JP2009014955A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, capable of attaining satisfactory image formation, while accurately positioning a photoreceptor unit including a plurality of photoreceptors to an image forming apparatus body without disturbance of image formation by the positioning. <P>SOLUTION: When a drum unit 21 is installed to a body casing 2 from the front side to the rear side, cutout parts 69 of the drum unit 21 abut on both ends 79 of a shaft member 78, whereby the drum unit 21 is accurately positioned. A central part 80 of the shaft member 78 is disposed above a passing path 48 so that the shortest distance L1 between the central part 80 and a transfer unit 19 is longer than the shortest distance L2 between each of the ends 79 and the transfer unit 19. Accordingly, a paper 3 passing through the passing path 48 can be prevented from interfering with the central part 80. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a color laser printer.

  A tandem type image forming apparatus is known in which photoreceptors corresponding to yellow, magenta, cyan, and black are arranged in parallel.

As such a tandem-type image forming apparatus, for example, an apparatus in which the photosensitive drums of the respective colors are integrally held on a photosensitive drum unit and the photosensitive drum unit is detachably attached to a housing has been proposed. (For example, refer to Patent Document 1).
JP 2004-13030 A

  However, in the image forming apparatus described in Patent Document 1, it is necessary to accurately position and mount the photosensitive drum unit with respect to the housing in order to prevent image formation displacement and distortion.

  On the other hand, regarding the positioning, it is necessary to arrange the positioning member so that the positioning member does not interfere with the paper during image formation.

  An object of the present invention is to achieve good image formation without hindering image formation by positioning while a photoconductor unit including a plurality of photoconductors can be accurately positioned with respect to the image forming apparatus main body. An object of the present invention is to provide an image forming apparatus capable of performing the above.

  In order to achieve the above object, according to the first aspect of the present invention, in the image forming apparatus, the image forming apparatus main body and the image forming apparatus main body can be attached to and detached from each other, and are arranged in parallel along the attaching / detaching direction. A plurality of photoconductors arranged on the downstream side of the mounting direction and positioning members provided at both ends in the rotation axis direction of the photoconductor, and arranged so as to face the plurality of photoconductors And a transfer unit for transferring the recording medium while transferring a developer image from each of the photoconductors to the recording medium, and a downstream side of the transfer unit in the transfer direction of the recording medium with respect to the transfer unit, A fixing unit for fixing the developer image transferred to the recording medium, and the recording unit to the fixing unit are arranged between the conveying unit and the fixing unit. A passage path for allowing the body to pass therethrough, and a shaft member disposed on the downstream side in the mounting direction in the image forming apparatus main body and provided along the rotation axis direction of the photosensitive member. Provided at both ends in the direction and between the both ends where the positioning members are in contact with each other, and the shortest distance to the transport unit is longer than the shortest distance between the both ends and the transport unit The center portion disposed on the photosensitive unit side with respect to the passing path is provided.

  According to a second aspect of the present invention, in the first aspect of the present invention, a longitudinal length of a central portion of the shaft member is shorter than a maximum width of a recording medium capable of forming an image in the image forming apparatus. The both end portions are provided between the fixing unit and the shaft member in the recording medium conveyance direction, and the shortest distance between the passing path is shorter than the shortest distance between the central portion and the passing path. And an opposing member that can oppose both ends of the recording medium.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the longitudinal length of the central portion of the shaft member is longer than the minimum width of a recording medium capable of image formation in the image forming apparatus. It is characterized by that.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the shaft member connects the both end portions and the central portion, and intersects the longitudinal direction of the central portion. It is characterized by having a relay part extending in the direction to be.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to third aspects, the shaft member has a flat surface formed flat along the longitudinal direction, and a cross-section continuous with the flat surface. And an arc surface formed in an arc shape.

  According to the first aspect of the present invention, when the photosensitive unit is mounted on the image forming apparatus main body from the upstream side to the downstream side in the mounting direction, the positioning member of the photosensitive unit is The photosensitive member unit is accurately positioned with respect to the image forming apparatus main body by contacting both end portions of the shaft member.

  Also, the shaft member is in contact with the positioning member at both ends thereof, while the central portion thereof is such that the shortest distance between the central portion and the transport unit is longer than the shortest distance between both ends and the transport unit. It is arranged on the photosensitive unit side with respect to the passing path. Therefore, when the recording medium on which the developer image is transferred in the transport unit is transported from the transport unit to the fixing unit, it is possible to prevent the recording medium passing through the passage path from interfering with the central portion. it can.

  According to the second aspect of the present invention, the longitudinal length of the central portion of the shaft member is shorter than the maximum width of the recording medium capable of image formation in the image forming apparatus. A long length can be secured. Therefore, the positioning accuracy can be improved.

  On the other hand, when the recording medium having the maximum width is conveyed, the opposing members arranged to face both ends interfere with both ends of the recording medium before the recording medium interferes with the central portion. Therefore, it is possible to reliably prevent interference with the central portion of the recording medium having the maximum width.

  According to the third aspect of the present invention, the longitudinal length of the central portion of the shaft member is longer than the minimum width of the recording medium on which image formation is possible in the image forming apparatus. Therefore, interference between the recording medium having the minimum width and the central portion can be surely prevented.

  According to the fourth aspect of the present invention, the shaft member includes the both end portions, the central portion, and the relay portion that connects them and extends in the direction intersecting the longitudinal direction of the central portion. Therefore, the shaft member can be formed easily and accurately.

  According to the invention described in claim 5, the shaft member includes a flat surface formed flat along the longitudinal direction, and an arc surface formed in a cross-sectional arc shape continuously with the flat surface. . Therefore, the shaft member can be formed easily and accurately.

1. Overall Configuration of Color Laser Printer FIG. 1 is a cross-sectional side view of an essential part showing an embodiment of a color laser printer as an example of an image forming apparatus of the present invention.

The color laser printer 1 is a horizontal tandem color laser printer in which a plurality of photosensitive drums 24 to be described later are arranged in parallel in the horizontal direction. The color laser printer 1 forms an image on a fed sheet 3 and a sheet feeding unit 4 for feeding a sheet 3 as an example of a recording medium in a body casing 2 as an example of an image forming apparatus body. An image forming unit 5 for discharging the image, and a paper discharge unit 6 for discharging the paper 3 on which the image is formed.
(1) Main Body Casing The main body casing 2 is formed in a box shape having a substantially rectangular shape in side view. A drum housing space 15 for housing a drum unit 21 (not shown) is defined in the main body casing 2.

  A front cover 16 is provided on one side surface (front surface) of the main casing 2. The front cover 16 tilts forward of the main body casing 2 to open the drum housing space 15, and rises along the front surface of the main body casing 2 to close the drum housing space 15. When the drum housing space 15 is opened, the drum unit 21 can be attached to and detached from the drum housing space 15.

In the following description, one side (left side in FIG. 1) where the front cover 16 is provided is referred to as a front side, and the opposite side (right side in FIG. 1) is referred to as a rear side. Further, the left and right sides are defined with reference to the color laser printer 1 as viewed from the front side. Further, regarding the drum unit 21 and the developing cartridge 22, the front / rear / left / right / upper / lower directions are defined based on the state where the drum unit 21 and the developing cartridge 22 are mounted on the main casing 2, unless otherwise specified.
(2) Paper Feed Unit The paper feed unit 4 includes a paper feed tray 7 that is detachably attached to the bottom of the main body casing 2. A paper feed roller 10 is disposed above the front end of the paper feed tray 7. Further, the paper feed unit 4 includes a substantially U-shaped paper feed path 11 formed between the front end of the paper feed tray 7 and a conveyance belt 43 described later. On the paper feed path 11, a separation roller 8, a separation pad 9, a paper dust removing roller 12, a pinch roller 13 and a pair of registration rollers 14 are provided.

The sheet 3 stacked on the sheet feed tray 7 is fed to the sheet feed path 11 by the rotation of the sheet feed roller 10. Thereafter, the sheets 3 are separated one by one between the separation roller 8 and the separation pad 9. Thereafter, the paper 3 passes between the paper dust removing roller 12 and the pinch roller 13, the paper dust is removed by the paper dust removing roller 12, and then conveyed to the registration roller 14. The registration roller 14 sends out the paper 3 onto a conveyance belt 43 described later after registration.
(3) Image Forming Unit The image forming unit 5 includes a scanner unit 17, a process unit 18, a transfer unit 19 as a transport unit, and a fixing unit 20.
(3-1) Scanner Unit The scanner unit 17 is disposed on the upper part of the main body casing 2. In the scanner unit 17, for example, optical members such as four light sources, a polygon mirror, an fθ lens, a reflecting mirror, and a surface tilt correction lens are provided. A laser beam based on image data emitted from each light source is deflected and scanned by a polygon mirror, passes through an fθ lens and a surface tilt correction lens, and is reflected by a reflecting mirror. Irradiated on the surface of 24 by high-speed scanning.
(3-2) Process Unit The process unit 18 is disposed below the scanner unit 17 and above the paper feed unit 4, and includes a drum unit 21 as one photoconductor unit and four units corresponding to each color. And a developing cartridge 22.
(3-2-1) Drum Unit The drum unit 21 is detachably attached to the drum housing space 15 along the front-rear direction.

  The drum unit 21 includes four drum subunits 23 corresponding to the respective colors. That is, the drum subunit 23 includes a yellow drum subunit 23Y, a magenta drum subunit 23M, a cyan drum subunit 23C, and a black drum subunit 23K. These are arranged in parallel in the above-described order from the front side to the rear side along the front-rear direction (detachment direction).

Each drum subunit 23 includes a photosensitive drum 24 as an example of a photosensitive member, a scorotron charger 25, and a cleaning brush 26. The photosensitive drum 24 is disposed along the left-right direction (width direction), and is supported by the drum subunit 23 so as to be rotatable about its central axis. The scorotron charger 25 is supported by the drum subunit 23 so as to be opposed to the photosensitive drum 24 with an interval in the upper oblique rear side of the photosensitive drum 24. The cleaning brush 26 is supported by the drum subunit 23 so as to face and contact the photosensitive drum 24 behind the photosensitive drum 24.
(3-2-2) Developing Cartridge The developing cartridge 22 is detachably provided corresponding to the drum subunit 23 corresponding to each color.

  That is, a yellow developing cartridge 22Y is provided corresponding to the yellow drum subunit 23Y. A magenta developing cartridge 22M is provided corresponding to the magenta drum subunit 23M. A cyan developing cartridge 22C is provided corresponding to the cyan drum subunit 23C. A black developing cartridge 22K is provided corresponding to the black drum subunit 23K.

Each developing cartridge 22 includes a developing frame 31. In the upper part of the developing frame 31, toner as an example of a developer is accommodated, and an agitator 32 is provided. Under the developing frame 31, a supply roller 33, a developing roller 34, and a layer thickness regulating blade 35 are provided.
(3-2-3) Developing Operation in Process Unit In each developing cartridge 22, the toner accommodated in the developing frame 31 is supplied to the supply roller 33 while being stirred by the agitator 32, and the supply roller 33 is further supplied. Is supplied to the developing roller 34. At this time, it is triboelectrically charged between the supply roller 33 and the developing roller 34 to which a developing bias is applied.

  Thereafter, as the developing roller 34 rotates, excess toner is scraped off from the developing roller 34 by the layer thickness regulating blade 35 and is carried on the surface of the developing roller 34 as a thin layer having a constant thickness.

  On the other hand, in each drum subunit 23, the surface of the photosensitive drum 24 is uniformly positively charged by corona discharge of the scorotron charger 25. The surface of the positively charged photosensitive drum 24 is irradiated with a laser beam from the scanner unit 17, whereby an electrostatic latent image corresponding to an image to be formed on the paper 3 is formed.

When the electrostatic latent image formed on the surface of the photosensitive drum 24 is opposed to the developing roller 34 by the rotation of the photosensitive drum 24, the toner carried on the developing roller 34 becomes the electrostatic latent image (that is, uniform). Of the surface of the photosensitive drum 24 that is positively charged to the surface of the photosensitive drum 24 that is exposed to a laser beam and has a lowered potential. As a result, the electrostatic latent image is visualized and a toner image is carried on the surface of the photosensitive drum 24.
(3-3) Transfer Unit The transfer unit 19 extends in the front-rear direction so as to face all the photosensitive drums 24 in the main body casing 2 above the paper feed unit 4 and below the process unit 18. Are arranged. The transfer unit 19 includes a drive roller 41, a driven roller 42, a conveyance belt 43, and a transfer roller 44.

  The drive roller 41 is disposed at the rear end of the transfer unit 19, specifically, behind the black drum subunit 23K. The driven roller 42 is disposed in front of the front end of the transfer unit 19, specifically, the yellow drum subunit 23Y. The driving roller 41 and the driven roller 42 are disposed to face each other with a space in the front-rear direction.

  The conveyor belt 43 is an endless belt and is wound between the driving roller 41 and the driven roller 42.

  At the time of image formation, when the driving roller 41 is rotated, the driven roller 42 is driven, and the conveying belt 43 is located between the driving roller 41 and the driven roller 42 at a transfer position where it contacts the respective photosensitive drums 24. Then, it rotates so as to rotate in the same direction as the photosensitive drum 24.

  The transfer roller 44 is disposed so as to be opposed to each other with the photosensitive drum 24 and the conveyor belt 43 interposed therebetween in the wound conveyor belt 43. Each transfer roller 44 follows the same direction as the circumferential movement direction of the transport belt 43 at the transfer position.

  The sheet 3 fed from the sheet feeding unit 4 is transported from the front side to the rear side along the front-rear direction by the transport belt 43 and sequentially passes through the transfer position corresponding to each photosensitive drum 24. When the sheet 3 passes through each transfer position, the toner image on the photosensitive drum 24 is transferred to the sheet 3 by the transfer bias applied to the transfer roller 44. Thus, the toner image is transferred from each photosensitive drum 24 while the sheet 3 is conveyed from the front side to the rear side, and a color image is formed.

Note that paper dust from the paper 3 adhering to the photosensitive drum 24 after the transfer is collected by the cleaning brush 26.
(3-4) Fixing Unit The fixing unit 20 is arranged at a distance from the fixing unit 20 on the downstream side in the transport direction of the sheet 3 with respect to the transfer unit 19, specifically, behind the transfer unit 19. . The fixing unit 20 includes a heating roller 46 and a pressure roller 47 that presses the heating roller 46.

  The heating roller 46 is disposed along the width direction, and is supported by the main body casing 2 so as to be rotatable around its central axis. The pressure roller 47 is disposed below the heating roller 46 so as to face the heating roller 46 along the width direction, and is supported so as to be rotatable around its central axis. The pressure roller 47 presses the heating roller 46 from below.

  A pressure contact portion (nip portion) between the heating roller 46 and the pressure roller 47 is substantially opposed to the uppermost portion of the drive roller 41 in the front-rear direction.

  The fixing unit 20 is provided with a fixing casing 45 that covers the heating roller 46 (see FIG. 3). The fixing casing 45 is disposed above the heating roller 46 and is provided so as to cover the upper half portion of the heating roller 46.

  Further, a passage path 48 for allowing the sheet 3 to pass from the transfer unit 19 to the fixing unit 20 is formed between the transfer unit 19 and the fixing unit 20. The passage path 48 is a path for conveying the paper 3 that is separated from the driving roller 41 toward the pressure contact portion of the pressure roller 47 and the heating roller 46, specifically, the uppermost portion of the driving roller 41 and The pressure roller 47 and the heating roller 46 are formed along a straight line connecting the pressure contact portions (nip portions). The passage path 48 is formed substantially horizontally along the front-rear direction. The passage path 48 is provided with a guide member 49 for guiding and conveying the paper 3. The upper surface of the guide member 49 is disposed along the passage path 48.

Then, the sheet 3 on which the color image is formed in the transfer unit 19 passes through the passage path 48 and is conveyed to the fixing unit 20. In the fixing unit 20, the color image is thermally fixed to the paper 3 while the paper 3 passes between the heating roller 46 and the pressure roller 47.
(4) Paper Discharge Unit The paper discharge unit 6 includes a substantially C-shaped paper discharge path 51 that opens forward. On the paper discharge path 51, a conveyance roller 52, a pinch roller 53, and a pair of paper discharge rollers 54 are provided.

The sheet 3 conveyed from the fixing unit 20 is conveyed along a sheet discharge path 51 by a conveyance roller 52 and a pinch roller 53, and is discharged onto a sheet discharge tray 55 formed on the upper surface of the main casing 2 by the sheet discharge roller 54. The paper is ejected.
2. 2 is a perspective view of the drum unit, FIG. 3 is a perspective view of the main part in the main body casing (when the drum unit is not mounted), and FIG. 4 is a perspective view of the main part in the main body casing (drum unit). FIG. 5 is a front view of the main casing, and FIG. 6 is an enlarged side sectional view of the vicinity of the fixing unit in the main casing. Hereinafter, with reference to FIG. 1 thru | or FIG. 6, the structure regarding the positioning with respect to the main body casing 2 of the drum unit 21 is explained in full detail.
(1) Drum Unit As shown in FIG. 2, the drum unit 21 includes four drum subunits 23 arranged in parallel in the front-rear direction, a front beam 61 arranged in front of the frontmost drum subunit 23, and A rear beam 62 disposed behind the rearmost drum subunit 23 and a pair of side plates 63 sandwiching them from both sides in the width direction are provided.

  In the drum unit 21, the four drum subunits 23, the front beam 61, the rear beam 62, and the pair of side plates 63 are detachably attached to the drum housing space 15 of the main body casing 2 as one member.

  A corresponding developing cartridge 22 is detachably attached to each drum subunit 23.

  The front beam 61 is installed between the pair of side plates 63 in front of the drum subunit 23 at the foremost end. The front beam 61 is provided with a near-side grip portion 64 having a substantially U shape in a plan view and rotatably supported by the front beam 61 at the center in the width direction.

  The rear beam 62 is installed between the pair of side plates 63 behind the rearmost drum subunit 23. The rear beam 62 is provided with a rear-side grip portion 65 that is supported by the rear beam 62 and is substantially U-shaped in rear view.

  The side plates 63 are provided as a pair so as to sandwich the front beam 61, the four drum subunits 23, and the rear beam 62 from both sides in the width direction. Each side plate 63 extends in the front-rear direction, is formed in a substantially elongated rectangular plate shape in a side view, and is fixed to them.

  The upper edge of each side plate 63 is formed in a straight line along the front-rear direction (horizontal direction), and is formed with a flange 66 that is bent outward in the width direction so as to have an L-shaped cross section.

  A protruding portion 68 that protrudes rearward is formed on the rear end portion (downstream end portion in the mounting direction) of each side plate 63, and a positioning member that clamps a shaft member 78 (described later) in the vertical direction on the lower side. As an example, a notch 69 is formed.

  The notch 69 is formed in a substantially concave shape with the rear open at the lower portion of the rear edge. Specifically, among the upper and lower end edges sandwiching the shaft member 78 of the notch portion 69, the upper end edge 70 is formed in a straight line along the front-rear direction (horizontal direction) from the rear end edge to the front deepest portion. Has been. Further, the lower end edge 71 is formed on a straight line that inclines with a constant gradient from the lower rear side to the upper front side from the rear end edge to the deepest part in the front. Further, the deepest edge 72 of the notch 69 is formed in a straight line along the vertical direction (vertical direction) so as to connect the upper edge 70 and the lower edge 71. The connecting portion between the upper edge 70 and the deepest edge 72 is formed in a curved shape, and the connecting portion between the lower edge 71 and the deepest edge 72 is formed in a curved shape.

A roller member 73 is provided at the rear end of each side plate 63.
(2) Main Body Casing As shown in FIG. 3, the main body casing 2 includes a pair of side frames 76 (see FIG. 5) that are opposed to each other with an interval in the width direction.

  The transfer unit 19 and the fixing unit 20 are supported by the main casing 2 by fixing both ends in the width direction to the pair of side frames 76.

  A guide rail 77 is formed on each side frame 76 in a straight line along the front-rear direction so as to face the flange portion 66 of the drum unit 21.

  A shaft member 78 with which each notch portion 69 of the drum unit 21 abuts is provided at the rear end portion (downstream end portion in the mounting direction) of the main casing 2.

  As shown in FIG. 1, the shaft member 78 is disposed between the transfer unit 19 and the fixing unit 20 and above the passage path 48 (on the drum unit 21 side), and a pair of side frames 76. In between, it is constructed along the width direction (direction parallel to the rotation axis direction of the photosensitive drum 24), and is fixed to each side frame 76.

  The shaft member 78 has a round shaft shape, and as shown in FIG. 3, the shaft member 78 is formed in a crank shape that is recessed in the middle of the width direction upward and slightly rearward. Specifically, as shown in FIGS. 4 and 5, the shaft member 78 includes both end portions 79, a central portion 80 disposed between the both end portions 79, and a relay connecting the both end portions 79 and the central portion 80. The unit 81 is integrally provided.

  Both end portions 79 are arranged at both ends in the longitudinal direction (width direction) of the shaft member 78, and the respective notch portions 69 are in contact with each other as will be described later. Each end 79 extends along the width direction and is disposed at the same position in a side view (when projected in the width direction, the same applies hereinafter) (see FIG. 1).

  The central portion 80 extends along the width direction, and is disposed slightly above and behind the both end portions 79 in a side view. Accordingly, as shown in FIG. 6, in the side view, the shortest distance L1 between the central portion 80 and the transfer unit 19 (drive roller 41) is the same as the both ends 79 and the transfer unit 19 (drive roller 41). It arrange | positions so that it may become longer than the shortest distance L2.

  Further, as shown in FIG. 5, the length in the longitudinal direction of the central portion 80 is larger than the paper width (maximum width) W1 of the paper 3 of the maximum size (for example, A4 size) that can be image-formed by the color laser printer 1. It is short and is longer than the paper width (minimum width) W2 of the paper 3 of the minimum size (for example, B5 size) that can be imaged by the color laser printer 1.

  The relay portion 81 is disposed between the inner end in the width direction of each end portion 79 and both ends in the width direction of the central portion 80, and connects each end portion 79 and the central portion 80. Thus, the both end portions 79 and the central portion 80 are integrally formed so as to be continuous via the relay portion 81.

  As shown in FIG. 6, the relay portion 81 is obliquely inclined from the inner end in the width direction of both end portions 79 in a direction intersecting the longitudinal direction of both end portions 79, specifically, slightly upward toward the rear side. In addition, as shown in FIG. 5, when viewed from the front (when projected in the front-rear direction, the same applies hereinafter), it extends obliquely from both ends 79 toward the inside in the width direction, and extends to both ends in the width direction of the central portion 80. It is connected. As a result, the shaft member 78 is arranged such that the central portion 80 is slightly rearward from the both end portions 79. In addition, the connection part of the relay part 81 and the both ends 79 and the connection part of the relay part 81 and the center part 80 are formed in the curved shape.

  As shown in FIG. 1, the shaft member 78 faces the sheet 3 passing through the passage path 48 in the vertical direction. For example, when a sheet 3 of the maximum size (for example, A4 size) that can form an image passes through the passage path 48, as shown in FIG. opposite. Further, the image forming area of the sheet 3 and the central portion 80 face each other. Further, for example, when a paper 3 of a minimum size (for example, B5 size) capable of image formation passes through the passage path 48, the paper 3 and the central portion 80 face each other. Further, the image forming area of the sheet 3 and the central portion 80 face each other.

  Further, as shown in FIGS. 3 and 5, a holding member as an example of a facing member disposed opposite to both end portions 79 of the shaft member 78 is provided at the rear end portion (downstream side end portion in the mounting direction) of the main casing 2. 82 is provided.

  The pressing member 82 is supported on the front wall of the fixing casing 45. As shown in FIG. 5, the lower end portion of the pressing member 82 is disposed below the inner end in the width direction of each end portion 79 and below the relay portion 81 that is continuous with the end portion 79 so as to face them in the vertical direction. The main body casing 2 is provided on both sides in the width direction.

  Each pressing member 82 is formed in a substantially triangular shape in a front view in which a lower end portion of the pressing member 82 is inclined upward from the outer side in the width direction toward the inner side in the width direction. Further, as shown in FIG. 6, each pressing member 82 is formed in a substantially triangular shape when viewed from the side, and is disposed between the fixing unit 20 and the shaft member 78 in the front-rear direction when viewed from the side.

  Specifically, the pressing member 82 is disposed behind the shaft member 78, and in a side view, the shaft is arranged such that the lower end portion of the pressing member 82 is closer to the passage path 48 (guide member 49) than the both end portions 79. It is arranged below the member 78. Accordingly, the pressing member 82 is configured such that the shortest distance L3 between the pressing member 82 and the passing path 48 (guide member 49) is shorter than the shortest distance L4 between the central portion 80 and the passing path 48 (guide member 49). Is arranged.

Further, as shown in FIG. 5, each pressing member 82 is disposed on the outer side in the width direction with respect to both edges in the width direction of the sheet 3 having a minimum size (for example, B5 size) capable of forming an image. In addition, the inner end in the width direction of each pressing member 82 is outside the image forming area of the maximum size (for example, A4 size) of the sheet 3 of image forming and the end of the sheet 3 in the width direction. It is arrange | positioned inside the width direction rather than the edge. Accordingly, each pressing member 82 is disposed so as to be opposed to both ends in the width direction of the maximum size (for example, A4 size) paper 3 capable of forming an image.
4). Mounting of Drum Unit to Body Casing To mount the drum unit 21 to the body casing 2, first, as shown in FIG. 1, the front cover 16 is tilted forward to open the drum housing space 15. Then, the front side gripping part 64 and the back side gripping part 65 of the drum unit 21 shown in FIG. 2 are respectively gripped by both hands, and the drum unit 21 is moved from the front side to the rear side in the front-rear direction (horizontal direction) into the drum housing space 15. Install toward the side. Specifically, one hand holding the back side gripping part 65 is released and the drum unit 21 is pushed forward with the other hand holding the front side gripping part 64.

  Then, the roller members 73 of the drum unit 21 are guided by the guide rails 77 shown in FIG. 3 until the respective notches 69 of the drum unit 21 come into contact with both end portions 79 of the shaft member 78, and the flanges 66 are moved relative to the guide rails 77. The drum unit 21 slides forward while sliding.

  As shown in FIG. 4, the drum unit 21 is positioned in the main casing 2 when each notch 69 abuts against both end portions 79. At this time, the both end portions 79 are guided to the deepest edge 72 along the lower end 71 of each notch 69 and are fitted to the deepest edge 72. Further, the upper end edge 70 restricts upward movement of the both end portions 79.

  Thereafter, the other hand holding the front side gripping portion 64 is released, the front cover 16 is raised along the front surface of the main casing 2, and the drum housing space 15 is closed. As a result, the drum unit 21 is mounted on the main casing 2.

The front cover 16 is tilted forward to open the drum housing space 15, and then, when the front gripping portion 64 is gripped and the drum unit 21 is pulled out rearward, the drum unit 21 is detached from the main casing 2. be able to.
5). Image Forming Operation During image formation, the shaft 3 is opposed to the unfixed sheet 3 passing through the passage path 48 in the vertical direction. Then, when the central portion 80 facing the image forming area of the paper 3 and the paper 3 before fixing are in contact with each other, the toner on the paper 3 adheres to the central portion 80 and is formed on the paper 3 as a result. The image is disturbed and the central portion 80 is contaminated with toner.

However, in the color laser printer 1, the occurrence of the above problems is prevented as follows according to the size of the paper 3.
(1) In the case of the maximum size paper that can form an image In other words, when forming the maximum size image forming paper (for example, A4 size) 3, the paper 3 on which the color image is transferred by the transfer unit 19 Is conveyed to the fixing unit 20 through the passage path 48, as shown in FIG. 6A, the middle portion of the sheet 3 in the conveyance direction is between the heating roller 46 and the pressure roller 47. On the other hand, when the downstream end of the sheet 3 in the transport direction is separated from the transfer unit 19, the downstream end of the sheet 3 in the transport direction tends to float upward.

  Then, the pressing members 82 provided on both sides in the width direction of the main body casing 2 come into contact with both ends in the width direction of the paper 3, and further lifting at both ends in the width direction of the paper 3 is restricted. As a result, contact with both end portions 79 at both ends in the width direction of the sheet 3 is prevented.

  At this time, the lifting at both ends in the width direction of the sheet 3 is restricted by the pressing members 82, while the center in the width direction of the sheet 3 is at the top along the width direction as indicated by a chain line. It floats in a bow shape.

However, the central portion 80 of the shaft member 78 is disposed slightly above and behind the both end portions 79 in a side view so as to escape from the floating sheet 3. Therefore, even if the center in the width direction of the sheet 3 is raised in an arcuate shape, contact with the central portion 80 at the center in the width direction of the sheet 3 is prevented.
(2) In the case of the minimum size paper capable of image formation When forming the minimum size paper (for example, B5 size) paper 3 capable of image formation, the paper 3 on which the color image is transferred in the transfer unit 19 Is conveyed to the fixing unit 20 through the passage path 48, as shown in FIG. 6B, the middle portion of the sheet 3 in the conveyance direction is between the heating roller 46 and the pressure roller 47. On the other hand, when the downstream end portion in the transport direction of the paper 3 is separated from the transfer unit 19, the downstream end portion in the transport direction of the paper 3 is lifted upward.

  At this time, since each pressing member 82 is arranged on both outer sides in the width direction than the sheet 3, both ends in the width direction of the sheet 3 do not contact with each pressing member 82, and the downstream end in the transport direction of the sheet 3. The part floats up in all width directions.

However, the central portion 80 of the shaft member 78 is disposed slightly above and behind the both end portions 79 in a side view so as to escape from the floating sheet 3. Moreover, the central portion 80 is formed longer than the paper width (minimum width) W2 of the paper 3 (see FIG. 5). For this reason, even if the sheet 3 is lifted in all width directions, the contact of the sheet 3 with the central portion 80 is prevented.
6). Advantages of the embodiment (1) As described above, according to the color laser printer 1, if the drum unit 21 is attached to the main body casing 2 along the front-rear direction from the front side to the rear side, the drum unit Each notch 69 of 21 contacts the both ends 79 of the shaft member 78, and the drum unit 21 is positioned with respect to the main body casing 2 with high accuracy.

The shaft member 78 is in contact with the notches 69 at both end portions 79, while the center portion 80 has a shortest distance L 1 between the center portion 80 and the transfer unit 19 between the end portions 79 and the transfer unit 19. It is arranged above the passage path 48 so as to be longer than the shortest distance L2. Therefore, when the sheet 3 on which the color image is transferred in the transfer unit 19 is conveyed from the transfer unit 19 to the fixing unit 20, the sheet 3 passing through the passage path 48 and the central portion 80 interfere with each other. Can be prevented. As a result, it is possible to prevent disturbance of the image on the sheet 3 and contamination of the center part 80 due to toner due to contact between the center part 80 and the sheet 3 before fixing.
(2) Further, in the shaft member 78, the length in the longitudinal direction of the central portion 80 is formed to be shorter than the sheet width (maximum width) W1 of the sheet 3 having the maximum size (for example, A4 size) capable of image formation. Therefore, the length in the longitudinal direction of both end portions 79 can be secured long. Therefore, the positioning accuracy can be improved.

On the other hand, when the maximum size paper 3 capable of forming an image is conveyed, the pressing members 82 arranged opposite to the both ends 79 are arranged at both ends in the width direction of the paper 3 before the paper 3 interferes with the central portion 80. Interfere with. Therefore, it is possible to reliably prevent interference with the central portion 80 of the maximum size paper 3 that can form an image.
(3) On the other hand, in the shaft member 78, the length in the longitudinal direction of the central portion 80 is longer than the paper width (minimum width) W2 of the paper 3 of the minimum size (for example, B5 size) capable of image formation. . Therefore, it is possible to reliably prevent interference between the minimum size paper 3 capable of forming an image and the central portion 80.
(4) Further, the shaft member 78 is integrally provided with both end portions 79, a central portion 80 and a relay portion 81. Therefore, the shaft member 78 can be formed easily and accurately.
7). Other Embodiments (1) In the above description, the shaft member 78 is integrally formed so that both end portions 79 and the central portion 80 are continuous via the relay portion 81. However, for example, both end portions 79, the central portion 80, and the relay portion 81 can be prepared as separate members, and the both end portions 79 and the central portion 80 can be connected by the relay portion 81 as a separate member. In this case, for example, the relay portion 81 is formed in an oval shape or a rectangular shape, and two holes that pass through the end portions 79 and the central portion 80 are formed side by side in the relay portion 81. A shaft member 78 is formed by inserting the end portion 79 and the central portion 80 respectively.
(2) In the above description, the central portion 80 of the shaft member 78 is disposed slightly above the rear end 79 with respect to the end portions 79 in a side view. For example, as shown in FIG. The central portion 80 can be arranged at the same position with respect to both end portions 79 in a side view and can be formed in a substantially D-shaped cross section. In FIG. 7, the same members as those described above are denoted by the same reference numerals, and the description thereof is omitted.

  That is, in FIG. 7, the shaft member 78 has both end portions 79 and a central portion 80 formed in a straight line along the width direction, and both end portions 79 are formed from round shafts in the same manner as described above, and the center portion 80 has a substantially D-shaped cross section. The central portion 80 includes a flat surface 83 and a circular arc surface 84 continuous from the flat surface 83 on the outer peripheral surface. The flat surface 83 is formed below the shaft member 78, and is formed flat along the longitudinal direction. The arc surface 84 is formed in a circular arc shape continuously from both end edges of the flat surface 83.

  In the embodiment shown in FIG. 7, when the paper 3 passes through the passage path 48 and is transported to the fixing unit 20, an intermediate portion in the transport direction of the paper 3 is sandwiched between the heating roller 46 and the pressure roller 47. Even if the downstream end of the sheet 3 in the transport direction is separated from the transfer unit 19 and the downstream end of the sheet 3 in the transport direction is lifted upward, the central portion 80 can escape from the lifted sheet 3. A flat surface 83 that is notched is formed.

  Therefore, as shown in FIG. 7A, when a sheet 3 having the maximum size (for example, A4 size) capable of forming an image is conveyed, the lifting of both ends in the width direction of the sheet 3 is restricted by the pressing member 82. On the other hand, even if the center in the width direction of the paper 3 is raised like an arc as indicated by a chain line, it is possible to prevent the paper 3 from coming into contact with the central portion 80 in the center in the width direction.

  Further, as shown in FIG. 7B, when a paper 3 having a minimum size (for example, B5 size) capable of forming an image is conveyed, even if the paper 3 floats up in all the width directions, the paper 3 Can be prevented from contacting the central portion 80.

  In the shaft member 78 shown in FIG. 7, the central portion 80 may be cut and formed into a substantially D-shaped cross section, and bending is not required. Therefore, the shaft member 78 is formed easily and accurately. Can do.

1 is a side sectional view of an essential part showing an embodiment of a color laser printer as an example of an image forming apparatus of the present invention. It is a perspective view of a drum unit. It is a principal part perspective view in a main body casing (drum unit unmounted state). It is a principal part perspective view in a main body casing (drum unit mounting state). It is a front view of a main body casing. FIGS. 4A and 4B are enlarged side sectional views in the vicinity of a fixing unit in a main body casing, where FIG. 5A shows a conveyance state of a maximum size paper that can form an image, and FIG. Indicates. FIGS. 7A and 7B are enlarged side sectional views corresponding to FIG. 6 of another embodiment, in which FIG. 6A shows a conveyance state of a maximum size paper that can form an image, and FIG. The conveyance state of is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color laser printer 2 Main body casing 3 Paper 19 Transfer unit 20 Fixing unit 21 Drum unit 24 Photosensitive drum 48 Passing path 69 Notch part 78 Shaft member 79 Both ends 80 Center part 81 Relay part 82 Holding member 83 Flat surface 84 Arc surface

Claims (5)

An image forming apparatus main body;
A plurality of photoconductors that are detachable from the image forming apparatus main body and are arranged in parallel along the direction of attachment and detachment, and are arranged on the downstream side of the mounting direction, at both ends of the rotation axis of the photoconductor. A photoconductor unit comprising a positioning member provided;
A transport unit disposed so as to face the plurality of photoconductors, and transporting the recording medium while transferring a developer image from each of the photoconductors to the recording medium;
A fixing unit disposed on the downstream side in the conveyance direction of the recording medium with respect to the conveyance unit, and for fixing the developer image transferred to the recording medium;
A passage path disposed between the transport unit and the fixing unit, for passing a recording medium from the transport unit to the fixing unit;
A shaft member disposed on the downstream side of the mounting direction in the image forming apparatus main body and provided along the rotational axis direction of the photoconductor,
The shaft member is
Both end portions provided at both ends in the longitudinal direction, with which the positioning members are in contact;
It is provided between the both ends, and is arranged on the photosensitive unit side with respect to the passing path so that the shortest distance between the both ends and the transport unit is longer than the shortest distance between the both ends and the transport unit. An image forming apparatus comprising: a central portion. The longitudinal length of the central portion of the shaft member is shorter than the maximum width of a recording medium capable of image formation in the image forming apparatus,
The both ends are provided between the fixing unit and the shaft member in the conveyance direction of the recording medium, and the shortest distance between the passing path is shorter than the shortest distance between the central portion and the passing path. The image forming apparatus according to claim 1, further comprising a facing member that is disposed so as to face the recording medium and that can face both ends of the recording medium.   3. The image forming apparatus according to claim 1, wherein a length in a longitudinal direction of a central portion of the shaft member is longer than a minimum width of a recording medium capable of forming an image in the image forming apparatus.   The shaft member includes a relay portion that connects the both end portions and the central portion and extends in a direction intersecting with a longitudinal direction of the central portion. An image forming apparatus according to claim 1.   The said shaft member is provided with the flat surface formed flat along a longitudinal direction, and the circular arc surface formed in the cross-sectional arc shape continuously on the flat surface, The 1st thru | or characterized by the above-mentioned. The image forming apparatus according to claim 3.

Images