Tandem photosensitive-member unit having grip part Number:7,426,355 from the United States Patent and Trademark Office (PTO) owispatent

Title: Tandem photosensitive-member unit having grip part

Abstract: An image-forming device includes a main body and a tandem photosensitive-member unit. The tandem photosensitive-member unit includes a unit frame, a plurality of photosensitive members, a front-side grip part, and a rear-side grip. The unit frame is configured to be slidably installed to and removed from the main body in a predetermined direction. The unit frame has a leading side and a trailing side with respect to the predetermined direction. The plurality of photosensitive members is provided corresponding to a plurality of colors and is supported by the unit frame. The front-side grip part is provided at the leading side of the unit frame. The rear-side grip part is provided at the trailing side of the unit frame.

Patent Number: 7,426,355 Issued on 09/16/2008 to Okabe

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Inventors:	Okabe; Yasushi (Nagoya, JP)
Assignee:	Brother Kogyo Kabushiki Kaisha (Nagoya-shi, Aichi-ken, JP)
Appl. No.:	11/502,388
Filed:	August 11, 2006

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Foreign Application Priority Data

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Aug 12, 2005 [JP]			2005-234824
Dec 27, 2005 [JP]			2005-376111

Current U.S. Class:	399/111 ; 399/112; 399/92
Current International Class:	G03G 21/18 (20060101); G03G 15/01 (20060101)
Field of Search:	399/111,112,113,110,299,92

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References Cited [Referenced By]

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U.S. Patent Documents

5107304	April 1992	Haneda et al.
5282012	January 1994	Terada et al.
5327208	July 1994	Matsuo et al.
5812910	September 1998	Kim
5963759	October 1999	Kojima et al.
6041203	March 2000	Suzuki et al.
6738590	May 2004	Okimura et al.
6978103	December 2005	Miura et al.
7072602	July 2006	Hatori et al.
2001/0055500	December 2001	Katakabe et al.
2003/0053819	March 2003	Nomura et al.
2004/0101328	May 2004	Kimura et al.
2005/0147432	July 2005	Miura et al
2007/0009282	January 2007	Sato et al.

Foreign Patent Documents

	59-033461		Feb., 1984		JP
	03-180861		Aug., 1991		JP
	08-220819		Aug., 1996		JP
	2003-050531		Feb., 2003		JP
	2003-287992		Oct., 2003		JP
	2003-316105		Nov., 2003		JP
	2004-109886		Apr., 2004		JP

Primary Examiner: Chen; Sophia S
Attorney, Agent or Firm: Banner & Witcoff, Ltd

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Claims

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What is claimed is:

1. An image-forming device comprising: a main body; and a tandem photosensitive-member unit including: a unit frame configured to be slidably installed to the main body in a predetermined direction and removed from the main body in a reverse direction opposite the predetermined direction, the unit frame having a leading side and a trailing side with respect to the predetermined direction; a plurality of photosensitive members provided corresponding to a plurality of colors and supported by the unit frame; a front-side grip part provided at the leading side of the unit frame; and a rear-side grip part provided at the trailing side of the unit frame, wherein the main body includes a duct on an upstream side of the rear-side grip part in the predetermined direction for exhausting air from inside the main body; and wherein the rear-side grip part has a ventilation opening formed to penetrate through the rear-side grip part in a direction in which air flows toward the duct.

2. The image-forming device according to claim 1, wherein the front-side grip part is configured to be used to pull the tandem photosensitive-member unit out of the main body and to lift the tandem photosensitive-member unit; and wherein the rear-side grip part is configured to be used to lift the tandem photosensitive-member unit.

3. The image-forming device according to claim 1, wherein both the front-side grip part and the rear-side grip part are positioned on an imaginary straight line extending in the predetermined direction, the imaginary straight line passing through a center point of the tandem photosensitive-member unit with respect to a width direction perpendicular to the predetermined direction.

4. The image-forming device according to claim 3, further comprising a plurality of developer-supplying units detachably installed to the unit frame for accommodating and supplying developer to the plurality of photosensitive members, each of the plurality of developer-supplying units having a developer-unit grip part positioned on the imaginary straight line.

5. The image-forming device according to claim 4, wherein the developer-unit grip part has a recessed part that opens toward a neighboring developer-supplying unit when the plurality of developer-supplying units is installed to the unit frame.

6. The image-forming device according to claim 4, wherein each of the plurality of developer-supplying units comprises a developer bearing member disposed in confrontation with one of the plurality of photosensitive members when the developer-supplying unit is installed to the unit frame, the developer bearing member being configured to bear developer and to develop an electrostatic latent image formed on the photosensitive member.

7. The image-forming device according to claim 4, wherein the tandem photosensitive-member unit further comprises a plurality of developer bearing members disposed in confrontation with the plurality of photosensitive members in a one-to-one correspondence, each of the plurality of developer bearing members being configured to bear developer and to develop an electrostatic latent image formed on the photosensitive member.

8. The image-forming device according to claim 1, wherein the front-side grip part is configured to be operated both in an installed state in which the tandem photosensitive-member unit is installed to the main body and in a removed state in which the tandem photosensitive-member unit has been removed from the main body; and wherein the rear-side grip part is configured to be operated in the removed state, and not to be operated in the installed state.

9. The image-forming device according to claim 1, wherein the front-side grip part comprises a handle having a base end pivotally supported at the unit frame and a free end configured to be pivotally movable about the base end.

10. The image-forming device according to claim 9, wherein the main body comprises: an access opening formed in the main body at a downstream side in the predetermined direction for installing and removing the tandem photosensitive-member unit; and a cover configured to be movable between a closed position for covering the access opening and an open position for exposing the access opening; wherein the handle is pivotally movable between an operating position in which the front-side grip part can be operated, and a stored position in which the front-side grip part cannot be operated; and wherein the handle is configured to move to the stored position in association with movement of the cover to the closed position in a state in which the tandem photosensitive-member unit is installed to the main body.

11. The image-forming device according to claim 10, wherein the handle is configured to pivotally move to the operating position in association with movement of the cover to the open position in a state in which the tandem photosensitive-member unit is installed to the main body.

12. The image-forming device according to claim 10, wherein the cover comprises a guide member that is configured to contact the handle when the cover is opened and closed, thereby guiding the handle to the operating position and to the stored position.

13. The image-forming device according to claim 1, wherein the main body comprises a recording-medium accommodating member configured to accommodate recording media and to be slidably installed to and removed from the main body, the recording-medium accommodating member being configured to be removed from the main body in a same direction as the predetermined direction.

14. The image-forming device according to claim 1, wherein the tandem photosensitive-member unit further comprises an interference preventing part that prevents the plurality of photosensitive members from interfering with a surface on which the tandem photosensitive-member unit is placed in a state in which the tandem photosensitive-member unit has been removed from the main body.

15. The image-forming device according to claim 14, wherein the interference preventing part comprises foot members that protrude from the unit frame to a position lower than the plurality of photosensitive members, thereby contacting the surface on which the tandem photosensitive-member unit is placed.

16. A tandem photosensitive-member unit comprising: a unit frame configured to be slidably installed to a main body in a predetermined direction and removed from the main body of an image-forming device in reverse direction opposite the predetermined direction, the unit frame having a leading side and a trailing side with respect to the predetermined direction; a plurality of photosensitive members provided corresponding to a plurality of colors and supported by the unit frame; a front-side grip part provided at the leading side of the unit frame; and a rear-side grip part provided at the trailing side of the unit frame, wherein the main body includes a duct on an upstream side of the rear-side grip part in the predetermined direction for exhausting air from inside the main body; and wherein the rear-side grip part has a ventilation opening formed to penetrate through the rear-side grip part in a direction in which air flows toward the duct the rear-side grip extending in a direction orthogonal with respect to the predetermined direction.

17. The tandem photosensitive-member unit according to claim 16, wherein the front-side grip part is configured to be used to pull the tandem photosensitive-member unit out of the main body and to lift the tandem photosensitive-member unit; and wherein the rear-side grip part is configured to be used to lift the tandem photosensitive-member unit.

18. The tandem photosensitive-member unit according to claim 16, wherein both the front-side grip part and the rear-side grip part are positioned on an imaginary straight line extending in the predetermined direction, the imaginary straight line passing through a center point of the tandem photosensitive-member unit with respect to a width direction perpendicular to the predetermined direction.

19. The tandem photosensitive-member unit according to claim 18, further comprising a plurality of developer-supplying units detachably installed to the unit frame for accommodating and supplying developer to the plurality of photosensitive members, each of the plurality of developer-supplying units having a developer-unit grip part positioned on the imaginary straight line.

20. The tandem photosensitive-member unit according to claim 19, wherein the developer-unit grip part has a recessed part that opens toward a neighboring developer-supplying unit when the plurality of developer-supplying units is installed to the unit frame.

21. The tandem photosensitive-member unit according to claim 19, wherein each of the plurality of developer-supplying units comprises a developer bearing member disposed in confrontation with one of the plurality of photosensitive members when the developer-supplying unit is installed to the unit frame, the developer bearing member being configured to bear developer and to develop an electrostatic latent image formed on the photosensitive member.

22. The tandem photosensitive-member unit according to claim 19, further comprising a plurality of developer bearing members disposed in confrontation with the plurality of photosensitive members in a one-to-one correspondence, each of the plurality of developer bearing members being configured to bear developer and to develop an electrostatic latent image formed on the photosensitive member.

23. The tandem photosensitive-member unit according to claim 16, wherein the front-side grip part is configured to be operated both in an installed state in which the tandem photosensitive-member unit is installed to the main body and in a removed state in which the tandem photosensitive-member unit has been removed from the main body; and wherein the rear-side grip part is configured to be operated in the removed state, and not to be operated in the installed state.

24. The tandem photosensitive-member unit according to claim 16, wherein the front-side grip part comprises a handle having a base end pivotally supported at the unit frame and a free end configured to be pivotally movable about the base end.

25. The tandem photosensitive-member unit according to claim 24, wherein the main body comprises: an access opening formed in the main body at a downstream side in the predetermined direction for installing and removing the tandem photosensitive-member unit; and a cover configured to be movable between a closed position for covering the access opening and an open position for exposing the access opening; wherein the handle is pivotally movable between an operating position in which the front-side grip part can be operated, and a stored position in which the front-side grip part cannot be operated; and wherein the handle is configured to move to the stored position in association with movement of the cover to the closed position in a state in which the tandem photosensitive-member unit is installed to the main body.

26. The tandem photosensitive-member unit according to claim 25, wherein the handle is configured to pivotally move to the operating position in association with movement of the cover to the open position in a state in which the tandem photosensitive-member unit is installed to the main body.

27. The tandem photosensitive-member unit according to claim 25, wherein the cover comprises a guide member that is configured to contact the handle when the cover is opened and closed, thereby guiding the handle to the operating position and to the stored position.

28. The tandem photosensitive-member unit according to claim 16, wherein the main body comprises a recording-medium accommodating member configured to accommodate recording media and to be slidably installed to and removed from the main body, the recording-medium accommodating member being configured to be removed from the main body in a same direction as the predetermined direction.

29. The tandem photosensitive-member unit according to claim 16, further comprising an interference preventing part that prevents the plurality of photosensitive members from interfering with a surface on which the tandem photosensitive-member unit is placed in a state in which the tandem photosensitive-member unit has been removed from the main body.

30. The tandem photosensitive-member unit according to claim 29, wherein the interference preventing part comprises foot members that protrude from the unit frame to a position lower than the plurality of photosensitive members, thereby contacting the surface on which the tandem photosensitive-member unit is placed.

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Description

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CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2005-234824 filed on Aug. 12, 2005, and Japanese Patent Application No. 2005-376111 filed Dec. 27, 2005. The entire content of each of these priority applications is incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to an image-forming device, such as a laser printer, and a tandem photosensitive-member unit that is detachably mounted in the image-forming device.

BACKGROUND

Tandem type image-forming devices such as color printers are well known in the art. This type of image-forming device includes a plurality of developer units and photosensitive drums and forms color images by sequentially forming toner images in each color on the respective photosensitive drums and subsequently transferring and superimposing the toner images in each color on paper. Conventional tandem image-forming devices require the user to replace the developer units and photosensitive drums for each color, thereby placing a great burden on the user.

One such image-forming device disclosed in U.S. Pat. No. 6,738,590 (corresponding to Japanese patent application publication No. 2003-50531) employs a method of replacing all of the developer units and photosensitive drums together by providing the developer units and photosensitive drums in a single integrated image-forming unit, whereby the image-forming unit is mounted in and removed from the main body of the image-forming device through the top thereof.

SUMMARY

However, when replacing the image-forming unit in this image-forming device, the user must support an image-forming unit that is much larger and heavier than a single developer unit and photosensitive drum, increasing the risk that the image-forming unit may be dropped.

In view of the foregoing, it is an object of the invention to provide a tandem photosensitive-member unit that facilitates mounting and removing operations for the tandem photosensitive-member unit. It is another object of the invention to provide an image-forming device in which such tandem photosensitive-member unit is detachably mounted.

In order to attain the above and other objects, according to one aspect, the invention provides an image-forming device. The image-forming device includes a main body and a tandem photosensitive-member unit The tandem photosensitive-member unit includes a unit frame, a plurality of photosensitive members, a front-side grip part, and a rear-side grip. The unit frame is configured to be slidably installed to and removed from the main body in a predetermined direction. The unit frame has a leading side and a trailing side with respect to the predetermined direction. The plurality of photosensitive members is provided corresponding to a plurality of colors and is supported by the unit frame. The front-side grip part is provided at the leading side of the unit frame. The rear-side grip part is provided at the trailing side of the unit frame.

According to another aspect, the invention also provides a tandem photosensitive-member unit. The tandem photosensitive-member unit includes a unit frame, a plurality of photosensitive members, a front-side grip part, and a rear-side grip part. The unit frame is configured to be slidably installed to and removed from a main body of an image-forming device in a predetermined direction. The unit frame has a leading side and a trailing side with respect to the predetermined direction. The plurality of photosensitive members is provided corresponding to a plurality of colors and is supported by the unit frame. The front-side grip part is provided at the leading side of the unit frame. The rear-side grip part is provided at the trailing side of the unit frame.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative aspects in accordance with the invention will be described in detail with reference to the following figures wherein:

FIG. 1 is a side cross-sectional view showing a color laser printer as an aspect of the image-forming device of the invention;

FIG. 2 is a side cross-sectional view of a drum subunit provided in the color laser printer of FIG. 1 on which a developer cartridge is mounted;

FIG. 3 is a side cross-sectional view of the developer cartridge shown in FIG. 2;

FIG. 4 is a perspective view from the left side of a drum unit in which the developer cartridges are mounted;

FIG. 5 is a perspective view from the left side of a drum unit in which one of the developer cartridges has been removed;

FIG. 6 is a plan view of the drum unit shown in FIG. 4;

FIG. 7 is a left side view of the drum unit shown in FIG. 4;

FIG. 8 is a cross-sectional view along a line VIII-VIII indicated in FIG. 7;

FIG. 9 is an exploded perspective view of the drum subunit;

FIG. 10 is a perspective view of the drum subunit;

FIG. 11 is a perspective view from the left side illustrating the assembly of a pair of side plates to a front beam, four drum subunits, and a rear beam in a juxtaposed relationship;

FIG. 12A is a perspective view from the right side illustrating the assembly of the pair of side plates to the front beam, four drum subunits, and rear beam in a juxtaposed relationship;

FIG. 12B is an enlarged view of FIG. 12A illustrating electrodes;

FIG. 13A is a side view illustrating the positioning of drum shafts in a side plate;

FIG. 13B is an enlarged view of FIG. 13A illustrating portions near a wire spring;

FIG. 13C is an explanatory diagram showing how the wire spring urges the drum shaft;

FIG. 14 is a perspective view from the left side illustrating the pair of side plates that have been assembled to the front beam, four drum subunits, and the rear beam in a juxtaposed relationship;

FIG. 15A is a perspective view from the right side illustrating the pair of side plates that have been assembled to the front beam, four drum subunits, and rear beam in a juxtaposed relationship;

FIG. 15B is an enlarged view of FIG. 15A illustrating electrodes;

FIG. 16 is a rear view of the developer cartridge;

FIG. 17 is a left side view of the developer cartridge;

FIG. 18 is a perspective view showing a drum unit mounted in a main casing of the laser printer;

FIG. 19 is a perspective view of the laser printer in FIG. 18 with a portion cut out;

FIG. 20 is a perspective view showing the drum unit partially withdrawn from the main casing;

FIG. 21 is a perspective view showing the drum unit after being removed from the main casing;

FIG. 22 is a perspective view from the left side of the drum unit (with a rotatable nearside grip part);

FIG. 23 is a perspective view showing the drum unit mounted in the main casing;

FIG. 24 is a perspective view showing the drum unit removed from the main casing;

FIG. 25 is a perspective view from the bottom left side of the drum unit provided with front feet and rear feet;

FIG. 26 is a left side view of the drum unit shown in FIG. 25;

FIG. 27A is a side view of a side plate illustrating the positioning of drum shafts in the side plate according to a first variation;

FIG. 27B is a enlarged view of FIG. 27A showing how the wire spring urges the drum shaft;

FIG. 28 is an exploded perspective view of a drum subunit according to a second variation;

FIG. 29 is a perspective view from the left side illustrating the assembly of a pair of side plates to a front beam, four drum subunits according to the second variation shown in FIG. 28, and a rear beam in a juxtaposed relationship;

FIG. 30 is a perspective view from the left side illustrating the pair of side plates after being assembled to the front beam, the four drum subunits shown in FIG. 28, and the rear beam in a juxtaposed relationship;

FIG. 31 is a perspective view showing a drum unit mounted in a main casing (with a rotatable near side grip part) of a printer according to a sixth variation;

FIG. 32A is a side cross-sectional view of the printer according to the sixth variation in a region including a front cover and a handle to illustrate the movement of the front cover toward a closed position and the rotation of the handle toward a stored position, in which a protruding part of a guide on the front cover is in contact with a distal end of the handle;

FIG. 32B is a side cross-sectional view of the printer according to the sixth variation, in which a parallel part of the guide is in contact with the distal end of the handle; and

FIG. 32C is a side cross-sectional view of the printer according to the sixth variation, in which the front cover in the closed position and the handle in the stored position.

DETAILED DESCRIPTION

A tandem photosensitive-member unit for an image-forming device according to some aspects of the invention will be described while referring to the accompanying drawings wherein like parts and components are designated by the same reference numerals to avoid duplicating description

1. General Structure of a Color Laser Printer

FIG. 1 is a side cross-sectional view showing a color laser printer 1 as an aspect of the image-forming device of the invention. FIG. 2 is a side cross-sectional view of a drum subunit provided in the color laser printer 1 of FIG. 1 on which a developer cartridge 22 is mounted. FIG. 3 is a side cross-sectional view of the developer cartridge 22 shown in FIG. 2.

As shown in FIG. 1, a color laser printer 1 is a horizontal tandem-type printer having a plurality of drum subunits 23 juxtaposed in a horizontal direction. The printer 1 includes a main casing 2 and, within the main casing 2, a feeding unit 4 for supplying sheets of a paper 3, an image-forming unit 5 for forming images on the paper 3 supplied from the feeding unit 4, and a discharge unit 6 for discharging the paper 3 after an image has been formed thereon.

In the following description, the right side of the printer 1 in FIG. 1 (side of the main casing 2 in which a drum access opening 162 is formed) will be referred to as the "front side," while the left side of the printer 1 in FIG. 1 will be referred to as the "rear side." Further, the near side in FIG. 1 with respect to the paper width direction will be referred to as the "left side," while the far side in FIG. 1 will be referred to as the "right side."

Unless otherwise stated below, directions in the following description of a drum unit 21 and developer cartridges 22 will conform to the state in which the drum unit 21 and developer cartridges 22 are mounted in the main casing 2.

(1) Feeding Unit

The feeding unit 4 includes a paper tray 7 for accommodating the paper 3 that can be slid into or removed from a tray-accommodating section 171, described later, in a lower section of the main casing 2 in a front-to-rear direction; a separating roller 8 and a separating pad 9 disposed above a front end of the paper tray 7 and in confrontation with each other; and a feeding roller 10 disposed on the rear side of the separating roller 8.

The feeding unit 4 includes a feeding-end paper-conveying path 11 for guiding the paper 3 conveyed from the paper tray 7. The feeding-end paper-conveying path 11 is substantially U-shaped in a side view for initially guiding the paper 3 forward and subsequently reversing directions toward the rear. The feeding-end paper-conveying path 11 has an upstream end positioned on the lower side of the U-shape adjacent to the separating roller 8, and a downstream end positioned on the upper side of the U-shape adjacent to a conveying belt 53 described later.

The feeding unit 4 also includes a paper dust roller 12 and a pinch roller 13 disposed in confrontation with each other along the feeding-end paper-conveying path 11 and positioned above and forward of the separating roller 8; and a pair of registration rollers 14 also disposed on the feeding-end paper-conveying path 11 above the paper dust roller 12 and pinch roller 13.

A paper-pressing plate 15 is provided inside the paper tray 7 for supporting the paper 3 in a stacked state. The paper-pressing plate 15 is pivotably supported on the rear end thereof, so that the front end can pivot downward to a resting position in which the paper-pressing plate 15 rests on a bottom plate of the paper tray 7 and can pivot upward to a feeding position in which the paper-pressing plate slopes upward from the rear end to the front end.

A lever 16 is provided in the lower front section of the paper tray 7 for lifting the front end of the paper-pressing plate 15 upward. The lever 16 is pivotably supported at a position below the front end of the paper-pressing plate 15 so that the front end of the lever 16 can move up and down.

By pivoting the lever 16, the lever 16 lifts the front end of the paper-pressing plate 15, shifting the paper-pressing plate 15 into the feeding position. When the paper-pressing plate 15 is in the feeding position, the topmost sheet of paper 3 stacked on the paper-pressing plate 15 is pressed against the feeding roller 10. When the feeding roller 10 rotates, the paper 3 is fed toward a position between the separating roller 8 and separating pad 9.

When the paper tray 7 is removed from the main casing 2, the paper-pressing plate 15 settles into the resting position. While the paper-pressing plate 15 is in the resting position, sheets of the paper 3 can be stacked on the paper-pressing plate 15. After the feeding roller 10 has fed the paper 3 to a position between the separating roller 8 and separating pad 9, the rotating separating roller 8 separates and conveys the paper 3 one sheet at a time. The sheet conveyed by the separating roller 8 passes between the paper dust roller 12 and pinch roller 13, at which time the paper dust roller 12 removes paper dust from the paper 3, and continues along the feeding-end paper-conveying path 11 toward the registration rollers 14.

After registering the paper 3, the registration rollers 14 convey the paper 3 to the conveying belt 53.

(2) Image-forming Unit

(2-1) Scanning Unit

The image-forming unit 5 includes a scanning unit 17, a process unit 18, a transfer unit 19, and a fixing unit 20. A single scanning unit 17 is disposed in the top section of the main casing 2. Although not shown in the drawings, the scanning unit 17 includes a laser light-emitting unit, a polygon mirror, and a plurality of lenses and reflecting mirrors. The laser light-emitting unit emits laser beams based on image data for each color. After passing through the lenses and reflecting off the reflecting mirrors, the laser beams irradiate respective photosensitive drums 24 corresponding to each color

(2-2) Process Unit

The process unit 18 is disposed below the scanning unit 17 and above the feeding unit 4. As will be described later, the process unit 18 includes a single drum unit 21, and four developer cartridges 22 corresponding to the four colors.

(2-2-1) Drum Unit

As will be described in detail later, the drum unit 21 is detachably mounted in a drum-accommodating section 161 of the main casing 2 from the front side of the main casing 2 in a front-to-rear direction. The drum unit 21 includes four drum subunits 23 for each of the four colors. Specifically, the four drum subunits 23 are a yellow drum subunit 23Y, a magenta drum subunit 23M, a cyan drum subunit 23C, and a black drum subunit 23K.

The drum subunits 23 are disposed parallel to each other at intervals in the front-to-rear direction. Specifically, the drum subunits 23 are arranged from the front side to the rear side in the order yellow drum subunit 23Y, magenta drum subunit 23M, cyan drum subunit 23C, and black drum subunit 23K. As will be described later, each drum subunit 23 includes a pair of side frame sections 71, and a center frame section 72 spanning between the side frame sections 71 (see FIGS. 9 and 10).

As shown in FIG. 2, each drum subunit 23 holds the photosensitive drum 24, a Scorotron charger 25, and a cleaning brush 68.

The photosensitive drum 24 extends in a width direction (hereinafter, the width direction will denote a left-to-right direction orthogonal to the front-to-rear direction and the vertical direction). The photosensitive drum 24 includes a main drum body 26 that is cylindrical in shape and has a positive charging photosensitive layer formed of polycarbonate on its outer surface, and a drum shaft 27 disposed along the axis of the main drum body 26.

Both widthwise ends of the drum shaft 27 are inserted into the side frame sections 71 described later (see FIG. 10) and are positioned by side plates 121 described later (see FIG. 7).

Rotational support members 30 (see FIG. 12A) are fitted onto both axial ends of the main drum bodies 26 so as to be incapable of rotating relative to the same but capable of rotating relative to the drum shafts 27. With this structure, the main drum bodies 26 are rotatably supported on the drum shafts 27. During an image-forming process, the photosensitive drum 24 is rotated by a driving force transmitted from a motor (not shown) provided in the main casing 2.

As shown in FIG. 2, the charger 25 is supported on the center frame section 72 described later diagonally above and rearward of the photosensitive drum 24. The charger 25 opposes the photosensitive drum 24 at a distance. The charger 25 includes a discharge wire 28 disposed in opposition to but separated from the photosensitive drum 24, and a grid 29 provided between the discharge wire 28 and photosensitive drum 24.

The discharge wire 28 is connected to a wire electrode 80 (see FIG. 12B) described later. The grid 29 is connected to a grid electrode 81 (FIG. 12B) described later.

During an image-forming operation, a high-voltage circuit board (not shown) provided in the main casing 2 applies a high voltage to the discharge wire 28 via the wire electrode 80 to produce a corona discharge from the discharge wire 28. At the same time, a high-voltage circuit board (not shown) provided in the main casing 2 applies a high voltage to the grid via the grid electrode 81 to apply a uniform positive charge to the surface of the photosensitive drum 24 while controlling the amount of charge supplied thereto.

The cleaning brush 68 is supported on the center frame section 72 described later at a position rearward of the photosensitive drum 24 and opposes and is in contact with the photosensitive drum 24. During an image-forming operation, the high-voltage circuit board (not shown) provided in the main casing 2 applies a cleaning bias to the cleaning brush 68 via a cleaning electrode 83 described later (see FIG. 12B).

(2-2-2) Developer Cartridge

As shown in FIG. 1, the developer cartridges 22 are detachably mounted in correspondence to the drum subunits 23 for each color. Specifically, the developer cartridges 22 include a yellow developer cartridge 22Y detachably mounted on the yellow drum subunit 23Y, a magenta developer cartridge 22M detachably mounted on the magenta drum subunit 23M, a cyan developer cartridge 22C detachably mounted on the cyan drum subunit 23C, and a black developer cartridge 22K detachably mounted on the black drum subunit 23K.

As shown in FIG. 3, each developer cartridge 22 includes a developer frame 31 and, within the developer frame 31, an agitator 32, a supply roller 33, a developing roller 34, and a thickness-regulating blade 35.

The developer frame 31 is formed in a box shape having an opening 36 on the lower end. A partitioning wall 39 is provided midway in the developer frame 31 with respect to the vertical for partitioning the interior of the developer frame 31 into a toner-accommodating chamber 37 and a developing chamber 38. A through-hole 40 is formed in the partitioning wall 39 to allow communication between the toner-accommodating chamber 37 and developing chamber 38.

The toner-accommodating chamber 37 accommodates toner corresponding to one of the four colors. More specifically, the toner-accommodating chamber 37 of the yellow developer cartridge 22Y accommodates yellow toner, the toner-accommodating chamber 37 of the magenta developer cartridge 22M accommodates magenta toner, the toner-accommodating chamber 37 of the cyan developer cartridge 22C accommodates cyan toner, and the toner-accommodating chamber 37 of the black developer cartridge 22K accommodates black toner.

The toner of each color is a nonmagnetic, single-component toner having a positive charge. The polymerized toner is spherical in shape and is obtained by co-polymerizing a polymerized monomer using a well-known polymerization method such as suspension polymerization. The polymerized monomer may be, for example, a styrene monomer such as styrene or an acrylic monomer such as acrylic acid, alkyl (C1-C4) acrylate, or alkyl (C1-C4) meta acrylate. The base particle of the toner is formed primarily of a binding resin that is compounded with a coloring agent of the corresponding color, a charge-controlling agent, wax, and the like and further includes an additive for improving fluidity.

A coloring agent in yellow, magenta, cyan, and black is compounded to produce each of these colors. The charge-controlling agent is a charge-controlling resin obtained by co-polymerizing an ionic monomer having an ionic functional group, such as ammonium salt, with a monomer that can be co-polymerized with an ionic monomer, such as a styrene monomer or an acrylic monomer. The additive may be powder of a metal oxide, such as silica, aluminum oxide, titanium oxide, strontium titanate, cerium oxide, or magnesium oxide; or an inorganic powder, such as a carbide powder or metal salt powder.

Windows 142 are also formed in the toner-accommodating chamber .37 for detecting the amount of toner remaining in the toner-accommodating chamber 37. The windows 142 are embedded in both side walls 141 of the developer frame 31 at positions opposing each other across the toner-accommodating chamber 37 (FIG. 8).

The agitator 32 is disposed in the toner-accommodating chamber 37 and includes a rotational shaft 41 rotatably supported in both side walls 141 of the developer frame 31, and an agitating member 42 provided on the rotational shaft 41 along the axial direction thereof and extending radially outward from the rotational shaft. During image formation, a driving force from a motor (not shown) provided in the main casing 2 is transmitted to the rotational shaft 41 via a passive coupling gear 144 (see FIG. 17), causing the agitating member 42 to move circularly within the toner-accommodating chamber 37.

The supply roller 33 is disposed inside the developing chamber 38 below the through-hole 40. The supply roller 33 includes a supply roller shaft 43 formed of metal that is rotatably supported in both side walls 141 of the developer frame 31, and a sponge roller 44 formed of an electrically conductive sponge material covering the periphery of the supply roller shaft 43. During image formation, a driving force from a motor (not shown) provided in the main casing 2 is transmitted to the supply roller shaft 43 via the passive coupling gear 144 to drive the supply roller 33 to rotate.

The developing roller 34 is disposed inside the developing chamber 38 diagonally below and rearward of the supply roller 33. The developing roller 34 includes a developing roller shaft 45 formed of metal and rotatably supported in both side walls 141 of the developer frame 31, and a rubber roller 46 formed of an electrically conductive rubber that covers the periphery of the developing roller shaft 45.

More specifically, the rubber roller 46 has a two layer structure including a rubber roller layer configured of an electrically conductive urethane rubber, silicon rubber, EPDM rubber, or the like containing fine carbon particles and the like; and a coating applied to the surface of the rubber roller layer and formed primarily of urethane rubber, urethane resin, polyimide resin, or the like. A developing roller electrode 82 described later (see FIG. 12B) is connected to the developing roller shaft 45.

The developing roller 34 is disposed against the supply roller 33 so as to generate pressure between the rubber roller 46 and sponge roller 44. The developing roller 34 is also exposed on the bottom of the developer cartridge 22 through the opening 36.

During image formation, a driving force from a motor (not shown) provided in the main casing 2 is transmitted to the developing roller shaft 45 via the passive coupling gear 144 (FIG. 17) for rotating the developing roller 34. A developing bias supplied from the high-voltage circuit board (not shown) provided in the main casing 2 is also applied to the developing roller 34 via the developing roller electrode 82.

The thickness-regulating blade 35 is disposed in the developing chamber 38 so as to press against the developing roller 34 from above. The thickness-regulating blade 35 includes a blade 48 configured of a metal leaf spring member, and a pressing part 49 provided on a distal end of the blade 48. The pressing part 49 is formed of an insulating silicon rubber and has a semicircular cross-section.

A base end of the blade 48 is fixed to the partitioning wall 39 by a fixing member 47, while the elastic force of the blade 48 causes the pressing part 49 on the distal end to contact the rubber roller 46 of the developing roller 34 from above.

(2-2-3) Developing Operation in the Process Unit In each developer cartridge 22, toner of the corresponding color accommodated in the toner-accommodating chamber 37 shifts toward the through-hole 40 by its own weight. As the agitator 32 agitates the toner, some of the toner is discharged through the through-hole 40 into the developing chamber 38.

Toner discharged through the through-hole 40 into the developing chamber 38 is supplied onto the supply roller 33. As the supply roller 33 rotates, the toner borne on the supply roller 33 is supplied to the developing roller 34. At this time, the toner is positively tribocharged between the supply roller 33 and the developing roller 34 as a developing bias is applied to the developing roller 34.

As the developing roller 34 rotates, toner supplied to the surface of the developing roller 34 passes between the pressing part 49 of the thickness-regulating blade 35 and the rubber roller 46 of the developing roller 34, thereby maintaining a thin layer of uniform thickness on the surface of the rubber roller 46.

In the meantime, as shown in FIG. 2, the charger 25 in the drum subunit 23 corresponding to the developer cartridge 22 generates a corona discharge for charging the surface of the photosensitive drum 24 with a uniform positive polarity. As the photosensitive drum 24 continues to rotate, a laser beam emitted from the scanning unit 17 is scanned at a high speed over the positively charged surface of the photosensitive drum 24, forming an electrostatic latent image on the photosensitive drum 24 corresponding to an image that will be formed on the paper 3.

Next, positively charged toner borne on the surface of the developing roller 34 comes into contact with the photosensitive drum 24 as the developing roller 34 rotates and is supplied to areas on the surface of the positively charged photosensitive drum 24 that were exposed to the laser beam and, therefore, have a lower potential. In this way, the latent image on the photosensitive drum 24 is developed into a visible image according to a reverse development process so that the photosensitive drum 24 bears a toner image corresponding to the relevant color.

Toner remaining on the photosensitive drum 24 after the transfer operation is recovered by the developing roller 34. Further, paper dust deposited on the photosensitive drum 24 from the paper 3 is removed by the cleaning brush 68.

(2-3) Transfer Unit

As shown in FIG. 1, the transfer unit 19 is disposed in the main casing 2 above the feeding unit 4 and extends in the front-to-rear direction beneath the process unit 18. The transfer unit 19 includes a drive roller 51, a follow roller 52, the conveying belt 53, transfer rollers 54, and a cleaning unit 55.

The drive roller 51 and follow roller 52 are disposed in opposition to each other across a distance in the front-to-rear direction. The drive roller 51 is disposed rearward of the black drum subunit 23K, while the follow roller 52 is disposed forward of the yellow drum subunit 23Y.

The conveying belt 53 is an endless belt formed of a synthetic resin film such as an electrically conductive polycarbonate or polyimide containing dispersed conductive particles such as carbon. The conveying belt 53 is looped around the drive roller 51 and follow roller 52.

During image formation, a driving force from a motor (not shown) provided in the main casing 2 is transferred to the drive roller 51 for rotating the same. When the drive roller 51 is driven to rotate, the conveying belt 53 travels in a circuit around the drive roller 51 and follow roller 52, while the follow roller 52 follows the movement of the conveying belt 53. The conveying belt 53 moves in the same direction as the surfaces of the photosensitive drums 24 at transfer positions in which the conveying belt 5.3 contacts the photosensitive drums 24 of the drum subunits 23.

The transfer rollers 54 are disposed inside the conveying belt 53 at positions opposing each photosensitive drum 24 with the conveying belt 53 interposed therebetween. The transfer rollers 54 are configured of a metal roller shaft covered with a rubber roller that is formed of an electrically conductive rubber. The transfer rollers 54 are rotatably provided so that the surfaces of the transfer rollers 54 move in the same direction as the conveying belt 53 at the transfer positions. During image formation, the high-voltage circuit board (not shown) provided in the main casing 2 applies a transfer bias to the transfer rollers 54.

The cleaning unit 55 is disposed below the conveying belt 53 and includes a primary cleaning roller 56, a secondary cleaning roller 57, a scraping blade 58, and a toner collector 59.

The primary cleaning roller 56 is disposed so as to contact the lower portion of the conveying belt 53 on the side opposite the upper portion of the conveying belt 53 that contacts the photosensitive drums 24 and transfer rollers 54. The primary cleaning roller 56 is configured to rotate in a direction that follows the circular movement of the conveying belt 53. During image formation, the high-voltage circuit board (not shown) provided in the main casing 2 applies a primary cleaning bias to the primary cleaning roller 56.

The secondary cleaning roller 57 is disposed below the primary cleaning roller 56 and in contact with the same and is configured to rotate so that the peripheral surface of the secondary cleaning roller 57 moves in the same direction as the primary cleaning roller 56 at the contact position. During image formation, the high-voltage circuit board (not shown) provided in the main casing 2 applies a secondary cleaning bias to the secondary cleaning roller 57.

The scraping blade 58 is disposed in contact with the secondary cleaning roller 57 from below.

The toner collector 59 is disposed below the primary cleaning roller 56 and secondary cleaning roller 57 for collecting toner that falls from the secondary cleaning roller 57.

The conveying belt 53 moving circuitously along the driving of the drive roller 51 and the following of the follow roller 52 conveys the paper 3 supplied from the feeding unit 4 toward the rear of the printer 1 so that the paper 3 sequentially passes transfer positions corresponding to each drum subunit 23. As the paper 3 is conveyed, toner images in each color borne on the photosensitive drums 24 of each drum subunit 23 are sequentially transferred onto the paper 3, forming a color image thereon.

For example, first the yellow toner image borne on the surface of the photosensitive drum 24 in the yellow drum subunit 23Y is transferred onto the paper 3 after which the magenta toner image borne on the surface of the photosensitive drum 24 in the magenta drum subunit 23M is transferred onto the paper 3 and superimposed over the yellow toner image already transferred. In the same way, the cyan toner image and black toner image borne on the surfaces of the photosensitive drums 24 in the cyan drum subunit 23C and black drum subunit 23K, respectively, are superimposed over the previously transferred toner images to form a color image on the paper 3.

Any toner deposited on the surface of the conveying belt 53 in the transfer operation described above is subsequently cleaned by the cleaning unit 55. First, the toner on the surface of the conveying belt 53 is transferred to the primary cleaning roller 56 by a primary cleaning bias and is subsequently transferred to the secondary cleaning roller 57 by a secondary cleaning bias. Next, the scraping blade 58 scrapes off toner that has been transferred onto the secondary cleaning roller 57. Toner scraped off the secondary cleaning roller 57 drops into the toner collector 59.

(2-4) Fixing Unit

The fixing unit 20 is disposed in the main casing 2, rearward of the black drum subunit 23K and opposite the transfer position in which the photosensitive drum 24 contacts the conveying belt 53 in the front-to-rear direction. The fixing unit 20 includes a heating roller 61 and a pressure roller 62.

The heating roller 61 is configured of a metal tube, the surface of which has been coated with a release layer. The metal tube accommodates a halogen lamp extending along the axial direction of the main casing 2 for heating the surface of the heating roller 61 to a fixing temperature.

The pressure roller 62 is disposed below and in confrontation with the heating roller 61. The pressure roller 62 presses against the heating roller 61 from the bottom thereof.

After a color image has been transferred onto a sheet of paper 3, the paper 3 is conveyed to the fixing unit 20. In the fixing unit 20, the color image is fixed to the paper 3 by heat as the paper 3 passes between the heating roller 61 and pressure roller 62.

(3) Discharge Unit

A discharge-end conveying path 63 is provided in the discharge unit 6. The discharge-end conveying path 63 is substantially U-shaped in a side view, with an upstream end positioned on the lower side adjacent to the fixing unit 20 and a downstream end positioned on the upper side adjacent to a discharge tray 64 formed on top of the main casing 2. Hence, the discharge-end conveying path 63 initially-guides the paper 3 rearward, then reverses directions and discharges the paper 3 in a forward direction.

A transfer roller 65 and a pinch roller 66 are disposed in confrontation with each other along the discharge-end conveying path 63 Further, a pair of discharge rollers 67 is disposed on the downstream end of the discharge-end conveying path 63. The discharge tray 64 is formed on top of the main casing 2 as a depression that grows gradually deeper toward the rear side. The discharge tray 64 functions to support sheets of discharged paper 3 in a stacked state.

After the paper 3 passes through the fixing unit 20, the transfer roller 65 and pinch roller 66 convey the paper 3 along the discharge-end conveying path 63 toward the discharge rollers 67 and the discharge rollers 67 discharge the paper 3 onto the discharge tray 64.

2. Drum Unit

FIG. 4 is a perspective view from the left side of the drum unit 21 in which the developer cartridges 22 are mounted. FIG. 5 is a perspective view from the left side of the drum unit 21 in which one of the developer cartridges 22 has been removed. FIG. 6 is a plan view of the drum unit 21 shown in FIG. 4. FIG. 7 is a left side view of the drum unit 21 shown in FIG. 4. FIG. 8 is a cross-sectional view along a line VIII-VIII indicated in FIG. 7. FIG. 9 is an exploded perspective view of the drum subunit 21. FIG. 10 is a perspective view of the drum subunit 21. FIG. 11 is a perspective view from the left side illustrating the assembly of the pair of side plates 121 to a front beam 96, four drum subunits 23, and a rear beam 111 in a juxtaposed relationship. FIG. 12A is a perspective view from the right side illustrating the assembly of the pair of side plates 121 to the front beam 96, four drum subunits 23, and rear beam 111 in a juxtaposed relationship. FIG. 12B is an enlarged view of FIG. 12A illustrating electrodes. FIG. 13A is a side view illustrating the positioning of drum shafts 27 in the side plate 121. FIG. 13B is an enlarged view of FIG. 13A illustrating portions near a wire spring 127. FIG. 13C is an explanatory diagram showing how the wire spring 127 urges the drum shaft 27. FIG. 14 is a perspective view from the left side illustrating the pair of side plates 121 that have been assembled to the front beam 96, four drum subunits 23, and the rear beam 111 in a juxtaposed relationship. FIG. 15A is a perspective view from the right side illustrating the pair of side plates 121 that have been assembled to the front beam 96, four drum subunits 23, and rear beam 111 in a juxtaposed relationship. FIG. 15B is an enlarged view of FIG. 15A illustrating electrodes.

Next, the drum unit 21 will be described with reference to FIGS. 4 through 15B.

As shown in FIG. 4, the drum unit 21 includes the four drum subunits 23 corresponding to the four colors and juxtaposed in the front-to-rear direction; the front beam 96 and the rear beam 111 disposed on front and rear sides of the four drum subunits 23; and the pair of side plates 121 disposed on widthwise ends of the front beam 96, the four drum subunits 23, and the rear beam 111. The four drum subunits 23 (frame construction except for the photosensitive drums 24 and the like), the front beam 96, the rear beam 111, and the pair of side plates 121 constitute a unit frame.

The four drum subunits 23, the front beam 96, the rear beam 111, and the pair of side plates 121 constituting the drum unit 21 can be slidably mounted into or removed from the drum access opening 162 of the main casing 2 as an integrated unit.

(1) Drum Subunits

As shown in FIGS. 9 and 10, the drum subunit 23 includes the pair of side frame sections 71 disposed in opposition to each other over a distance in the width direction, and the center frame section 72 that spans between the side frame sections 71.

(1-1) Side Frame Sections

Each of the side frame sections 71 is formed of a synthetic resin material and has a substantially rectangular plate shape in a side view. More specifically, the side frame sections 71 are shaped substantially like parallelograms in a side view and slope downward and to the rear.

Guide grooves 73 are formed in the inner wall surfaces of the side frame sections 71 at positions opposing each other in the width direction for guiding the developer cartridge 22 as the developer cartridge 22 is mounted in or removed from the drum subunit 23.

The guide grooves 73 in the inner wall surfaces of the side frame sections 71 are formed substantially in a vertical direction from the top edge near the rear side of the side frame section 71 to a point near the lower edge on the front side of the side frame section 71. The upstream ends of the guide grooves 73 are wider and open toward the top. The downstream ends of the guide grooves 73 (deepest parts) are disposed at positions corresponding to the developing roller shafts 45 when the developer cartridge 22 is mounted on the drum subunit 23 so that the developing roller 34 contacts the photosensitive drum 24. The guide grooves 73 are formed as depressions in the inner wall surfaces of the side frame section 71 depressed outward in the width direction. As shown in FIG. 16, electrically conductive collar members 50 are slidably received in the guide grooves 73 for covering both widthwise ends of the developing roller shaft 45.

As shown in FIG. 9, bosses 75 are formed in the upper side of the side frame sections 71 at positions forward of the guide grooves 73. The bosses 75 are cylindrical in shape and have a hollow that penetrates the side frame section 71. The bosses 75 protrude outward in the width direction from the outer wall of the side frame sections 71. When the developer cartridge 22 is mounted on the drum subunit 23, the windows 142 (see also FIG. 17) of the developer cartridge 22 oppose each other in the width direction through the bosses 75, as shown in FIG. 8.

Drum support units 76 (FIG. 9) are formed in the side frame sections 71 for supporting the photosensitive drum 24. Each drum support unit 76 includes a receiving part 77 formed in the inner wall surface of the side frame section 71 on the lower end of the same and having a cylindrical shape that is depressed outward in the width direction. The receiving part 77 receives a cylindrical axial insertion part 90 of the center frame section 72 described next. Axial insertion through-holes 78 are formed in the center of the receiving parts 77 and penetrate the side frame sections 71 in the thickness direction.

Two threaded through-holes 79 are formed in each side frame section 71 on the rear edge thereof, penetrating the side frame sections 71 in the thickness direction. Screws 92 are inserted into the threaded through-holes 79 for fixing the side frame sections 71 to the center frame section 72. One of the threaded through-holes 79 is formed in the lower rear edge of the side frame section 71, while the other is formed midway along the rear edge.

Protruding ridges 84 extending in the front-to-rear direction are formed on each side frame section 71 above the boss 75. The protruding ridges 84 are formed as narrow seams extending in the front-to-rear direction and protruding outward in the width direction from the outer wall surface of the side frame sections 71.

As shown in FIG. 9, a coupling inner through-hole 74 is formed in the side frame section 71 on the left side midway in the guide groove 73 at a position corresponding to the passive coupling gear 144 (FIG. 17) of the developer cartridge 22 in the width direction when the developer cartridge 22 is mounted on the drum subunit 23. The coupling inner through-hole 74 is a circular hole penetrating the left side frame section 71 in the width direction.

A screw receiving part 85 is also provided in the left side frame section 71 between the coupling inner through-hole 74 and axial insertion through-hole 78. A screw 136 (see FIG. 11) is screwed into the screw receiving part 85 to fasten the side plate 121 to the drum subunit 23. The screw receiving part 85 is cylindrical in shape and protrudes outward in the width direction from the outer wall surface of the side frame section 71.

As shown in FIG. 12B, the wire electrodes 80, grid electrodes 81, developing roller electrodes 82, and cleaning electrodes