JP2018159809A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible, when a plurality of pressure member requiring adjustment of an applied pressure are present, to press the plurality of pressure members with different applied pressures with a single pressing mechanism.SOLUTION: A fixing device comprises: a heating belt 51 that has a heat source; a pressure belt 52 and a pressure roller 53 that are in pressure contact with the heating belt 51 at different positions; a first support lever 61 that supports the pressure belt 52; a second support lever 62 that supports the pressure roller 53; a first coil spring 66 that urges the pressure belt 52 to be in pressure contact with the heating belt 51; a second coil spring 67 that urges the pressure roller 53 to be in pressure contact with the heating belt 51; and a third support lever 63 that is arranged to urge the first support lever 61 with the first coil spring 66 and urges the second support lever 62 with the second coil spring 67, and is arranged movably in a direction contacting/separating from the heating belt 51.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a fixing device and an image forming apparatus.

  Conventionally, as a fixing device, a heating member and a pressure member are pressed against each other, a recording medium holding an unfixed toner image is passed through a nip portion formed between the heating member and the pressure member, and heat and pressure are passed. In some cases, an unfixed toner image is fixed on a recording medium. As a technique that makes it possible to adjust the pressure applied to the heating member of the pressure member in such a fixing device, for example, those disclosed in Patent Documents 1 and 2 have already been proposed.

  Patent Document 1 discloses a pair of rollers facing each other, and a pressure member that presses one of the rollers toward the other roller and presses the recording medium at a fixing pressure contact portion formed between the pair of rollers. And a fixing device for fixing a toner image formed on the recording medium, wherein the pressing member includes a long pressing lever whose one end is supported by a supporting shaft, and the pressing lever. By energizing the other end side, an elongate energizing member that energizes the one roller toward the other roller at an operating point between the other end side and the support shaft, The urging member has one end fixed, and the pressure lever is engaged with the other end of the urging member, and the urging force of the urging member acts to act as a force point. And the locking portion is spaced apart from the support shaft, and the separated position. And a line segment connecting the support shaft and the separation position, and a line segment connecting the separation position and one end of the urging member. The angle formed by is configured to be 90 degrees or more.

  Patent Document 2 includes a heating member provided with a heating source therein and a pressure member pressed against the heating member, and the recording material passes through a nip portion between the heating member and the pressure member. In a fixing device that fixes a toner image on a recording material to the recording material, a holding member that holds the pressing member so as to be movable in a pressing direction and a separation direction to the heating member, and the pressing member is in pressure contact with the heating member. A biasing member that biases the holding member, and a pressure adjusting means that engages with the holding member and adjusts the pressure applied to the heating member by the pressure member. is there.

JP 2014-178467 A JP 2012-013876 A

  An object of the present invention is to enable a plurality of pressing members to be pressed with different pressing forces by a single pressing mechanism when there are a plurality of pressing members that require adjustment of the pressing force.

The invention described in claim 1 is a heating member that is heated and rotated by a heating source;
At least first and second pressure members rotating in pressure contact with the heating member at different positions;
A first support member that movably supports the first pressure member in a direction in which the first pressure member contacts and separates from the heating member;
A second support member that movably supports the second pressurizing member in a direction of coming into contact with and separating from the heating member;
A first urging member that urges the first pressure member to press against the heating member;
A second urging member that urges the second pressure member to press against the heating member;
The first support member is urged through the first urging member, and the second support member is urged through the second urging member, and is in contact with the heating member. A third support member that is movably disposed in a separating direction;
A fixing device.

  According to a second aspect of the present invention, the first to third support members are rotatably supported around the same fulcrum, and the first support member is biased by the first urging member from the fulcrum. The ratio of the distance from the fulcrum to the force point that receives the biased force and the distance from the fulcrum to the action point at which the first support member applies pressure to the heating member from the fulcrum The distance from the fulcrum to the force point at which the second support member receives the force urged by the second urging member, and the action that the second support member applies the second pressure member to the heating member from the fulcrum The fixing device according to claim 1, wherein the fixing device is set to be larger than a ratio to a distance to a point.

  According to a third aspect of the present invention, the first and second support members are force points at which the first and second support members receive a force urged by the first and second urging members from the fulcrum. 3. The fixing device according to claim 2, wherein a distance from the fulcrum is set to be longer than a distance from the fulcrum to a force point that receives a force for rotating the third support member in a direction approaching the heating member.

  According to a fourth aspect of the present invention, the first and second support members are rotatably supported around different fulcrums located on the first support member side, and the fulcrum of the first support member is The fixing device according to claim 1, wherein the fixing device is spaced apart from a fulcrum of the second support member on a side opposite to the second support member.

  The invention described in claim 5 is the fixing device according to claim 4, wherein the third support member is supported rotatably about the same fulcrum as the second support member.

  According to a sixth aspect of the present invention, the first and second urging members are arranged close to each other in a tangential direction centering on a fulcrum of the first and second support members. The fixing device according to any one of the above.

  The invention described in claim 7 is the fixing device according to any one of claims 1 to 6, wherein the first urging member includes a torsion spring disposed around the fulcrum.

The invention described in claim 8 is an image forming unit that forms an image on a recording medium;
Fixing means for fixing an image formed on the recording medium by the image forming unit;
With
An image forming apparatus using the fixing device according to claim 1 as the fixing unit.

  According to the first aspect of the present invention, when there are a plurality of pressing members that require adjustment of the pressing force, the pressing members can be pressed with different pressing forces by a single pressing mechanism. .

  According to the second aspect of the present invention, the first pressing member can be pressed against the heating member with a larger pressing force than the second pressing member.

  According to the invention described in claim 3, the adjustable width of the means for rotating the third support member can be increased.

  According to the fourth aspect of the present invention, the separation distance of the first pressure member from the heating member can be increased.

  According to the invention described in claim 5, the configuration can be simplified as compared with the case where the fulcrum of the third support member is different from that of the second support member.

  According to the invention described in claim 6, the urging force of the first and second urging members can be effectively transmitted to the first and second support members.

  According to the invention described in claim 7, the configuration can be simplified.

  According to the invention described in claim 8, when there are a plurality of pressurizing members that require adjustment of the pressurizing force, a plurality of pressurizing members can be pressed with different pressurizing forces by a single pressing mechanism. It is possible to improve the fixing performance while achieving downsizing of the fixing device.

1 is a schematic configuration diagram showing an image forming apparatus to which a fixing device according to Embodiment 1 of the present invention is applied. 1 is a configuration diagram illustrating an image forming unit of an image forming apparatus according to Embodiment 1 of the present invention; 1 is a cross-sectional configuration diagram illustrating a fixing device according to a first embodiment of the present invention. 1 is a cross-sectional configuration diagram illustrating a fixing device according to a first embodiment of the present invention. It is a perspective block diagram which shows a heating belt. It is a perspective block diagram which shows the edge part of a heating belt. 1 is a front configuration diagram illustrating a fixing device according to Embodiment 1 of the present invention; It is a front lineblock diagram showing the 1st support lever. It is a perspective lineblock diagram showing the 1st support lever. It is a perspective block diagram which shows a lever unit. It is a perspective block diagram which shows a 2nd support lever. It is a perspective block diagram which shows a 3rd support lever. It is a section lineblock diagram showing a lever unit. FIG. 3 is a cross-sectional configuration diagram illustrating a nip release state of the fixing device according to the first embodiment of the present invention. It is a cross-sectional block diagram which shows the fixing device based on Embodiment 2 of this invention. It is a cross-sectional block diagram which shows the principal part of the fixing device which concerns on Embodiment 3 of this invention. It is a perspective view showing a torsion spring. It is a perspective block diagram which shows the 1st support lever in the fixing device which concerns on Embodiment 3 of this invention. It is a perspective block diagram which shows the principal part of the fixing device which concerns on Embodiment 3 of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

[Embodiment 1]
1 and 2 show an image forming apparatus to which the fixing device according to the first embodiment is applied. FIG. 1 shows an outline of the whole image forming apparatus, and FIG.

<Overall Configuration of Image Forming Apparatus>
The image forming apparatus 1 according to the first embodiment is configured as a color printer, for example. The image forming apparatus 1 includes a plurality of image forming apparatuses 10 as an example of an image forming unit that forms a toner image developed with toner constituting the developer 4, and toner images formed by the image forming apparatuses 10. An intermediate transfer device 20 that respectively holds and finally transports it to a secondary transfer position for secondary transfer onto a recording sheet 5 as an example of a recording medium, and a required recording to be supplied to the secondary transfer position of the intermediate transfer device 20 A paper feeding device 30 that accommodates and conveys the paper 5 and a fixing device 50 that fixes the toner image on the recording paper 5 that has been secondarily transferred by the intermediate transfer device 20 are provided. In the figure, reference numeral 1a denotes an apparatus main body of the image forming apparatus 1. The apparatus main body 1a includes a support structure member made of a plate or the like, an exterior cover, and the like. A broken line in the figure indicates a main conveyance path through which the recording paper 5 is conveyed in the apparatus main body 1a.

  The image forming device 10 includes four image forming devices 10Y, 10M, 10C, and 10K that respectively form four color toner images exclusively for yellow (Y), magenta (M), cyan (C), and black (K). It is configured. These four image forming apparatuses 10 (Y, M, C, K) are arranged so as to be arranged in a line in an inclined state in the internal space of the apparatus main body 1a. The four image forming devices 10 (Y, M, C, and K) are relatively high because the yellow (Y) image forming device 10Y is positioned above the vertical direction, and the black (K) image forming device. 10K exists at a relatively low position.

  As shown in FIG. 1 and FIG. 2, the four image forming apparatuses 10 (Y, M, C, and K) include a rotating photosensitive drum 11 as an example of an image holding member. Each apparatus as an example of the following toner image forming unit is mainly disposed around the apparatus 11. The main devices are a charging device 12 that charges a peripheral surface (image holding surface) on the photosensitive drum 11 on which an image can be formed to a required potential, and image information (on the charged peripheral surface of the photosensitive drum 11). The exposure device 13 as an example of an electrostatic latent image forming unit that irradiates light based on a signal to form an electrostatic latent image (for each color) having a potential difference, and the corresponding color (Y , M, C, K) developing device 14 (Y, M, C, K) as an example of a developing unit that develops a toner image by developing with toner of developer 4 and intermediate transfer device 20 The primary transfer device 15 (Y, M, C, K) as an example of the primary transfer means for transferring to the toner, and the adhering matter such as toner remaining on the image holding surface of the photosensitive drum 11 after the primary transfer are removed. Drum cleaning device 16 (Y, M, C, K) or the like for cleaning. In FIG. 1, reference numerals indicating the photosensitive drum 11, the charging device 12, and the like are attached only to the yellow (Y) image forming device 10Y and omitted in the other image forming devices 10 (M, C, K). To do.

  The photosensitive drum 11 is formed by forming an image holding surface having a photoconductive layer (photosensitive layer) made of a photosensitive material on the peripheral surface of a cylindrical or columnar base material to be grounded. The photosensitive drum 11 is supported so as to rotate in a direction indicated by an arrow A when power is transmitted from a driving device (not shown).

  The charging device 12 includes a contact-type charging roll that is disposed in contact with the photosensitive drum 11. The charging device 12 has a cleaning roll 121 that cleans its surface. A charging voltage is supplied to the charging device 12. As the charging voltage, when the developing device 14 performs reversal development, a voltage or current having the same polarity as the charging polarity of the toner supplied from the developing device 14 is supplied.

  The exposure device 13 irradiates the photosensitive drum 11 with light corresponding to image information by LEDs (Light Emitting Diodes) as a plurality of light emitting elements arranged along the axial direction of the photosensitive drum 11 to electrostatic latent images. The LED print head is formed. As the exposure device 13, a device that deflects and scans laser light configured according to image information along the axial direction of the photosensitive drum 11 may be used.

  As shown in FIG. 2, each of the developing devices 14 (Y, M, C, K) holds the developer 4 inside a housing 140 in which an opening and a storage chamber for the developer 4 are formed. A developing roll 141 that conveys the developer 4 to a developing area facing the photosensitive drum 11, two agitating and conveying members 142 and 143 such as two screw augers that convey the developer 4 while passing the developing roll 141 while stirring, and a developing roll 141. A layer thickness regulating member 144 that regulates the amount (layer thickness) of the developer held on the substrate is arranged. A developing bias voltage is supplied to the developing device 14 between a developing roll 141 and the photosensitive drum 11 from a power supply device (not shown). Further, the developing roll 141 and the agitation transport members 142 and 143 are rotated in a required direction by receiving power from a driving device (not shown). Further, as the four-color developer 4 (Y, M, C, K), a two-component developer containing a non-magnetic toner and a magnetic carrier is used.

  The primary transfer device 15 (Y, M, C, K) is in contact with the periphery of the photosensitive drum 11 via an intermediate transfer belt 21 and rotates, and a contact type provided with a primary transfer roll to which a primary transfer voltage is supplied. This is a transfer device. As the primary transfer voltage, a DC voltage having a polarity opposite to the charging polarity of the toner is supplied from a power supply device (not shown).

  As shown in FIG. 2, the drum cleaning device 16 is disposed so as to be in contact with the peripheral surface of the photosensitive drum 11 after the primary transfer with a container-shaped main body 160 that is partially opened at a required pressure. A cleaning plate 161 that removes and removes deposits such as toner, and a sending member 162 such as a screw auger that collects and removes deposits such as toner removed by the cleaning plate 161 and sends them to a collection system (not shown). ing. As the cleaning plate 161, a plate-like member (for example, a blade) made of a material such as rubber is used.

  As shown in FIG. 1, the intermediate transfer device 20 is arranged to be present at a position above each image forming device 10 (Y, M, C, K). The intermediate transfer device 20 includes an intermediate transfer belt 21 that rotates in a direction indicated by an arrow B while passing a primary transfer position between the photosensitive drum 11 and the primary transfer device 15 (primary transfer roll), and an intermediate transfer belt 21. Are arranged on the outer peripheral surface (image holding surface) side of the intermediate transfer belt 21 supported by the belt support roll 22 and a plurality of belt support rolls 22 to 25 that hold the belt in a desired state from the inner surface thereof and rotatably support the belt. The secondary transfer device 26 as an example of a secondary transfer means for secondary transfer of the toner image on the intermediate transfer belt 21 to the recording paper 5 and the outer peripheral surface of the intermediate transfer belt 21 after passing through the secondary transfer device 26 And a belt cleaning device 27 that removes and adheres toner, paper dust, and other adhering matter.

  As the intermediate transfer belt 21, for example, an endless belt made of a material in which a resistance adjusting agent such as carbon black is dispersed in a synthetic resin such as polyimide resin or polyamide resin is used. Further, the belt support roll 22 is configured as a back support roll for secondary transfer, the belt support roll 23 is configured as a drive roll that is rotationally driven by a driving device (not shown), and the belt support roll 24 is configured to form an image on the intermediate transfer belt 21. The belt support roll 25 is configured as a tension applying roll that applies tension to the intermediate transfer belt 21.

  As shown in FIG. 1, the secondary transfer device 26 is configured to move the intermediate transfer belt 21 at a secondary transfer position that is an outer peripheral surface portion of the intermediate transfer belt 21 supported by the belt support roll 22 in the intermediate transfer device 20. It is a contact type transfer device provided with a secondary transfer roll that rotates in contact with a peripheral surface and is supplied with a secondary transfer voltage. The secondary transfer roll 26 or the support roll 22 of the intermediate transfer device 20 is supplied with a DC voltage having a polarity opposite or the same as the charging polarity of the toner as a secondary transfer voltage from a power supply device (not shown).

  As shown in FIG. 1, the belt cleaning device 27 is disposed so as to be in contact with a container-shaped main body 270 that is partially opened and a peripheral surface of the intermediate transfer belt 21 after the secondary transfer with a required pressure. A cleaning plate 271 that removes and removes adhering matter such as residual toner, and a sending member 272 such as a screw auger that collects and removes adhering matter such as toner removed by the cleaning plate 271 and sends it to a collecting device (not shown). Has been. As the cleaning plate 271, a plate-like member (for example, a blade) made of a material such as rubber is used.

  The fixing device 50 according to the present embodiment rotates in a direction indicated by an arrow and maintains a surface temperature at a predetermined temperature inside a housing (not shown) in which an inlet and an outlet of the recording paper 5 are formed. A belt-shaped or roll-shaped heating rotator (heating member) 51 heated by a heating source, and a belt shape rotating in contact with a predetermined pressure in a state substantially along the axial direction of the heating rotator 51 A plurality of pressurizing rotary bodies (pressurizing members) 52, 53 and the like in a roll form are arranged. In the fixing device 50, a contact portion where the heating rotator 51 and the pressing rotators 52 and 53 come into contact is a fixing processing unit that performs a required fixing process (heating and pressing). The configuration of the fixing device 50 according to the present embodiment will be described in detail later.

  The paper feeding device 30 is disposed so as to exist at a lower position along the vertical direction of the image forming device 10 (Y, M, C, K). The paper feeding device 30 includes a plurality (or a single number) of paper storage bodies 31 for storing recording papers 5 of a desired size and type, and sending out the recording paper 5 from the paper storage bodies 31 one by one. It is mainly composed of the device 32. The paper container 31 is attached, for example, so that it can be pulled out to the front side (side surface on which the user faces during operation) of the apparatus main body 1a by a guide rail (not shown). In this embodiment, the front side surface in the direction orthogonal to the drawing is set to be the front surface of the apparatus main body 1a.

  Examples of the recording paper 5 include thin paper such as plain paper and tracing paper used for electrophotographic copying machines and printers, or an OHP sheet. In order to further improve the smoothness of the image surface after fixing, the surface of the recording paper 5 is preferably as smooth as possible. For example, coated paper in which the surface of plain paper is coated with resin, art paper for printing, etc. So-called cardboard having a relatively large basis weight can be suitably used.

  As shown in FIG. 1, between the paper feeding device 30 and the secondary transfer device 26, a pair of one or a plurality of paper transporting rolls that transport the recording paper 5 delivered from the paper feeding device 30 to the secondary transfer position. 33 and a paper feed conveyance path 34 constituted by a conveyance guide (not shown) are provided along the vertical direction on the left side surface of the apparatus main body 1a. The pair of sheet conveyance rolls 33 arranged at the position immediately before the secondary transfer position in the sheet conveyance path 34 is configured as a roll (registration roll) that adjusts the conveyance timing of the recording sheet 5, for example. Further, between the secondary transfer device 26 and the fixing device 50, a paper transport path 35 for transporting the recording paper 5 after the secondary transfer sent from the secondary transfer device 26 to the fixing device 50 is provided. Yes. Further, in a portion close to the discharge port of the sheet formed on the apparatus main body 1a, the recording sheet 5 after fixing fed from the fixing device 50 by the exit roll 36 is fed to the first sheet discharge portion 37 on the upper part of the image forming apparatus main body 1a. A first paper discharge path 39 having a first paper discharge roll pair 38 for discharging to a second paper discharge roll and a second paper discharge roll for discharging to a second paper discharge section 43 located above the first paper discharge section 37. A second discharge conveyance path 45 having a pair 44 is provided. Further, the discharge direction of the recording paper 5 is switched to the second discharge conveyance path 45 by the first switching gate G1, and the third paper discharge roll for discharging to the third paper discharge portion 46 on the left side surface of the apparatus main body 1a. A pair 47 is provided. The third paper discharge unit 46 is a so-called face-up tray that discharges with the image side facing up.

  Between the fixing device 50 and the first paper discharge roll pair 38, a second switching gate G2 for switching the paper conveyance path is provided. The first paper discharge roll pair 38 is configured such that its rotation direction can be switched between a normal rotation direction (discharge direction) and a reverse rotation direction. When images are formed on both sides of the recording paper 5, the rear end of the recording paper 5 on which the image is formed on one side passes through the second switching gate G2, and then the rotation direction of the first paper discharge roll pair 38 is corrected. Switch from the rolling direction (discharge direction) to the reverse direction. The recording sheet 5 conveyed in the reverse direction by the first sheet discharge roll pair 38 is switched on the conveyance path by the second switching gate G2, and is formed on both sides formed along the side surface of the apparatus main body 1a along the substantially vertical direction. It is conveyed to the conveyance path 48 for use. The duplex conveyance path 48 includes a sheet conveyance roll pair 49 that conveys the recording sheet 5 to the sheet conveyance roll pair 33 in a state where the front and back sides are reversed, a conveyance guide (not shown), and the like. Reference numeral 49a denotes a pair of paper transporting rolls that transports the recording paper 5 fed from a paper container 31 positioned below or a manual feed tray (not shown) to the pair of paper transporting rolls 33.

  In FIG. 1, reference numeral 145 (Y, M, C, K) is arranged along the direction orthogonal to the paper surface, and includes at least toner supplied to the corresponding developing device 14 (Y, M, C, K). Each of the toner cartridges containing the agent is shown. In this embodiment, a developer 4 in which toner and carrier are mixed is accommodated in a toner cartridge 145 (Y, M, C, K). Reference numeral 70 denotes a unitized yellow (Y), magenta (M), cyan (C), and black (K) image forming device 10Y, 10M, 10C, or 10K attached to or detached from the device main body 1a. The guide member which guides in the case is shown.

  Further, reference numeral 200 in FIG. 1 indicates a control device that comprehensively controls the operation of the image forming apparatus 1. The control device 200 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a bus connecting these CPU and ROM, a communication interface, and the like (not shown).

<Operation of Image Forming Apparatus>
Hereinafter, a basic image forming operation by the image forming apparatus 1 will be described.

  Here, a full-color image is formed by using the four image forming devices 10 (Y, M, C, K) to form a full-color image configured by combining four color (Y, M, C, K) toner images. The operation in the mode will be described.

  When the image forming apparatus 1 is controlled by the control apparatus 200 and receives command information of a request for a full-color image forming operation (printing) from a user interface (not shown), a printer driver, or the like, the four image forming apparatuses 10 (Y, M, C, K), the intermediate transfer device 20, the secondary transfer device 26, the fixing device 50, etc. are started.

  In each image forming apparatus 10 (Y, M, C, K), as shown in FIGS. 1 and 2, each photosensitive drum 11 is first rotated in a direction indicated by an arrow A, and the present embodiment. Each charging device 12 according to the method charges the surface of each photosensitive drum 11 to a required polarity (negative polarity in the first embodiment) and a potential. Subsequently, the exposure apparatus 13 converts the image information input to the image forming apparatus 1 into each color component (Y, M, C, K) with respect to the surface of the photosensitive drum 11 after charging. The light emitted on the basis of the signal is irradiated to form an electrostatic latent image of each color component composed of a required potential difference on the surface.

  Subsequently, each image forming device 10 (Y, M, C, K) corresponds to the electrostatic latent image of each color component formed on the photosensitive drum 11 charged to a required polarity (minus polarity). Color (Y, M, C, K) toner is supplied from the developing roll 141 and electrostatically attached to perform development. By this development, the electrostatic latent images of the respective color components formed on the respective photosensitive drums 11 are visualized as toner images of four colors (Y, M, C, K) respectively developed with the corresponding color toners. It becomes.

  Subsequently, when each color toner image formed on the photosensitive drum 11 of each image forming device 10 (Y, M, C, K) is conveyed to the primary transfer position, the primary transfer device 15 (Y, M, C, K) are primarily transferred in such a manner that the toner images of the respective colors are sequentially superimposed on the intermediate transfer belt 21 that rotates in the direction indicated by the arrow B of the intermediate transfer device 20.

  Further, in each image forming device 10 (Y, M, C, K) for which the primary transfer has been completed, the drum cleaning device 16 removes the adhering matter so as to clean the surface of the photosensitive drum 11. Thereby, each image forming device 10 (Y, M, C, K) is brought into a state in which the next image forming operation is possible.

  Subsequently, in the intermediate transfer device 20, the toner image primarily transferred by the rotation of the intermediate transfer belt 21 is held and conveyed to the secondary transfer position. On the other hand, the paper feeding device 30 sends the required recording paper 5 to the paper feeding conveyance path 34 in accordance with the image forming operation. In the paper feed conveyance path 34, a pair of paper conveyance rolls 33 as registration rolls feeds the recording paper 5 to the secondary transfer position in accordance with the transfer timing.

  At the secondary transfer position, the secondary transfer device 26 performs secondary transfer of the toner image on the intermediate transfer belt 21 onto the recording paper 5 at once. Further, in the intermediate transfer device 20 after the secondary transfer is completed, the belt cleaning device 27 removes adhered matters such as toner remaining on the surface of the intermediate transfer belt 21 after the secondary transfer, and cleans it.

  Subsequently, the recording sheet 5 on which the toner image is secondarily transferred is peeled from the intermediate transfer belt 21 and then conveyed to the fixing device 50 via the sheet conveying path 35. In the fixing device 50, a necessary fixing process (heating) is performed by introducing and passing the recording sheet 5 after the secondary transfer through a contact portion between the rotating heating rotating body 51 and the pressing rotating bodies 52 and 53. And an unfixed toner image is fixed on the recording paper 5. Finally, the recording paper 5 after fixing is completed, for example, on the upper portion of the apparatus main body 1a by the first paper discharge roll pair 38 or the like during the image forming operation only for forming an image on one side thereof. The paper is discharged to the first paper discharge unit 37 installed.

  Through the above operation, the recording paper 5 on which a full color image formed by combining four color toner images is output. Note that the image forming apparatus 1 may naturally form a monochrome image on the recording paper 5 using only the black (K) image forming apparatus 10K.

<Configuration of fixing device>
3 and 4 show the fixing device according to the first embodiment. FIG. 3 shows the entire fixing device, and FIG. 4 shows the main part of the fixing device.

  As shown in FIGS. 3 and 4, the fixing device 50 is roughly divided into an endless heating belt 51 as an example of a rotating body for heating (heating member), and a plurality of pressurizing members that are in pressure contact with the heating belt 51. A pressure belt 52 and a pressure roll 53 are provided as an example of a rotating body (pressure member). The pressure belt 52 corresponds to a first pressure member, and the pressure roll 53 corresponds to a second pressure member. In the fixing device 50, the pressure contact portion where the heating belt 51, the pressure belt 52 and the pressure roll 53 are in pressure contact constitutes a fixing processing portion (nip portion) N that performs a required fixing process (heating and pressing). . The fixing device 50 includes a plurality of first and second nip portions N1 and N2 according to the number of pressure rotating bodies (two in the illustrated example).

  When the recording paper 5 holding the unfixed toner image T enters the nip portions N1 and N2 and the recording paper 5 is heated and pressurized and the temperature rises, the fixing device 50 rapidly changes the unfixed toner image T. Thus, the temperature rise is suppressed and generation of a volatile organic compound (VOC) from the unfixed toner image T is suppressed. Therefore, the fixing device 50 includes a plurality of pressure rotators including a pressure belt 52 and a pressure roll 53 as pressure rotators. Moreover, the fixing device 50 is a pressure rotating body disposed on the upstream side in the conveyance direction of the recording paper 5, and can have a larger (larger) area of the nip portion N <b> 1 than the pressure roll 53. The pressure belt 52 is adopted. Therefore, the fixing device 50 sets the heating temperature of the heating belt 51 to a relatively high temperature and relatively heats the unfixed toner image T without causing the pressure belt 52 to relatively increase the area of the nip portion N1. It can be widely used, and fixing ability can be ensured. However, a pressure roll may be arranged on the upstream side in the conveyance direction of the recording paper 5 as long as it is a configuration capable of suppressing a rapid temperature rise of the unfixed toner image T.

  Further, the pressure belt 52 disposed on the upstream side in the conveyance direction of the recording paper 5 has a relatively large area of the nip portion N1. Therefore, in order to ensure the fixability without abruptly increasing the fixing temperature, it is desirable to press the pressure belt 52 against the heating belt 51 with a relatively high pressure compared to the pressure roll 53. Therefore, the fixing device 50 has a plurality of pressure members, and the pressures of the plurality of pressure members are set to different values, that is, pressure disposed on the upstream side in the conveyance direction of the recording paper 5. The pressing force of the belt 52 is set to be relatively high (strong), and the pressing force of the pressure roll 53 disposed on the downstream side in the conveyance direction of the recording paper 5 is set to be relatively low (weak). However, in this embodiment, as will be described later, the heating belt 51 is driven by the pressure roll 53, and the pressure belt 52 is driven to rotate as the heating belt 51 moves. The pressing force of the pressure roll 53 and the pressure belt 52 is set so as to satisfy the driving relationship.

  As shown in FIG. 5, for example, the heating belt 51 is made of a material in which a resistance adjusting agent such as carbon black is dispersed in a synthetic resin having heat resistance such as polyimide resin or polyamide resin. An endless belt is used. The heating belt 51 is a rotating body that circulates and is shown in FIG. 5 in a shape that follows the state of use for convenience. However, in the free state, the heating belt 51 has a cylindrical shape. As shown in FIG. 3, the heating belt 51 is driven to rotate in accordance with the pressure applied by the pressure roll 53 that is rotationally driven by a drive motor 54 as a drive source. At the time of fixing, the heating belt 51 is rotationally driven so as to circulate and move at a fixing speed (for example, 200 to 300 mm / sec) determined in advance by the pressure roll 53.

  The heating belt 51 has a significantly smaller heat capacity than a heating roll, which is a roll-shaped heating rotating body, and is heated to a required fixing temperature in a short time by a heating unit 58 described later. Therefore, when the start signal of the image forming operation is input, the heating belt 51 can reach the required fixing temperature and start the fixing operation in a single hour.

  As shown in FIG. 6, the heating belt 51 is rotatably held by a pair of belt end holding members 55 and 56 respectively arranged at both ends along the axial direction (direction intersecting the moving direction). ing. The pair of belt end holding members 55 and 56 are inserted into both end portions along the axial direction of the heating belt 51 and have a substantially elliptical outer peripheral surface that holds the heating belt 51 rotatably. Parts 551 and 561 (see FIG. 3), and flange parts 552 and 562 provided integrally at both ends of the holding parts 551 and 561 in a direction intersecting the axial direction of the heating belt 51. The pair of belt end holding members 55 and 56 are attached to a casing (frame) of the fixing device 50 (not shown) via flange portions 552 and 562. The interval between the flange portions 552 and 562 of the belt end holding members 55 and 56 is set slightly longer than the length along the axial direction of the heating belt 51. Therefore, the fixing device 50 is prevented from being damaged by the end portions of the heating belt 51 along the axial direction being pressed against the flange portions 552 and 562 of the belt end holding members 55 and 56.

  As shown in FIG. 3, the heating belt 51 includes a supporting member 57 that supports a pair of belt end holding members 55 and 56 connected to each other, and the heating belt 51 attached to the supporting member 57. Heating means 58 for heating from the inside is provided.

  The support member 57 is formed in a substantially U shape toward the side (left side in the figure) with a metal such as stainless steel or a synthetic resin having heat resistance. The support member 57 is a member having rigidity to receive the pressure applied by the pressure belt 52 and the pressure roll 53. A heating means 58 is attached to the support member 57. The heating means 58 is attached to a heating base 581 formed of a heat-resistant synthetic resin or the like as a rigid body having a substantially rectangular cross section, and a pressure side surface (left side in the figure) of the heating base 581. And a planar heating member 582. The heating base material 581 is fitted into the support member 57 via the recesses 583 and 584 or attached to the support member 57 by means such as screwing (not shown). The heating base 581 has three convex portions 585a and 585 that extend along the axial direction (longitudinal direction) of the heating belt 51 and hold the heat generating member 582 in a planar shape on the side surface on the nip portion N1, N2 side. 586. As shown in FIG. 3, the first convex portion 585 arranged on the upstream side in the moving direction of the heating belt 51 is a pressurizing belt that pressurizes the pressure belt 52 in the first nip portion N1. It is located on the downstream side along the moving direction of the pressure belt 52 so as to face the pressure plate 523. The second convex portion 586 arranged on the downstream side along the moving direction of the heating belt 51 corresponds to the pressing position of the pressure roll 53. Further, the first and second convex portions 585 and 586 are provided substantially corresponding to the positions of the flat plate portions 571 and 572 bent toward the side of the support member 57.

  The heat generating member 582 includes a heat generating layer 587 that is uniformly provided in a state where heat generating wires and the like are insulated, and a temperature-equalizing metal plate 588 laminated on the inner surface of the heat generating layer 587. The heat generating layer 587 generates heat in a planar shape over the entire area of the nip portions N1 and N2 when energized from a power supply device (not shown). The heat generation layer 587 is fixed to the support member 57 at both ends along the rotation direction of the heating belt 51. Further, the temperature- equalizing sheet metal 588 is fixed to the support member 57 at the upstream end along the rotation direction of the heating belt 51.

  A temperature sensor 589 as an example of a temperature detection unit is disposed on the inner surface of the temperature equalizing sheet metal 588 so as to contact an end portion on the downstream side of the first nip portion N1. The heat generating member 582 adjusts the heating belt 51 to a required fixing temperature by controlling the energization to the heat generating layer 587 based on the detection signal from the temperature sensor 589 by the control device 200. A plurality of required fixing temperatures may be set according to the type and size of the recording paper 5. In FIG. 3, reference numeral 590 indicates a signal line of the temperature sensor 589.

  Further, between the first nip portion N1 and the second nip portion N2, a press having a substantially T-shaped cross section made of an elastic body such as a heat resistant rubber supporting the back surface of the heating belt 51 or a heat resistant resin. A member 591 is disposed.

  The support member 57 is a nonwoven fabric or sponge impregnated with a liquid lubricant (oil) applied to the inner surface of the heating belt 51 in order to reduce the sliding resistance between the heating belt 51 and the sheet-like base material 587 of the heating member 582. A lubricant application member 592 made of, for example, is provided at the upstream end along the rotation direction of the heating belt 51.

  Similar to the heating belt 51, the pressure belt 52 is an endless belt made of a material in which a resistance adjusting agent such as carbon black is dispersed in a synthetic resin such as polyimide resin or polyamide resin as necessary. used. The pressure belt 52 is set to have a shorter circumference (peripheral length along the moving direction) than the heating belt 51. The pressure belt 52 is rotatably mounted on the outer periphery of a pressure member 521 that presses the pressure belt 52 against the heating belt 51 and rotatably holds the pressure belt 52 so as to circulate.

  The pressure member 521 has a substantially trapezoidal cross section made of metal, heat-resistant synthetic resin, or the like. An elastic member 522 made of heat-resistant rubber or the like is provided on the side surface of the pressing member 521 on the heating belt 51 side. The pressing member 521 is pressed against the heating belt 51 by a pressing plate 523 made of a sheet metal having a substantially L-shaped cross section disposed on the back side thereof. The pressure plate 523 is set such that the length along the axial direction of the pressure belt 52 is longer than that of the pressure belt 52. At both ends along the longitudinal direction of the pressure plate 523, as shown by hatching in FIG. 3, a pressure unit 524 that pressurizes the pressure belt 52 to press against the heating belt 51 by a support member described later. Is provided. The pressure member 521 is formed with a recess 525 that inserts a pressure plate 523 and directly presses a position near the nip portion N1.

  The pressure roll 53 includes a metal core 531 formed in a columnar shape, and an elastic body layer 532 made of a heat-resistant elastic body coated on the outer periphery of the core 531. Both ends of the core metal 531 protrude from end portions along the axial direction of the pressure roll 53 and also serve as a rotating shaft. The core metal 531 is rotationally driven by the drive motor 54 via a gear or the like (not shown) provided at one end along the axial direction.

  The both ends of the pressure belt 52 and the pressure roll 53 along the axial direction are moved in a direction in which the pressure belt 52 and the pressure roll 53 are pressed toward the heating belt 51 as shown in FIG. A lever unit 60 as an example of a support member that is freely supported is disposed. The lever units 60 respectively disposed at both end portions along the axial direction of the pressure belt 52 and the pressure roll 53 are configured similarly. The lever unit 60 includes a first support lever 61 as an example of a first support member, a second support lever 62 as an example of a second support member, and a third support lever 63 as an example of a third support member. I have.

  The pressure member 521 that holds the pressure belt 52 is supported by the first support lever 61 so as to be in pressure contact with the heating belt 51. As shown in FIGS. 7 to 9, the first support lever 61 is rotatably attached to a frame (not shown) of the fixing device 50 around a support shaft 64 as a fulcrum. As shown in FIG. 9, the first support lever 61 is formed into a substantially rectangular flat plate shape by punching a sheet metal into a required shape and performing a bending process or a welding process. An insertion hole 611 through which the support shaft 64 is rotatably inserted is opened at the base end portion of the first support lever 61. In addition, an annular recess 614 for mounting the flange portion 613 of the bearing washer 612 that rotatably supports the support shaft 64 is provided on the outer periphery of the insertion hole 611 at the base end portion of the first support lever 61. . The intermediate portion 615 of the first support lever 61 is formed in a substantially rectangular shape having a relatively wide width in order to increase rigidity. A pressing piece 616 for pressing the pressure belt 52 is provided near the base end portion of the intermediate portion 615 in a state of being bent in a plane L shape in a direction intersecting the surface of the first support lever 61. Yes. The pressing piece 616 is locked to the pressure member 521 by a locking portion (not shown). When the first support lever 61 rotates in the direction away from the nip portion N1, the pressure member 521 is 1 Separated with the support lever 61. As described above, the pressing piece 616 of the first support lever 61 presses the pressing portion 524 of the pressing plate 523 that pressurizes the pressing belt 52. In addition, the middle portion 615 of the first support lever 61 has an elongated hole 617 for allowing movement of a support shaft 651 of a cam follower 65 attached to a third support lever 63 described later at an end near the tip. Is opened diagonally. Further, a flat plate-like operating arm 618 with which one end of a first urging member for rotating the first support lever 61 is brought into contact with the distal end portion of the first support lever 61 is substantially horizontal. It is provided to extend. The operating arm 618 is formed by bending a sheet metal constituting the first support lever 61 or welding a sheet metal different from the first support lever 61. On the lower surface of the operating arm 618, a protrusion 618a for positioning a first coil spring described later is provided.

  As shown in FIG. 7B, the pressure roll 53 is rotatably mounted on a second support lever 62 as a second support member via a bearing member (not shown) in a retaining state. As shown in FIG. 10, the second support lever 62 is rotatably mounted around the same support shaft 64 as the first support lever 61 in a state where the first support lever 61 is housed inside. As shown in FIG. 10 and FIG. 11, the second support lever 62 punches a sheet metal into the same shape on the left and right via a strip-shaped connecting portion 621, and bends so that the left and right punched portions are positioned in parallel to each other. Is applied to form a substantially rectangular front surface. Circular insertion holes 622 for rotatably supporting the support shaft 64 at the same position as the first support lever 61 are opened at the base end portion of the second support lever 62. The intermediate portion 623 of the second support lever 62 is formed in a substantially rectangular shape having a relatively wide width. Further, concave portions 624 and 624 for mounting a bearing member (not shown) for rotatably supporting the pressure roll 52 are provided in a substantially semicircular shape near the tip of the intermediate portion 623 of the second support lever 62. Yes. Further, the interference with the pressure member 524 of the pressure plate 523 that pressurizes the pressure belt 52 is avoided near the base end of the intermediate portion 623 of the second support lever 62 (the movement of the pressure member 524 is allowed). ) Slit-shaped concave grooves 625 and 625 are formed. Further, a flat plate-like operating arm 626 on which a pressing force of a second urging member (described later) that urges the second support lever 62 acts is provided at the tip of the second support lever 62. The operating arm 626 is provided integrally by bending, or formed by welding or the like as a separate member. The operating arm 626 has an insertion hole 627 into which a pin (not shown) for positioning and fixing the second urging member is inserted. In addition, recesses 628 and 628 for avoiding a shaft 651 that rotatably supports the cam follower 65 are provided on the side surface opposite to the recesses 624 and 624 at the tip of the second support lever 62.

  As shown in FIG. 10, the third support lever 63 is positioned between the first support lever 61 located on the innermost side and the second support lever 62 located on the outermost side. The levers 61 and 62 are attached so as to be rotatable about the same support shaft 64. As shown in FIGS. 10 and 12, the third support lever 63 is a flat plate-shaped first and second plates that are subjected to pressing forces of first and second urging members, which will be described later, on a sheet metal punched into the same shape on the left and right. By connecting to each other by welding or the like via the second operating arms 631 and 632, the front is formed in a substantially crank shape. At the base end portion of the third support lever 63, circular insertion holes 633 for rotatably supporting the support shaft 64 at the same position as the first and second support levers 61 and 62 are opened. The intermediate portion 634 of the third support lever 63 is formed in a substantially rectangular shape having a relatively narrow width. Further, a portion on the front end side of the intermediate portion 634 is formed in a shape protruding in a substantially trapezoidal shape toward the side opposite to the support shaft 64. An intermediate portion 634 of the third support lever 63 is provided so that the first operating arm 631 protrudes laterally at the tip (left end portion in the drawing) of the region protruding in a substantially trapezoidal shape. . In addition, in the intermediate portion 634 of the third support lever 63, insertion holes 635 through which a rotation shaft 651 for rotatably supporting the disc-shaped cam follower 65 is opened. Furthermore, a second operating arm 632 is provided on the side surface opposite to the support shaft 64 at the tip end portion 636 protruding upward from the third support lever 63.

  As shown in FIGS. 6, 10, and 13, the first, second, and third support levers 61, 62, and 63 are arranged with the first support lever 61 at the innermost side, The third support lever 63 is arranged on the outer side and the second support lever 62 is arranged on the outer side of the third support lever 63, so that each of the support levers 61, 62, 63 is independent about the support shaft 64. So that it can rotate freely.

  As shown in FIG. 4, the support shaft 64 that rotatably supports the first, second, and third support levers 61, 62, and 63 has a recording paper 5 that is a required distance from the first nip portion N1. Is located at a position separated from the upstream side in the conveyance direction, relatively close to the conveyance position of the recording paper 5, and slightly separated from the core 531 of the pressure roll 53 toward the back side.

  As shown in FIG. 4, a first coil spring 66 as an example of a first urging member is provided between the operating arm 618 of the first support lever 61 and the first operating arm 631 of the third support lever 63. Is installed in a compressed state. The first support lever 61 is biased clockwise by a first coil spring 66 in the drawing. Further, a second coil spring 67 as an example of a second urging member is compressed between the operating arm 626 of the second support lever 62 and the second operating arm 632 of the third support lever 63. It is installed. The second support lever 62 is urged clockwise by a second coil spring 67 in the drawing.

  These first to third support levers 61, 62, and 63 are disposed so as to be rotatable about the support shaft 64, and constitute a kind of lever. The distance L1 from the fulcrum that is the center of the support shaft 64 to the position 68 (first action point) at which the first support lever 61 presses the pressure belt 52 is the distance L1 (the distance to the perpendicular line below the first action point). 4, a distance L2 from the support shaft 64 to a position 69 (second action point) at which the second support lever 62 presses the pressure roll 53 (up to a perpendicular line below the second action point). The distance is set shorter than

  Further, the distance LF1 (the distance to the perpendicular line below the first force point) to the position 71 (first force point) where the first coil spring 66 biases the first support lever 61 is as shown in FIG. Furthermore, it is much longer than the distance L1 from the support shaft 64 to the position 68 (first action point) where the first support lever 61 presses the pressure belt 52 (the distance to the perpendicular line below the first action point). Is set. Further, the distance LF2 (the distance to the perpendicular line below the second force point) from the support shaft 64 to the position 72 (second force point) where the second coil spring 67 biases the second support lever 62 is the support shaft. A distance L2 from 64 to a position 69 (second action point) at which the second support lever 62 presses the pressure belt 52 is set to be longer than a distance L2 (distance to a perpendicular line extending from the second action point). The direction in which the first coil spring 66 biases the first support lever 61 is inclined with respect to the circumferential direction of the first support lever 61 by an angle θ. Therefore, the force F1 that the first coil spring 66 urges the first support lever 61 in the rotation direction is a value obtained by multiplying the elastic force itself of the first coil spring 66 by cos θ. On the other hand, the direction in which the second coil spring 67 biases the second support lever 62 is substantially the same as the circumferential direction of the second support lever 62. Therefore, the force F <b> 3 that the second coil spring 67 biases the second support lever 62 has a value substantially equal to the elastic force of the second coil spring 67.

According to the lever principle, for the first support lever 61,
LF1 × F1 = L1 × F2
The relationship becomes true. Here, LF1 is the distance between the support shaft 64 and the force point 71 (the length of the perpendicular line drawn from the support point to the vector of the force F1), F1 is the force applied to the force point 71, and L1 is between the support shaft 64 and the action point 68. , The length of the perpendicular drawn from the fulcrum to the vector of force F 2, F 2 is the force obtained at the point of action 68.

Therefore, the force F2 acting on the action point 68 is
F2 = (LF1 / L1) × F1
It can be expressed as.
Here, the value of LF1 / L1 is a fulcrum with the distance LF1 from the fulcrum 64 to the force point 71 that receives the force urged by the first coil spring 66 in the first support lever 61 as a numerator. This means a ratio when the distance L1 from 64 to the point of action 68 where the first support lever 61 applies pressure to the heating belt 51 by the first support lever 61 is the denominator.

Similarly, according to the lever principle, for the second support lever 62,
LF2 × F3 = L2 × F4
The relationship becomes true. Here, LF2 is the distance between the support shaft 64 and the force point 72 (the length of the perpendicular line drawn from the support point to the vector of the force F3), F3 is the force applied to the force point 72, and L2 is between the support shaft 64 and the action point 69. , The length of the perpendicular drawn from the fulcrum to the vector of the force F4, F4 is the force obtained at the point of action 69.

Therefore, the force F4 acting on the action point 69 is
F4 = (LF2 / L2) × F3
It can be expressed as.
Here, the value of LF2 / L2 is a fulcrum with the distance LF2 from the fulcrum 64 to the force point 72 receiving the force urged by the second coil spring 67 in the second support lever 62 as a numerator. This means a ratio when the distance L2 from 64 to the action point 69 at which the second support lever 62 applies pressure to the heating belt 51 by the second support lever 62 is used as the denominator.
In this embodiment, since the relations L2> L1 and LF1> LF2 are satisfied, (LF1 / L) is set larger than (LF2 / L2).

  Thus, the distance L1 from the support shaft 64 to the position 68 (first action point) at which the first support lever 61 presses the pressure belt 52 is equal to the distance from the support shaft 64 to the pressure roll 53 by the second support lever 62. Is set to be shorter than the distance to the position 69 (second action point) for pressurizing. Therefore, although the pressure belt 52 depends on the elastic coefficients of the first and second coil springs 66 and 67, the pressure belt 52 is larger than the pressure roll 53 even when LF1 and LF2 have the same distance. It is pressed against the heating belt 51 by the pressure F2.

  On the back side of the third support lever 63, as shown in FIG. 4, an eccentric cam 75 for rotationally driving the third support lever 63 in the clockwise direction and the counterclockwise direction is a frame of the fixing device 50 (not shown). It is rotatably arranged in a fixed state. The eccentric cam 75 is attached in a state of being fixed to the rotary shaft 76, and is rotationally driven by a second drive motor 77 as a drive source. The eccentric cam 75 is in contact with a cam follower 65 provided rotatably on the third support lever 63.

  When attention is paid to the third support lever 63, the position where the cam follower 65 is pressed by the eccentric cam 75 is the power point, and the first and second operating arms 631 and 632 of the third support lever 63 are the first and first. The position where the two coil springs 66 and 67 are pressed is the point of action.

  In the third support lever 63, the first and second operating arms 631 and 632 from the support shaft 64 to the first and second operating arms 63 from the distance from the support shaft 64 to the force point at which the cam follower 65 is pressed by the eccentric cam 75. The distance to the action point that is the position for pressing the two-coil springs 66 and 67 is set long. Accordingly, the force with which the eccentric cam 75 presses the cam follower 65 is increased by the longer distance from the support shaft 64 to the action point, and acts on the first and second coil springs 66 and 67. Therefore, the adjustable width of the eccentric cam 75 that rotates the third support lever 63 can be increased. In addition, even if the amount of eccentricity of the eccentric cam 75 is small, the amount of eccentricity of the eccentric cam 75 can be enlarged and converted to the amount of pressing of the first and second coil springs 66 and 67.

  The third support lever 63 rotates in the clockwise direction and the counterclockwise direction following the outer peripheral shape of the eccentric cam 75 by rotationally driving the eccentric cam 75 by the second drive motor 77. When the third support lever 63 rotates, the first support lever 61 is pressed via the first coil spring 66, and the first support lever 61 applies a pressure F <b> 1 (elastic restoring force) generated by elastic deformation of the first coil spring 66. Rotate according to. Further, when the third support lever 63 rotates, the second support lever 62 is pressed via the second coil spring 67, and the second support lever 62 is applied with a pressure F 3 (elastic restoration) generated by elastic deformation of the second coil spring 67. Rotate according to force.

  As shown in FIG. 4, the eccentric cam 75 has a first curved portion 751 having the smallest outer diameter and a first inclined portion 752 whose outer diameter gradually increases along the clockwise direction. A second curved portion 753 whose outer diameter is set larger than that of the first curved portion 751, a third curved portion 754 whose outer diameter is set largest along the clockwise direction, and a clockwise direction. And a fourth curved portion 755 having an outer diameter that gradually decreases. The eccentric cam 75 is rotationally driven in a required direction at a required timing by the second drive motor 77, and stops at a required position. The rotation amount and timing of the second drive motor 77 are controlled by the control device 200. As a result, the eccentric cam 75 includes a position where the pressing force formed by the third bending portion 754 is maximum, a position where the pressing force formed by the second bending portion 753 is intermediate, and the first bending portion 751. It can be set to the pressing force release position.

<Operation of fixing device>
The image forming apparatus 11 according to this embodiment is controlled by the control device 200, and starts receiving an image forming operation request information when receiving a full color image forming operation (printing) request command from a user interface (not shown) or a printer driver. Accordingly, the fixing device 50 is driven.

  In the fixing device 50, as shown in FIGS. 3 and 4, the pressure roll 53 is rotationally driven by the drive motor 54, and the heating member 582 of the heating unit 58 is energized to heat the heating belt 51. When the pressure roll 53 is driven to rotate, the heating belt 51 and the pressure belt 52 are driven and rotated accordingly. Further, in the fixing device 50, the eccentric cam 75 is rotationally driven in the required direction by the second drive motor 77 by the required angle, and the third support lever 63 is rotated by the eccentric cam 75 through the cam follower 65 by the required angle. Rotate to stop.

  Then, in the fixing device 50, as shown in FIG. 4, the first support lever 61 rotates according to the elastic force F1 of the first coil spring 66, and the pressure belt 52 is heated by the first support lever 61. 51 is in pressure contact. In the fixing device 50, the second support lever 62 rotates according to the elastic force F <b> 3 of the second coil spring 67, and the pressure roll 53 is pressed against the heating belt 51 by the second support lever 62.

  At this time, the first support lever 61 rotates about the support shaft 64 as a fulcrum, and pressurizes the pressure belt 52 against the heating belt 51 according to the elastic force F <b> 1 generated by the deformation of the first coil spring 66. Similarly, the second support lever 62 rotates about the support shaft 64 as a fulcrum, and the pressure roll 53 is brought into pressure contact with the heating belt 51 according to the elastic force F <b> 3 generated by the deformation of the second coil spring 67.

Therefore, the fixing device 50 is based on the lever principle through the first support lever 61.
F2 = (LF1 / L1) × F1
The pressure belt 52 is brought into pressure contact with the heating belt 51 by the applied pressure F2 obtained by the following relational expression. Similarly, the fixing device 50 is based on the lever principle through the second support lever 62.
F4 = (LF2 / L2) × F3
The pressurizing roll 53 is brought into pressure contact with the heating belt 51 by the pressurizing force F4 obtained by the following relational expression.

  Here, in the above embodiment, the relationship of LF1 ≧ LF2 and L1> L2 is satisfied, and when it is assumed that F1≈F2, the pressure belt 52 is different from the pressure roll 53 and larger than the pressure roll 53. The belt is pressed against the heating belt 51 with an independently set pressure (F2> F4).

  The pressing force F2 at which the pressure belt 52 is pressed against the heating belt 51 and the pressing force F4 at which the pressure roll 53 is pressed against the heating belt 51 are described above by using the first to third support levers 61 to 63. Each of the relational expressions can be set to an independent value.

  In addition, the fixing device 50 only needs to include first to third support levers 61 to 63 incorporated in each other, and the configuration can be simplified, and the first and second support levers 61 and 62 can be made independent. Compared to the case where the rotation is performed by different eccentric cams, the configuration can be simplified and the apparatus can be prevented from being enlarged.

  In the fixing device 50, in order to release the applied pressure, the eccentric cam 75 is rotated and stopped at a position where the first curved portion 751 of the eccentric cam 75 contacts the cam follower 65. As a result, the third support lever 63 rotates counterclockwise as shown in FIG. 14, and the first and second support levers 61 and 62 also rotate counterclockwise as shown in FIG. The pressure belt 52 and the pressure roll 53 move to a retracted position separated from the heating belt 51.

[Embodiment 2]
FIG. 15 shows a fixing device according to Embodiment 2 of the present invention.

  In the fixing device 50 according to the second embodiment, as shown in FIG. 15, the support shafts of the first support lever 61 and the second support lever 62 are set at different positions. A support shaft 641 that rotatably supports the first support lever 61 is located upstream of the support shaft 64 that rotatably supports the first and third support levers 61 and 63 in the conveyance direction of the recording paper 5. It is arranged at a separated position.

  In this way, by setting the position of the support shaft 641 that rotatably supports the first support lever 61, when the first support lever 61 rotates in the direction away from the heating belt 51, the pressure belt 52 A separation distance away from the heating belt 51 can be set large. Therefore, the recording paper 5 can be easily removed even when the recording paper 5 is jammed (conveyance failure) or the like at the first and second nip portions N1 and N2.

[Embodiment 3]
FIG. 16 shows a fixing device according to Embodiment 3 of the present invention.

  In the fixing device 50 according to the third embodiment, as illustrated in FIGS. 16, 17, and 19, the urging member that urges the first support lever 61 is disposed not on the coil spring but on the support shaft 64. A torsion spring 661 as an example of a first urging member is configured. A torsion spring 661 is mounted on the outer periphery of a bearing washer 612 for mounting the first support lever 61 on the support shaft 64 in a rotatable manner. A relatively long end 662 of the torsion spring 661 is engaged with a recess 619 provided in the first support lever 61 as shown in FIG. Further, the other end 663 of the torsion spring 661 is engaged with a recess 637 provided in the third support lever 63 as shown in FIG.

  When the third support lever 63 rotates in the clockwise direction in FIG. 16, the third support lever 63 rotates in the direction in which the other end 663 of the torsion spring 6611 is tightened. Therefore, the first support lever 61 is biased in the clockwise direction in response to the clockwise rotational moment generated at the one end 662 of the torsion spring 661.

  In the third embodiment, since the first urging member is constituted by the torsion spring 661 attached to the support shaft 64, the working arm and the coil arranged in a state of protruding from the outer periphery of the first and third support levers 61 and 63 are provided. The spring 66 becomes unnecessary, and the apparatus can be downsized accordingly.

  In the above embodiment, a full-color image forming apparatus that forms toner images of four colors of yellow (Y), magenta (M), cyan (C), and black (K) has been described as the image forming apparatus. Needless to say, the present invention can be similarly applied to an image forming apparatus that forms the image.

  In the above-described embodiment, the case where the heating rotator is a heating belt and the pressurizing rotator includes a pressurizing belt and a pressurizing roll has been described. However, the present invention is not limited to this. A structure in which the body is a heating roll, a pressure rotating body is composed of a plurality of pressure rolls, a heating rotating body is a heating roll, a pressure rotating body is composed of a pressure belt and a pressure roll, or a heating rotating body is Of course, various modifications such as a configuration in which the heating belt and the pressing rotator are composed of a plurality of pressing rolls are possible, and the present invention can be applied to a fixing device having a plurality of pressing rotators. .

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 1a ... Image forming apparatus main body 11 ... Photoconductor drum 14 ... Developing device 50 ... Fixing device 51 ... Heating belt 52 ... Pressure belt 53 ... Pressure roll 61 ... First support arm 62 ... Second support arm 63 ... Third support arm 64 ... Support shaft 66 ... First coil spring 67 ... Second coil spring

Claims (8)

A heating member that is heated and rotated by a heating source;
At least first and second pressure members rotating in pressure contact with the heating member at different positions;
A first support member that movably supports the first pressure member in a direction in which the first pressure member contacts and separates from the heating member;
A second support member that movably supports the second pressurizing member in a direction of coming into contact with and separating from the heating member;
A first urging member that urges the first pressure member to press against the heating member;
A second urging member that urges the second pressure member to press against the heating member;
The first support member is urged through the first urging member, and the second support member is urged through the second urging member, and is in contact with the heating member. A third support member that is movably disposed in a separating direction;
A fixing device.   The first to third support members are rotatably supported around the same fulcrum, and a distance from the fulcrum to a force point at which the first support member receives a force urged by the first urging member. And the distance from the fulcrum to the working point at which the first support member applies pressure to the heating member by the first support member, the ratio of the second support member to the second urging force from the fulcrum Set larger than the ratio of the distance to the force point that receives the force urged by the member and the distance from the fulcrum to the point of action where the second support member applies pressure to the heating member. The fixing device according to claim 1.   The first and second support members have a distance from the fulcrum to a force point at which the first and second support members receive a force urged by the first and second urging members. 3. The fixing device according to claim 2, wherein the fixing device is set to be longer than a distance to a force point that receives a force for rotating the support member in a direction approaching the heating member.   The first and second support members are rotatably supported around different fulcrums located on the first support member side, and the fulcrum of the first support member is the first fulcrum from the fulcrum of the second support member. The fixing device according to claim 1, wherein the fixing device is spaced apart from the support member.   The fixing device according to claim 4, wherein the third support member is rotatably supported around the same fulcrum as the second support member.   The fixing device according to claim 2, wherein the first and second urging members are arranged close to each other in a tangential direction with a fulcrum of the first and second support members as a center.   The fixing device according to claim 1, wherein the first urging member includes a torsion spring disposed around the fulcrum. An image forming unit for forming an image on a recording medium;
Fixing means for fixing an image formed on the recording medium by the image forming unit;
With
An image forming apparatus using the fixing device according to claim 1 as the fixing unit.

Images