513.

  The magnetic shielding plate 545 is preferably formed from a nonmagnetic and highly conductive material (for example, oxygen-free copper). The penetration of the magnetic field perpendicular to the surface of the magnetic shielding plate 545 generates an induced current. This induced current generates a reverse magnetic field and cancels the interlaced magnetic flux (perpendicular through magnetic field). As a result, the magnetic shielding plate 545 can shield the magnetic field. The magnetic shielding plate 545 formed of a highly conductive member can further suppress Joule heat generation due to the induced current and efficiently shield the magnetic field. The magnetic shielding plate 545 and / or the thick magnetic shielding plate 545 formed of a material having a small specific resistance has high conductivity. The plate thickness of the magnetic shielding plate 545 is preferably 0.5 mm or more. In the present embodiment, a magnetic shielding plate 545 having a thickness of about 1 mm is used.

  FIG. 6 is a schematic diagram showing the configuration of the drive mechanism connected to the center core 535. A drive mechanism for rotating the center core 535 will be described with reference to FIGS. 1, 5, and 6.

  The drive mechanism 64 rotates the center core 535 through the journal 542 (or the journal 543). The position of the magnetic shielding plate 545 is changed by the rotation of the center core 535. With the movement of the magnetic shielding plate 545, it is possible to select whether to shield (suppress) the magnetic lines of force in the magnetic field generated by the power supply to the coil 531.

  The drive mechanism 64 includes, for example, a stepping motor 66 and a speed reducer 68 that decelerates the rotation of the stepping motor 66. A gear 549 connected to the journal 542 of the center core 535 meshes with the speed reducer 68. The stepping motor 66 rotates the center core 535 via the speed reducer 68 and the gear 549. As the speed reducer 68, for example, a worm gear may be used. The drive mechanism 64 further includes a slit-equipped disk 72 that rotates in conjunction with the rotation of the gear 549 and a rotation angle of the slit-equipped disk 72 (that is, a rotation angle of the center core 535 (a rotational displacement amount from the reference position)). And a photo interrupter 74 for detection.

  The rotation angle of the center core 535 is controlled by the number of drive pulses applied to the stepping motor 66, for example. The drive mechanism 64 includes a control circuit 640 that controls the rotation of the stepping motor 66. The control circuit 640 includes, for example, a control IC 641, an input driver 642, an output driver 643, and a semiconductor memory 644. A detection signal from the photo interrupter 74 is input to the control IC 641 through the input driver 642. Based on the input signal, the control IC 641 detects the current rotation angle (position) of the center core 535. On the other hand, an information signal regarding the current sheet size is transmitted to the control IC 641 from the image formation control unit 650 included in the image forming apparatus 1. After receiving the information signal from the image formation control unit 650, the control IC 641 reads out information on the rotation angle suitable for the sheet size from the semiconductor memory (ROM) 644, and drives pulses for reaching the target rotation angle. Is output at regular intervals. The drive pulse is applied to the stepping motor 66 through the output driver 643. The stepping motor 66 operates according to the driving pulse. If only the reference position needs to be detected when controlling the stepping motor 66, the slit disk 72 may be used as the index member. The index member may be detected by the photo interrupter 74 at the reference position.

(Belt unit and reference roller)
The belt unit 510 and the reference roller 520 will be described with reference to FIGS. 2 and 3 again.

  The belt unit 510 includes a first roller 512, a second roller 513 disposed between the IH coil unit 530 and the first roller 512, and a belt 511 that winds the first roller 512 and the second roller 513. including. The reference roller 520 sandwiches the belt 511 in cooperation with the first roller 512. A flat nip is formed between the reference roller 520 and the belt 511.

  The belt 511 includes, for example, a nickel electroformed base material having a thickness dimension of about 30 μm or more and about 50 μm or less, a silicon rubber layer laminated on the nickel electroformed base material, and a release layer formed on the silicon rubber layer ( For example, a PFA layer). The second roller 513 is formed in a cylindrical shape with an outer diameter of 30 mm, for example. The second roller 513 includes a cylindrical iron base and a release layer (for example, a PFA layer) having a thickness of 0.2 mm to 1.0 mm formed on the outer peripheral surface of the iron base. The first roller 512 is formed in a columnar shape, for example. The first roller 512 includes a core metal roller having an outer diameter of 45 mm made of stainless steel and a sponge layer made of silicon rubber having a thickness of 5 mm to 10 mm that covers the outer peripheral surface of the core metal roller. The reference roller 520 is formed in a cylindrical shape with an outer diameter of 50 mm, for example. The reference roller 520 includes a core metal roller made of stainless steel, a sponge layer made of silicon rubber having a thickness of 2 mm to 5 mm and covering a peripheral surface of the core metal roller, and a release layer (for example, a PFA layer). The metal core material of the reference roller 520 may be formed using, for example, Fe or Al. A Si rubber layer may be formed on the core material. Further, a fluororesin layer may be formed on the surface layer of the Si rubber layer.

  The fixing unit 500 further includes a tension roller 540 that applies tension to the belt 511. The tension roller 540 includes a body part 310 that abuts on the inner surface of the belt 511 from the second roller 513 toward the first roller 512, and a journal 320 that extends from the end part of the body part 310 (see FIG. 3). The tension roller 540 contributes to suppression of bending of the belt 511 during traveling and stabilization of traveling of the belt 511. The body portion 310 is preferably made of aluminum. Due to the high thermal conductivity of the body 310 made of aluminum, fluctuations in the temperature distribution of the belt 511 are reduced.

  The fixing unit 500 includes a temperature sensor 62 that measures the temperature of the belt 511 in a non-contact manner. The temperature sensor 62 attached to the platform 200 is preferably disposed to face a portion where the amount of heat generated by induction heating is the largest. Note that the temperature of the belt 511 may be measured using a thermostat instead of the temperature sensor. Alternatively, the temperature sensor 62 or the thermostat may be disposed inside the second roller 513. The arrangement of temperature measuring elements such as temperature sensors and thermostats contributes to improving safety when abnormal temperatures rise.

(Heat amount control for belt unit)
FIG. 7 schematically illustrates heat amount control for the belt unit 510. FIG. 7A is a cross-sectional view schematically showing the fixing unit 500 including the magnetic shielding plate 545 disposed at the retreat position farthest from the second roller 513. FIG. 7B is a cross-sectional view schematically showing the fixing unit 500 including the magnetic shielding plate 545 disposed at the closest position closest to the second roller 513. The heat amount control for the belt unit 510 will be described with reference to FIGS. 6 and 7.

  The rotation of the center core 535 by the drive mechanism 64 is used for heat amount control on the belt unit 510. The fixing process for a large-sized sheet requires a heat amount supply in a relatively wide range. On the other hand, the fixing process for a small-sized sheet requires a heat amount supply in a relatively narrow range. When a large sized sheet passes through the fixing unit 500, the drive mechanism 64 rotates the center core 535 so that the magnetic shielding plate 545 reaches the retracted position. When a small-sized sheet passes through the fixing unit 500, the driving mechanism 64 rotates the center core 535 so that the magnetic shielding plate 545 reaches the close position.

  When the magnetic shielding plate 545 is in the retracted position, the magnetic field lines of the magnetic field generated by the coil 531 pass through the second roller 513 and the belt 511 via the first path P1 passing through the side core 533, the arch core 534, and the center core 535. pass. As a result, eddy currents are generated in the ferromagnetic belt 511 and the second roller 513. Eddy currents generate Joule heat according to the specific resistance of each material. Thus, the belt 511 and the second roller 513 are entirely heated without being obstructed by the magnetic shielding plate 545.

  When fixing a small-size sheet, the path of the lines of magnetic force in the magnetic field generated by the coil 531 is switched by the rotation of the center core 535. The magnetic shielding plate 545 located at the close position exists between the center core 535 and the second roller 513. Accordingly, the first magnetic force path P1 shown in FIG. 7A is blocked by the magnetic shielding plate 545, so that the strength of the lines of magnetic force is significantly reduced. As a result, in the fixing process for a small size sheet, the amount of heat generated by the belt 511 and the second roller 513 opposed to both ends of the center core 535 provided with the magnetic shielding plate 545 is reduced.

(Belt unit)
FIG. 8 is a plan view of the belt unit 510. The belt unit 510 is described with reference to FIGS. 2, 3, and 8.

  The second roller 513 of the belt unit 510 includes a substantially cylindrical body 518 (see FIG. 3) that forms a travel path of the belt 511 along the arc-shaped heating section, and a journal 552 that protrudes from an end surface of the body 518 (see FIG. 3). 3), a bearing 561 (see FIG. 3) for connecting the body 518 and the journal 552, and a pair of disc-shaped flanges 519 (see FIG. 3) along both edges of the belt 511. A flange 519 having a diameter larger than that of the body 518 defines the maximum runout width of the belt 511. The lateral position of the belt 511 is properly accommodated between the pair of flanges 519 by the flange 519. The body portion 518 rotates around the journal 552 via the bearing 561. A driving force for rotating the body 518 is transmitted from the first roller 512 via the belt 511.

  A bracket 562 (see FIG. 3) is attached to the journal 552 of the second roller 513. The bracket 562 is used for connection to a support frame (not shown) that supports the belt unit 510 and the reference roller 520.

  As shown in FIG. 8, the belt unit 510 includes a support plate 554. The second roller 513 is appropriately supported by the support plate 554. The tension roller 540 includes a bearing 321 that rotatably supports the journal 320. The bearing 321 includes a sliding bearing or a rolling bearing in which a ball is interposed on the journal 320. The support plate 554 is formed with a slit 322 for receiving the bearing 321. A support edge 323 that defines the contour of the slit 322 supports the bearing 321 in a movable manner. Thus, in the present embodiment, the support plate 554 is exemplified as a support element that supports the tension roller 540.

  The slit 322 formed in the support plate 554 extends in a first direction F substantially parallel to a travel section (see FIG. 2) of the belt 511 defined by the second roller 513 and the tension roller 540. In the travel section defined by the second roller 513 and the tension roller 540, the belt 511 substantially coincides with a common tangent line between the body 518 of the second roller 513 and the body 310 of the tension roller 540. The slit 322 allows the displacement of the tension roller 540 along the first direction F.

  As shown in FIG. 2, the tension roller 540 bends the belt 511 outward from the common tangent line T between the first roller 512 and the second roller 513. Accordingly, the tension of the belt 511 is appropriately maintained by the component force of the force that displaces the tension roller 540 along the first direction F (the force component orthogonal to the common tangent line T). Thus, the tension roller 540 appropriately removes the slack of the belt 511.

  As shown in FIG. 8, the bearing 321 is accommodated in the holder 326. The substantially rectangular holder 326 extends along the support edge 323 of the slit 322. A coil spring 340 is engaged with the peripheral edge of the holder 326 and the protruding piece 324 of the slit 322. The coil spring 340 is a compression spring that extends substantially parallel to the first direction F between the peripheral edge of the holder 326 and the protruding piece 324 of the slit 322. Therefore, the coil spring 340 biases the holder 326 toward the first direction F.

  A pair of openings 327 are formed in the center of the holder 326. Part of the outer peripheral surface of the bearing 321 is exposed from the pair of openings 327. The outer peripheral surface of the bearing 321 is movably supported by the support edge 323 of the slit 322.

  The coil spring 340 urges the tension roller 540 together with the holder 326 in the first direction F. The bearing 321 attached to the journal 320 of the tension roller 540 is guided by the slit 322 formed in the support plate 554 and moves along the first direction F. Thus, the tension roller 540 urged in the urging direction along the belt tensioning direction between the second roller 513 and the tension roller 540 moves in the first direction F according to the tension of the belt 511. Since the distance between the side core 544 and the belt 511 at the end point E (see FIG. 2) of the heating section does not fluctuate, the amount of heat applied to the belt 511 is hardly affected by the fluctuation in the tension of the belt 511.

  Since the outer peripheral surface of the bearing 321 is movably supported by the support edge 323 of the slit 322, rattling between the belt 511 and the tension roller 540 is reduced, and the distance between the side core 544 and the belt 511 is stable. To do.

  The present invention is applicable to various image forming apparatuses such as a color printer, a printer, a copying machine, a facsimile machine, and a multifunction machine having these functions.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 64 ... Drive mechanism 260 ... Magnetic element 310 ... Body part 320 ... Journal (Tension addition element)
321 ... Bearing (tensioning element)
322 ... Slit (supporting element)
326 ... Holder (Tension applying element)
340 ... Coil spring (biasing mechanism)
500... Fixing unit 511... Belt 513... Second roller (heating roller)
530 ... IH coil unit (heating mechanism)
531 ... Coil 532 ... Coil surface 533 ... Side core 534 ... Arch core 535 ... Center core 540 ... Tension roller (tension applying element)
554 ... Support plate (support element)
E: End point F: 1st direction (biasing direction)
S: Starting point

Claims (2)

A heating mechanism that defines an arcuate heating section;
A heating roller including a peripheral surface along the heating section;
A belt wound around the heating roller along the peripheral surface;
A tensioning element that applies tension to the belt;
A biasing mechanism that biases the tension applying element in a biasing direction along a tensioning direction of the belt between the heating roller and the tension applying element;
A support element for supporting the tension applying element,
The tension applying element includes a body that abuts on the belt, a journal extending from the body, a bearing that rotatably supports the journal, and a holder that is urged by the urging mechanism and stores the bearing. Including a tension roller comprising
The support element includes a support plate in which a slit extending in the biasing direction is formed, and the bearing is slidable in the biasing direction when an outer peripheral surface of the bearing is in contact with an inner edge of the slit. The fixing unit is supported by the fixing unit.   An image forming apparatus comprising the fixing unit according to claim 1.

Images