JP2008292522A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively heat a photoreceptor drum by a heater even if there is no space in which the heater is disposed on the inside or the outside of the photoreceptor drum. <P>SOLUTION: An endless intermediate transfer belt 31 is tensioned and laid on a driving roller 43 and a driven roller 44, and toner images formed on the photoreceptor drums 36 for respective colors are primarily transferred to the intermediate transfer belt at primary transfer nips T1. Planar heaters H and H are faced to the back surface 31b of the intermediate transfer belt 31 between a virtual plane S passing through the shaft centers 43a and 44a of the driving roller 43 and the driven roller 44 and a transfer part side 31a positioned on the upstream side of the driving roller 43 and on the downstream side of the driven roller 44 out of the intermediate transfer belt 31. By heating the intermediate transfer belt 31 by the heaters H and H, the photoreceptor drum 36 in contact with the intermediate transfer belt 31 is heated through the intermediate transfer belt 31. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a tandem type image forming apparatus in which a plurality of image forming stations are arranged along the rotation direction of an intermediate transfer belt.

  2. Description of the Related Art Image forming apparatuses such as printers, copiers, facsimiles, and multi-function machines of these are known that include a heater for heating a photosensitive drum (see, for example, Patent Document 1).

During image formation, the surface (outer peripheral surface) of the photosensitive drum is uniformly (uniformly) charged to a predetermined polarity and potential by a charging device. However, in a high-humidity environment, the surface potential after charging varies depending on the moisture adhering to the surface, and image flow may occur in the developed image (toner image). In Patent Document 1 described above, a heater is provided inside the photosensitive drum in order to prevent such image flow. With this heater, the photosensitive drum is directly heated from the inside to prevent moisture from adhering to the surface of the photosensitive drum, or to remove the adhering moisture. Note that the above-described image flow is a phenomenon that appears prominently when the photosensitive drum is an a-Si (amorphous silicon) drum.
Japanese Patent Laid-Open No. 9-22168

  However, according to the above-described Patent Document 1, when the image forming apparatus is a small machine, the diameter of the photosensitive drum is small, and thus it is difficult to provide a heater inside the photosensitive drum. On the other hand, it is conceivable to arrange the heater so as to face the surface outside the photosensitive drum. However, depending on the image forming apparatus, this may be difficult in terms of space. For example, in a tandem four-color full-color image forming apparatus using an intermediate transfer belt, four (four-color) image forming stations each having a photosensitive drum are sequentially arranged along the moving direction of the intermediate transfer belt. In this type of image forming apparatus, however, a charging device, a developing device, a cleaning device, and the like are disposed on the outer periphery of the photosensitive drum, and there is almost no space for the heater.

  Therefore, according to the present invention, in an image forming apparatus using an intermediate transfer belt, even when there is no space for arranging a heater inside or outside the photosensitive drum, the photosensitive drum can be effectively heated by the heater. An object of the present invention is to provide an image forming apparatus as described above.

  The invention according to claim 1 includes an intermediate transfer belt rotating endlessly and a plurality of image forming stations arranged along a rotation direction of the intermediate transfer belt, each of the image forming stations being the intermediate transfer belt. The present invention relates to an image forming apparatus having a photosensitive drum in contact with the surface of a belt and sequentially transferring toner images formed on the surfaces of the plurality of photosensitive drums onto the surface of the intermediate transfer belt. The image forming apparatus according to the present invention is characterized in that a heater for heating the intermediate transfer belt is disposed inside the intermediate transfer belt.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the heater is disposed over substantially the entire width in the belt width direction orthogonal to the rotation direction of the intermediate transfer belt. .

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the heater is a planar heater disposed so as to face the back surface of the intermediate transfer belt in a non-contact manner. Yes.

  The invention according to claim 4 is the image forming apparatus according to claim 3, further comprising a plurality of drive system rollers on which the intermediate transfer belt is stretched, and the movement of the intermediate transfer belt among the plurality of drive system rollers. A roller disposed immediately downstream of the photosensitive drum along the direction is a first roller, and a roller disposed immediately upstream of the photosensitive drum on the most upstream side is a second roller. Sometimes, the heater is disposed at a position facing the back surface of the intermediate transfer belt on the transfer portion side located upstream of the first roller and downstream of the second roller. It is a feature.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, when the plane passing through the axis of the first roller and the axis of the second roller is a virtual plane, the heater transfers the intermediate transfer. The belt is disposed between the transfer portion side of the belt and the virtual plane.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the surface of the intermediate transfer belt is arranged on the inner side of the intermediate transfer belt and presses the back surface of the intermediate transfer belt so that the surface of the intermediate transfer belt is exposed. A plurality of transfer rollers that contact the surface of the drum are provided, and the heater is disposed between the two transfer rollers adjacent to each other.

  According to a seventh aspect of the invention, in the image forming apparatus according to the sixth aspect of the invention, the heater is disposed at an approximately equal distance from the two adjacent photosensitive drums.

  According to an eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect, a plurality of the heaters are provided.

  According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, the photosensitive drum is an a-Si drum.

  According to the first aspect of the present invention, the intermediate transfer belt can be heated by the heater disposed inside the intermediate transfer belt, and when the intermediate transfer belt is rotated, a plurality of pieces in contact with the intermediate transfer belt are contacted. The photosensitive drum can be heated. For this reason, even when it is not possible to secure a space for arranging the heater near the outer peripheral surface inside or outside the photosensitive drum, the heater is arranged inside the intermediate transfer belt as described above. Thus, the photosensitive drum can be effectively heated via the intermediate transfer belt.

  According to the invention of claim 2, the heater is heated over substantially the entire width of the intermediate transfer belt in the belt width direction, and the surface of the photosensitive drum is moved along the axial direction via the heated intermediate transfer belt. It can be heated over almost the entire length.

  According to the invention of claim 3, since the heater is formed in a planar shape and is arranged so as to face the back surface of the intermediate transfer belt in a non-contact manner, for example, compared with a case where the heater is in a rod shape or the like. Thus, the intermediate transfer belt can be efficiently heated.

  According to the invention of claim 4, since the heater is disposed so as to face the back surface on the transfer portion side of the intermediate transfer belt, the back surface on the transfer portion side can be heated, and the photosensitive drum can be mounted. Can be heated.

  According to the invention of claim 5, the heater is disposed between the transfer portion side and the virtual plane in the intermediate transfer belt. That is, the entire inner side of the intermediate transfer belt is disposed on the side closer to the photosensitive drum, so that the photosensitive drum can be heated in parallel with the heating of the intermediate transfer belt. In other words, the photosensitive drum can be heated indirectly via the intermediate transfer belt and can be directly heated, so that the photosensitive drum can be efficiently heated.

  According to the sixth aspect of the invention, the heater can be disposed close to the back surface of the intermediate transfer belt, avoiding the transfer roller.

  According to the invention of claim 7, two adjacent photosensitive drums can be heated substantially evenly.

  According to the invention of claim 8, since a plurality of heaters are provided, the intermediate transfer belt can be heated in a short time.

  According to the ninth aspect of the present invention, the photosensitive drum is an a-Si drum, and an image flow is likely to occur as compared with other drums. By providing, a-Si can be heated efficiently.

  Hereinafter, the best embodiment of the present invention will be described in detail with reference to the drawings. In addition, in each drawing, the member etc. which attached | subjected the same code | symbol are the same structures, The duplication description about these shall be abbreviate | omitted suitably. Moreover, in each drawing, members and the like that are not necessary for the description are omitted as appropriate.

<Embodiment 1>
The image forming apparatus 1 according to the present invention will be described with reference to FIGS. In these drawings, the front, rear, left, right, top and bottom of the image forming apparatus 1, the intermediate transfer unit 31A, the heater H, and the like are appropriately indicated by arrows. 1 to 9, FIG. 1 is a perspective view of the entire image forming apparatus 1 as viewed from the upper left of the front side thereof. FIG. 2 is a perspective view of the entire image forming apparatus 1 as viewed from the rear and obliquely upward on the left side. FIG. 3 is a diagram schematically showing the internal structure of the image forming apparatus 1 as viewed from the left side. 4A and 4B are schematic diagrams for explaining the closed positions A1 and B1 and the open positions A2 and B2 of the front cover 3 and the transport unit 73. FIG. FIG. 5 is a perspective view of the heater member 80 as viewed obliquely from above. FIG. 6A is a perspective view of the heater member 80 attached to the attachment base 93 as viewed obliquely from above. (B) is the perspective view which looked at the same state from diagonally downward. FIG. 7 is a perspective view of the intermediate transfer unit 31A to which the heater H is attached as viewed from below with the intermediate transfer belt 31 removed. FIG. 8 is a perspective view of the intermediate transfer unit 31A to which the heater H is attached as viewed from below. FIG. 9 is a schematic view of the photosensitive drum 36, the developing device 40, the intermediate transfer belt 31 and the like as viewed from the left side.

  Here, examples of the image forming apparatus 1 include a printer, a copier, a facsimile machine, and a multifunction machine of these. In the following description, a case where the image forming apparatus 1 is a printer will be described as an example. An image forming apparatus 1 shown in FIGS. 1 to 4 is a four-color full-color image forming apparatus 1 adopting an electrophotographic system, an intermediate transfer system, and a tandem system.

  With reference to FIGS. 1 and 2, the configuration of the entire image forming apparatus 1 as viewed from the outside will be described. The image forming apparatus 1 includes a substantially box-shaped (cuboid) image forming apparatus main body 2 and a front cover 3 supported by the image forming apparatus main body 2 so as to be freely opened and closed.

  The image forming apparatus main body 2 has a front surface covered with a front cover 3 and a left side surface and a right side surface covered with a left exterior panel 4 and a right exterior panel 5 made of synthetic resin. On the rear surface of the image forming apparatus main body 2, a part 7 of a sheet metal constituting the main body frame 6 is exposed as a structure. A paper discharge tray (sheet discharge unit) 10 having a sheet stacking surface 8 is disposed on the upper surface of the image forming apparatus main body 2. The sheet stacking surface 10 is composed of an inclined surface that is gently inclined so that the rear end side is positioned higher, and a plane that continues to the rear end of the inclined surface, and is directed rearward from a sheet discharge port 11 described later after image formation. The discharged sheet is supported from below. As shown in FIGS. 1 and 2, the rear end 10 a side of the paper discharge tray 10 is supported by the image forming apparatus main body 2 so as to be swingable (openable and closable). The front end side is held in an upright posture where it is lifted by approximately 90 degrees. As a result, an intermediate transfer unit 31A, toner containers 47, 48, 50, and 51, which will be described later, can be attached and detached from above the image forming apparatus main body 2.

  The front cover 3 is provided with an operation panel 12 on the upper end side, and an openable and closable manual feed tray 13 on the front side. A touch panel type liquid crystal display unit and various buttons are arranged on the operation panel 12, and the operator stands on the front side of the image forming apparatus 1 and the entire image forming apparatus 1 is operated by the operation panel 12. Can be operated. The manual feed tray 13 is supported by the front cover 3 so as to be swingable at the lower end 13a side, and as shown by a two-dot chain line in FIG. 3, the upper end 13b side is pulled out toward the front side (arrow direction) and inclined. The upper surface 13c can be used as a manual feed tray. The entire front cover 3 is supported by the image forming apparatus main body 2 so that the lower end 3a is swingable. The closed position A1 shown in FIGS. 1 to 3 and 4A and FIG. 4B are shown. It can move between the open position A2. As shown in FIG. 2, release levers 15 with buttons 14 are provided near the left and right ends on the upper end side and the rear side of the front cover 3. A hook member (not shown) is connected to the release lever 15 via a connecting member (not shown). The hook member is disposed on the front cover 3 side. When the front cover is closed, the hook member is engaged with a locking member (not shown) on the image forming apparatus main body 2 side to lock the front cover 3. When opening the front cover 3, when the button 14 is pulled forward, the hook member is swung through the connecting member and released from the locking member, so that the lock is released. In this state, the front cover 3 can be opened by pulling the upper end side forward.

  This is the end of the description of the configuration of the entire image forming apparatus 1 viewed from the outside.

  Next, the internal structure of the image forming apparatus 1 will be described with reference to FIG. The image forming apparatus 1 includes a sheet storage unit 20, a substrate storage unit 21, an image forming unit 22, a toner supply unit 23, and a paper discharge tray (sheet discharge unit) 10 in order from the lower side to the upper side of the image forming apparatus main body 2. Is provided. A sheet conveying unit 24 is provided between the front side of the image forming apparatus main body 2 and the front cover 3.

  A sheet cassette 25 is disposed in the sheet storage unit 20. The sheet feeding cassette 25 stores a plurality of sheets in a stacked state, and biases the leading end side (the right side in the figure) of the stacked sheets upward by a lift plate 26 disposed at the bottom. Yes. As a result, the uppermost sheet in the sheet feeding cassette 25 is fed by a pickup roller 27 of a sheet transport unit 24 described later, and further, the feeding roller 28 and the retard roller 30 prevent double feeding, and only one sheet is downstream. To the side. The paper feed cassette 25 can be inserted / removed (detached) from the front side (front side) of the image forming apparatus 1. A substrate storage unit 21 is disposed above the paper feed cassette 25.

  The substrate storage unit 21 is provided with a substrate and electrical components (not shown) that control the entire image forming apparatus 1. An image forming unit 22 is disposed above the substrate storage unit 21.

  The image forming unit 22 includes an intermediate transfer belt 31 and four (four color) image forming stations aligned along the rotation direction of the intermediate transfer belt 31 (arrow R31 direction), that is, magenta (M), Image forming stations 32, 33, 34, and 35 for forming toner images with cyan (C), yellow (Y), and black (K) toners are provided. Since the four-color image forming stations 32 to 35 have the same configuration, the magenta image forming station 32 will be described below, and the description of the remaining three-color image forming stations 33 to 35 will be omitted as appropriate. .

  The intermediate transfer belt 31 is formed in an endless shape, and is stretched between the driving roller 43 and the driven roller 44. The intermediate transfer belt 31 is rotated in the direction of the arrow R31 by the rotation of the driving roller 43 in the direction of the arrow.

  The magenta image forming station 32 includes a photosensitive drum 36, a charging device 37, an exposure device 38, a developing device 40, and a primary device that are arranged around the photosensitive drum 36 in the order of rotation (arrow direction). A transfer roller 41, a drum cleaner 42, and the like are included.

  The photosensitive drum 36 is driven to rotate in the direction of the arrow at a predetermined process speed. In this embodiment, an a-Si (amorphous silicon) photosensitive drum is used as the photosensitive drum 36.

  The charging device 37 uniformly (uniformly) charges the surface of the photosensitive drum 36 to a predetermined polarity and potential.

  The exposure device 38 is constituted by, for example, a laser scanner. The exposure apparatus 38 includes a laser oscillator (not shown), a polygon mirror 38a, lenses 38b and 38c, reflection mirrors 38d, 38e, and 38f, and these are integrally incorporated to constitute an exposure unit 38A. . The exposure device 38 reflects a laser beam L emitted from a laser oscillator (not shown) based on image information sent from a personal computer (not shown) or the like by a polygon mirror 38a that rotates at high speed, and lenses 38b, Then, the light is guided to the surface of the photosensitive drum 36 after uniform charging via a mirror 38c, reflecting mirrors 38d, 38e, 38f and the like. The surface of the photosensitive drum 36 is exposed to the laser beam L to remove the charge on the exposed portion, thereby forming an electrostatic latent image.

  The developing device 40 develops the electrostatic latent image. The developing device 40 includes a developing container 40a in which a developer is accommodated, a developing sleeve 40b, developer agitating members 40c, 40d, and the like, which constitute a developing unit 40A. The developer carried on the surface of the developing sleeve 40 b is selectively attached to the electrostatic latent image on the surface of the photosensitive drum 36 by applying a developing bias between the developing sleeve 40 b and the photosensitive drum 36. This is developed as a toner image. In the present embodiment, a two-component developer mainly composed of toner and carrier is used as the developer.

  The primary transfer roller 41 transfers the toner image formed on the surface of the photosensitive drum 36 to the intermediate transfer belt 31. The primary transfer roller 41 presses the back side of the intermediate transfer belt 31 to bring the surface of the intermediate transfer belt 31 into contact with the surface of the photosensitive drum 36. As a result, a primary transfer nip T <b> 1 is formed between the surface of the intermediate transfer belt 31 and the surface of the photosensitive drum 36. The toner image formed on the surface of the photosensitive drum 36 is conveyed to the primary transfer nip T1 as the photosensitive drum 36 rotates in the arrow direction. At this time, by applying a primary transfer bias to the primary transfer roller 31, the magenta toner image on the surface of the photosensitive drum 36 is primarily transferred onto the surface of the intermediate transfer belt 31.

  The drum cleaner 42 removes toner (primary transfer residual toner) remaining on the surface of the photosensitive drum 36 without being transferred to the intermediate transfer belt 31 in the above-described primary transfer. In this embodiment, the photosensitive drum 36, the charging device 37, the drum cleaner 42, and the like are integrally configured to constitute the drum unit 36A.

  As described above, in the magenta image forming station 32, the magenta toner image formed on the surface of the photosensitive drum 36 is primarily transferred onto the surface of the intermediate transfer belt 31. Similarly, in the remaining three color (cyan, yellow and black) image forming stations 33, 34 and 35, toner images of cyan, yellow and black are formed on the surface of each photosensitive drum 36, respectively. The toner images are sequentially primary-transferred onto the intermediate transfer belt 31 by the primary transfer roller 41 and superimposed. As will be described later, these four color toner images are secondarily transferred onto the sheet all at once by applying a secondary transfer bias to the secondary transfer roller 45 at the secondary transfer nip T2. Toner remaining on the surface of the intermediate transfer belt 31 after the secondary transfer of the toner image (secondary transfer residual toner) is removed by a belt cleaner 46 disposed in the vicinity of the driven roller 44. A toner replenishing unit 23 is provided above the image forming unit 22.

  The toner replenishing unit 23 is provided with four toner containers that individually store toners of respective colors, that is, magenta, cyan, yellow, and black toner containers 47, 48, 50, and 51. The developing devices 40 of the color image forming stations 32 to 35 described above are provided with a remaining amount sensor (not shown) for detecting the remaining amount of the developer. When it is detected that the amount of the developer is less than a predetermined value, toner is supplied to the developing device 40 of each color from the toner containers 47, 48, 50, 51 of each color. Above the toner replenishing portion 23, the above-described arrangement tray 10 that can be opened and closed with respect to the rear end side is arranged.

  In the present embodiment, the sheet conveyance unit 24 is provided between the front side of the image forming apparatus main body 2 and the front cover 3, and a sheet conveyance path 52 that guides a sheet from below to above, and the sheet conveyance unit. It has a sheet re-conveying path 53 that is disposed on the front side of the path 52 and guides the sheet from the upper side to the lower side, and further has a manual feeding unit 54.

  The sheet conveyance path 52 rises upward from the vicinity of the above-described feeding roller 28, extends upward while gently curving backward, and extends upward in the vicinity of the secondary transfer nip T2 by changing the bending direction to the front. The sheet extends obliquely upward toward the rear and reaches the sheet discharge port 11. The sheet conveyance path 52 includes a rear guide 52a and a front guide 52b facing each other, and a part of the front guide 52b is formed in a conveyance unit 73 described later. In the sheet conveyance path 52, the pickup roller 27, the feeding roller 28, the retard roller 30, the conveyance roller pair 56, the registration roller pair 57, and the intermediate transfer belt 31 are sandwiched between the drive roller 43 in order from the bottom. A transfer roller 45, a fixing device (fixing unit) 58, a conveyance roller pair 60, a switching flapper 61, a paper discharge roller pair 62, and the like are provided. The above-described fixing device 58 includes a fixing roller (fixing member) 63 including a heating member (not shown), and a pressure roller (pressure member) 64 that forms a fixing nip N in pressure contact therewith. .

  The sheet fed by the pickup roller 27, the feeding roller 28, and the retard roller 30 from the sheet feeding cassette 25 is conveyed by the conveying roller pair 56 and the registration roller pair 57, and in the secondary transfer nip T2. The four color toner images on the surface of the intermediate transfer belt 31 are secondarily transferred at once, and heated and pressurized when passing through the fixing nip N to fix the four color toner images on the surface. The sheet on which the toner image has been fixed is guided to the lower surface of the switching flapper 61 by the conveying roller pair 60 and conveyed to the paper discharge roller pair 62, and is moved rearward from the sheet discharge port 11 facing the back side by the paper discharge roller pair 62. The sheet is discharged and stacked on the sheet stacking surface 8 of the sheet discharge tray 10. In the figure, the sensor flag 65 of the paper discharge sensor disposed immediately downstream of the paper discharge roller pair 62 is operating with the sheet P being discharged.

  The sheet re-conveying path 53 extends obliquely from the upper side to the front side of the above-described sheet discharge port 11, is gently curved and extends to the rear side with a steep slope, and protrudes downward at the lower end portion. Then, the sheet merges with the sheet conveyance path 52 described above. The sheet re-conveying path 53 includes a rear guide 53a and a front guide 53b that face each other. A part of the rear guide 53a is formed in a transport unit 73 described later. Further, most of the front guide 53b is incorporated inside (rear end side) of the front cover 3. In the sheet re-conveying path 53, the reverse roller pair 66, the switching flapper 61, the first, second, third and fourth re-conveying roller pairs 67, 68, 70 and 71 are arranged.

  When images are formed on both sides of the sheet, the switching flapper 61 is switched to the position indicated by the two-dot chain line, and the sheet on which the toner image is fixed is conveyed to the conveying roller pair 60 and the switching flapper 61 It is conveyed along the upper surface and further conveyed rearward by the reverse roller pair 66. Then, the rear end of the sheet passes through the conveying roller pair 60, and the reverse roller pair 66 is reversely rotated before passing through the reverse roller pair 66, and the first to fourth re-conveying roller pairs 67, 68, 70, 71 The sheet is conveyed downward and conveyed to the sheet conveyance path 52. Then, the toner image is transferred and fixed on the rear surface of the sheet in the same manner as on the front surface, and is discharged rearward from the sheet discharge port 11 and stacked on the sheet stacking surface 8 of the discharge tray 10. The A manual feed roller 72 is disposed immediately in front of the conveyance roller pair 56 in the sheet conveyance unit 24. The manual feed roller 72 feeds the sheet set on the upper surface 13c of the open manual feed tray 13 indicated by a two-dot chain line in FIG. 3 toward the conveyance roller pair 56 side.

  As shown in FIG. 3, the above-described sheet conveyance unit 24 is provided with a conveyance unit 73 that can be freely opened and closed. The transport unit 73 is disposed between the sheet transport path 52 and the sheet re-transport path 53, and a part of the front guide 52 b in the sheet transport path 52 and a part of the rear guide 53 a in the sheet re-transport path 53. And the first roller 57a of the registration roller pair 57, the secondary transfer roller 45, and the first and second rollers 70a and 71a of the third and fourth re-conveying roller pairs 70 and 71, respectively. Yes. As shown in FIGS. 4A and 4B, the transport unit 73 has a swing center on the lower end 3a side, and is supported by the image forming apparatus body 2 so as to be swingable (openable and closable). Yes.

  The transport unit 73 is opened and closed in conjunction with the opening and closing operation of the front cover 3. As shown in FIGS. 4A and 4B, the front cover 3 has a swing center 76 at the lower end, and the swing center 76 is swingably supported by the image forming apparatus main body 2. Yes. The image forming apparatus main body 2 includes a left side plate 74 and a right side plate 75 of the main body frame 6 made of a sheet metal, and extends to the front side, a part of the left side surface and the right side surface of the front cover 3 and the left side of the transport unit 73. It covers the side and the right side. A shaft 77 protrudes inwardly from the lower ends of the front end side of the left side plate 74 and the right side plate 75, and the swing center 76 of the front cover 3 is supported by the shaft 77 so as to be swingable. ing. Thereby, the front cover 3 can take the closed position A1 shown to Fig.4 (a), and the open position A2 shown to FIG.4 (b). The above-described transport unit 73 also has a swing center (not shown) on the lower end 73a side, and has a shaft (not shown) protruding inward from the left side plate 74 and the right side plate 75 on the image forming apparatus main body 2 side. It is supported so as to be able to swing. As a result, the transport unit 73 can take a closed position B1 shown in FIG. 4A and an open position B2 shown in FIG. 4B. The transport unit 73 is opened / closed in conjunction with the opening / closing operation of the front cover 3 without the operator intentionally opening / closing it. Further, when the front cover 3 and the transport unit 73 are opened, they are held at open positions A2 and B2 shown in FIG. 4B by stoppers (not shown) such as chains and links.

  In the image forming apparatus 1 described above, at the time of image formation, the hook member on the front cover 3 side is engaged with the locking member on the image forming apparatus main body 2 side, whereby the front cover 3 and the transport unit 73 are respectively shown in FIG. It arrange | positions in closed position A1, B1 shown to a). Thus, the sheet conveyance path 52 and the sheet re-conveyance path 53 are configured, and a nip is formed between each pair of rollers, so that the sheet can be conveyed.

  Here, when a jam or the like occurs during image formation, the button on the back side (see FIG. 2) at the top of the front cover 3 is operated to move the front cover 3 in the direction of arrow R3a in FIG. When opened, the transport unit 73 is also opened in conjunction with this. Thereby, as shown in FIG.4 (b), the front cover 3 and the conveyance unit 73 are each arrange | positioned in open position A2, B2. In this state, since the sheet conveyance path 52 and the sheet re-conveyance path 53 are largely opened and exposed, it is possible to easily find and remove jammed paper. After the jam processing, when the front cover 3 is moved in the direction of arrow R3b in FIG. 4B, the transport unit 73 is also moved in the same direction in conjunction with this, and the front cover 3 and the transport unit 73 are in the closed position. Arranged at A1 and B1. Thereby, it is possible to resume image formation.

  This completes the description of the internal structure of the image forming apparatus 1.

  In the image forming apparatus 1 described above, moisture may adhere to the surface of the photosensitive drum 36 in a high humidity environment. In this case, the resistance of the portion to which the moisture has adhered becomes low, and thus the photosensitive drum is charged during charging. Variations occur in the surface potential of 36, and image flow occurs in the developed toner image.

  Therefore, in the present invention, in order to prevent such image flow, a heater H is provided inside the intermediate transfer belt 31 to warm the photosensitive drum 36. Hereinafter, this point will be described in detail.

  In this embodiment, the intermediate transfer belt 31 constitutes an intermediate transfer unit 31A together with the drive roller 43, the driven roller 44, and the like, and the heater H is incorporated in the intermediate transfer unit 31A.

  The intermediate transfer unit 31A includes a synthetic resin transfer frame 81, four primary transfer rollers 41, a driving roller (first roller) 43, a driven roller (second roller) 44, and the intermediate transfer belt 31. The belt cleaner 46 and two heaters H are provided.

  Among these, the transfer frame 81 has a pair of left and right left frames 82 and 83 extending in the front-rear direction, and a connecting frame 84 that connects the left frame 82 and the right frame 83, as shown in FIG. . FIG. 7 shows a state in which the intermediate transfer belt 31 is removed for convenience of explanation as described above. The left frame 82 and the right frame 83 hold bearings (not shown) that rotatably support the four primary transfer rollers 41, the drive rollers 43, the driven rollers 44, and the like. Further, at the upper ends of the left frame 82 and the right frame 83, a container corresponding portion 85 having substantially the same shape as the bottom portion of the toner containers 47, 48, 50, 51 (see FIG. 3) is formed.

  The four primary transfer rollers 41 are arranged at equal intervals in the front-rear direction, and bearings (not shown) that rotatably support both ends of the four primary transfer rollers 41 are held by the left frame 82 and the right frame 83. . These bearings are attached to the lower end side (front end side) of a compression spring 86 (see FIG. 9) whose upper end side (base end side) is fixed to the left frame 82 and the right frame 83, and is lowered by the compression spring 86. Is being energized. Accordingly, the primary transfer roller 41 rotatably supported by a pair of left and right bearings presses the intermediate transfer belt 31 from the back surface side so that the surface of the intermediate transfer belt 31 contacts the surface of the photosensitive drum 36. Yes. Thus, a primary transfer nip T1 having an appropriate contact pressure is formed between the photosensitive drum 36 and the intermediate transfer belt 31. That is, the intermediate transfer belt 31 is sandwiched between the front and back surfaces of the photosensitive drum 36 and the surface of the primary transfer roller 41. The four primary transfer rollers 41 are magenta, cyan, yellow, and black primary transfer rollers 41 in order from the rear side (left side in FIG. 7).

  In the present embodiment, two rollers, that is, a driving roller 43 and a driven roller 44 are provided as driving system rollers for rotating the intermediate transfer belt 31. The driving roller 43 and the driven roller 44 are rotatably supported by bearings (not shown) supported by the left frame 82 and the right frame 83, respectively. The driving roller 43 is disposed in front of the primary transfer roller 41 for black, that is, among the four primary transfer rollers 41, on the most downstream side in the rotation direction of the intermediate transfer belt 31. It is disposed immediately downstream of the transfer roller 41. On the other hand, the driven roller 44 is arranged in front of the magenta primary transfer roller 41, that is, of the four primary transfer rollers 41 on the most upstream side along the rotation direction of the intermediate transfer belt 31. It is disposed immediately upstream of the primary transfer roller 41. As shown in FIG. 9, the driving roller 43 and the driven roller 44 are set to have a diameter larger than the diameter of the primary transfer roller 41, and a portion located at the lower end of each outer peripheral surface is formed. The first transfer nip T1 is located at substantially the same height. Therefore, when the intermediate transfer belt 31 is stretched between the drive roller 43 and the driven roller 44, the intermediate transfer belt 31 is positioned upstream of the drive roller 43 and downstream of the driven roller 44 along the rotational direction of the intermediate transfer belt 31. The portion (hereinafter referred to as “transfer portion side 31a”) is formed in a substantially planar shape. Of the driving roller 43 and the driven roller 44, the driving roller 43 is held so that the position of the shaft center (shaft) 43a is not displaced, whereas the driven roller 44 is rotatable at both ends. The bearing to be supported is urged rearward by an urging member 87 such as a spring, and the shaft center (shaft) 44a is moved to apply tension to the intermediate transfer belt 31. ing.

  The intermediate transfer belt 31 is stretched endlessly around the driving roller 43 and the driven roller 44. As shown in FIGS. 7 and 8, the belt width W1 of the intermediate transfer belt 31 (the dimension in the direction orthogonal to the rotation direction) is smaller than that of the drive roller 43, the driven roller 44, and the primary transfer roller 41. It is set to be longer than the length in the axial direction. The belt width W1 is set to be substantially the same as the length of the photosensitive drum 36 in the axial direction. As described above, the intermediate transfer belt 31 is stretched with an appropriate tension by the driven roller 44 being urged rearward and acting as a tension roller. The entire intermediate transfer belt 31 rotates in the arrow R31 direction as the driving roller 43 rotates in the arrow direction (see FIG. 9). At this time, the portion of the intermediate transfer belt 31 located on the transfer portion side 31a, that is, on the upstream side of the driving roller 43 and on the downstream side of the driven roller 44 is maintained in a flat state, and each image forming station. Passes between the photosensitive drums 36, 32, 33, 34, and 35 and the primary transfer roller 41. At this time, the toner images of the respective colors formed on the respective photosensitive drums 36 are sequentially primarily transferred and superimposed. These toner images are secondarily transferred onto the sheet all at once by the secondary transfer roller 45 in the secondary transfer nip T2 (see FIG. 3) as described above.

  As described above, the belt cleaner 46 is disposed in contact with the surface of the intermediate transfer belt 31 in the vicinity of the driven roller 44. The belt cleaner 46 removes toner (secondary transfer residual toner) remaining on the surface of the intermediate transfer belt 31 without being transferred to the sheet during the secondary transfer.

  In the present embodiment, the transfer frame 81, the four primary transfer rollers 41, the driving roller 43, the driven roller 44, the intermediate transfer belt 31, the belt cleaner 46, and the like constitute the intermediate transfer unit 31A. Yes. The heater H is incorporated in the intermediate transfer unit 31A.

  As shown in FIG. 5, in the present embodiment, a planar member is used as the heater member 80 constituting a part of the heater H. In the figure, two heater members 80 having the same shape are shown. The heater member 80 includes a rectangular thin plate-like insulating plate 90 that is long in the left-right direction, and a heating resistor 91 (for example, nichrome wire) disposed on the surface thereof. The heating resistor 91 is laid so as to be folded a plurality of times along the longitudinal direction of the insulating plate 80, and both ends thereof are connected to the electrodes 92.

  As shown in FIG. 6A, the heater member 80 is attached to the above-described intermediate transfer unit 31 </ b> A while being accommodated in the attachment base 93. The mounting base 93 includes a bottom portion 94 that is long in the left-right direction, and bent portions 95 and 96 that are configured to fold back the front end side and the rear end side of the bottom portion 94. The dimension of the bottom portion 94 in the front-rear direction is set slightly larger than the width dimension of the heater member 80 in the front-rear direction, and the width dimension W2 in the left-right direction of the bottom portion 94 is larger than the dimension in the left-right direction of the heater member 80. The intermediate transfer belt 31 is set to be substantially the same as the belt width W1. The mounting base 93 is made of a member having good thermal conductivity, for example, a metal plate. The heater member 80 is disposed so as to be in contact with the upper surface of the bottom 94 of the mounting base 93. Thus, the heat generated in the heating resistor 91 of the heater member 80 is transmitted to the bottom portion 94 of the mounting base 93 via the insulating plate 90 to effectively heat the bottom portion 94. The intermediate transfer belt 31 is heated by the bottom portion 94. That is, the heater member 80 and the bottom 94 constitute a heater H that substantially heats the intermediate transfer belt 31.

  In the present embodiment, the heater H is disposed so as to satisfy the following conditions.

  (1) The heater H is disposed inside the intermediate transfer belt 31. Accordingly, even if it is not possible to secure a space for arranging the heater H near the surface of the photosensitive drum 36 inside the photosensitive drum 36 or outside the photosensitive drum 36, the intermediate transfer belt 31 is moved by the heater H. By heating, the photosensitive drum 36 can be heated via the intermediate transfer belt 31.

  (2) The heater H is disposed over substantially the entire belt width W1 of the intermediate transfer belt 31. Thereby, the intermediate transfer belt 31 can be heated over almost the entire width in the belt width W1 direction. Furthermore, the intermediate transfer belt 31 can heat the photosensitive drum 36 along substantially the entire length along the axial direction thereof.

  (3) The heater H is formed in a planar shape and is disposed so as to face the back surface 31b of the intermediate transfer belt 31 in a non-contact manner. Thereby, the back surface 31b of the intermediate transfer belt 31 can be efficiently heated.

  (4) The heater H is disposed so as to face the transfer portion side 31 a of the intermediate transfer belt 31. When the intermediate transfer belt 31 is largely divided into the transfer portion side 31 a and the other portions, the transfer portion side 31 a is closer to the photosensitive drum 36. Accordingly, the heater H can heat the photosensitive drum 36 in parallel with heating the intermediate transfer belt 31.

  (5) The heater H is disposed between the transfer portion side 31a and the virtual plane S when the virtual plane S passing through the axis 43a of the driving roller 43 and the axis 44a of the driven roller 44 is considered. Has been. For example, unlike the above-described configuration, the intermediate transfer belt 31 is stretched over a driving roller 43, a driven roller 44, and a tension roller, and has a triangular shape with these three rollers as substantially apexes in a side view. May be configured. In such a case, even when the heater H is disposed so as to face the back surface 31b of the transfer portion side 31a, the heater H is disposed at a position farther from the virtual plane S than the transfer portion side 31a. Cannot effectively heat the transfer portion side 31a. Therefore, the arrangement position of the heater H is defined between the transfer portion side 31a and the virtual plane S so that the heater H can efficiently heat the back surface 31b of the transfer portion side 31a.

  (6) Of the two heaters H, one heater H is arranged between the cyan primary transfer roller 41 and the yellow primary transfer roller 41 and at an equal distance from both rollers. Set up. The other heaters H are arranged between the yellow primary transfer roller 41 and the black primary transfer roller 41 and at an equal distance from both rollers. That is, the two heaters H are located at the same distance from the two adjacent photosensitive drums 36. Thereby, both the photosensitive drums 36 can be heated uniformly by direct heating by the heater H. Although it is effective to dispose a similar heater H between the magenta primary transfer roller 41 and the cyan primary transfer roller 41, in this embodiment, this portion includes a driven member. Since the urging member 87 and the like for urging the roller 44 rearward are disposed, the heater H is not disposed for design reasons. Therefore, as described above, for example, when the tension roller is provided in addition to the drive roller 43 and the driven roller 44 and the intermediate transfer belt 31 is stretched in a triangular shape, the driven roller 44 is moved backward. Therefore, the heater H can be disposed between the primary transfer roller 41 for magenta and the primary transfer roller 41 for cyan. In contrast, in the present invention, even if there is only one heater H, a corresponding effect can be achieved.

  According to the present invention, the intermediate transfer belt 31 is heated from the back surface 31b side by the heater H provided inside the intermediate transfer belt 31, and further, the intermediate transfer belt 31 is rotated by rotating the intermediate transfer belt 31. The photosensitive drum 36 that is heated substantially uniformly over the entire length and that is in contact with the intermediate transfer belt 31 in the primary transfer nip T1 can be indirectly heated. As a result, it is possible to prevent an image flow that tends to occur in a high humidity environment.

  In the present invention, the photosensitive drum 36 is heated via the intermediate transfer belt 31. Thus, by heating the intermediate transfer belt 31, the resistance value of the intermediate transfer belt 31 is stabilized. There is also a secondary effect that the transfer is performed well.

  In the above description, the case where the intermediate transfer belt 31, the drive roller 43, the driven roller 44, and the like constitute the intermediate transfer unit 31A has been described as an example. However, the present invention is not limited to this, and the intermediate transfer belt 31 is not limited thereto. In the case where the intermediate transfer unit 31A is not configured, the same can be applied and the same effect can be obtained.

  In the above description, in the image forming apparatus having the intermediate transfer belt, the case where the heater is disposed inside the intermediate transfer belt has been described. However, the present invention is not limited to this, and the sheet is supported on the surface of the conveyance belt. The present invention can also be applied to an image forming apparatus of a type in which the sheets are sequentially conveyed to an image forming station and a plurality of toner images are transferred directly to the sheet.

FIG. 2 is a perspective view of the entire image forming apparatus as viewed from the diagonally upper left side on the front side. FIG. 2 is a perspective view of the entire image forming apparatus as viewed from the rear and obliquely upward on the left side thereof. FIG. 2 is a diagram schematically showing an internal structure of the image forming apparatus as viewed from the left side. (A), (b) is a schematic diagram explaining the closed position of a front cover and a conveyance unit, and an open position. It is the perspective view which looked at the heater from diagonally upward. (A) is the perspective view which looked at the heater of the state attached to the mounting base from diagonally upward, (b) is the perspective view which looked at the same state from diagonally downward. FIG. 3 is a perspective view of an intermediate transfer unit to which a heater is attached as viewed from below with the intermediate transfer belt removed. It is the perspective view which looked at the intermediate transfer unit with which the heater was attached from the lower part. FIG. 3 is a schematic view of a photosensitive drum, a developing device, an intermediate transfer belt, and the like viewed from the left side.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Image forming apparatus main body, 31 ... Intermediate transfer belt, 31A ... Intermediate transfer unit, 31a ... Transfer part side, 31b ... Back surface, 36 ... Photosensitive drum, 41 ... Primary transfer roller (transfer roller), 43... Drive roller (drive system roller, first roller), 43a... Axis of drive roller (axis), 44 .. driven roller (drive system roller, second roller) 44a: driven roller axis (axis), 47, 48, 50, 51: image forming station, H: heater, S: virtual plane, W1: belt width

Claims (9)

An intermediate transfer belt rotating endlessly and a plurality of image forming stations arranged along the rotation direction of the intermediate transfer belt, each of the image forming stations contacting the surface of the intermediate transfer belt An image forming apparatus in which a plurality of toner images formed on the surface of the photosensitive drum are sequentially transferred to the surface of the intermediate transfer belt;
A heater for heating the intermediate transfer belt is disposed inside the intermediate transfer belt.
An image forming apparatus. The heater is disposed over substantially the entire width in the belt width direction orthogonal to the rotation direction of the intermediate transfer belt;
The image forming apparatus according to claim 1. The heater is a planar heater disposed so as to face the back surface of the intermediate transfer belt in a non-contact manner.
The image forming apparatus according to claim 2. A plurality of drive system rollers on which the intermediate transfer belt is stretched;
Among the plurality of driving system rollers, a roller disposed on the most downstream side of the photosensitive drum on the most downstream side along the moving direction of the intermediate transfer belt is a first roller, and the photosensitive drum on the most upstream side. When the roller disposed immediately upstream is the second roller,
The heater is disposed at a position facing the back surface of the intermediate transfer belt on the transfer portion side located upstream of the first roller and downstream of the second roller.
The image forming apparatus according to claim 3. When the plane passing through the axis of the first roller and the axis of the second roller is a virtual plane, the heater is disposed between the transfer portion side of the intermediate transfer belt and the virtual plane. Yes,
The image forming apparatus according to claim 4. A plurality of transfer rollers disposed on the inner side of the intermediate transfer belt to press the back surface of the intermediate transfer belt so that the surface of the intermediate transfer belt contacts the surface of the photosensitive drum; Between the two transfer rollers adjacent to each other,
The image forming apparatus according to claim 5. The heater is disposed at an approximately equal distance from two adjacent photosensitive drums;
The image forming apparatus according to claim 6. A plurality of the heaters are disposed;
The image forming apparatus according to claim 7. The photosensitive drum is an a-Si drum;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

Images