Image forming apparatus including drum unit attachable and detachable along drum shaft

An image forming apparatus includes a drum unit configured to be attachable to and detachable from the body through inserting the drum shaft into the hollow portion of the photoreceptor drum, a plurality of ribs formed on the drum unit, a guide rail formed in a body, and a plurality of cutouts that is formed in the guide rail is configured to engage with the plurality of ribs when the drum unit is positioned at a regular position. The drum shaft and the guide rail are configured with respect to each other such that a center of the drum shaft is substantially coaxial with a center of the photoreceptor drum when the drum unit slides relative to the body in a state in which the plurality of ribs is placed on the guide rail.

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2010-078193, filed on 30 Mar. 2010, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus configured such that a drum unit is attachable to and detachable from a body along a drum shaft.

2. Related Art

In an image forming apparatus such as a copy machine or a printer, an image supporting unit, which has a surface uniformly charged by a charging device, is optically scanned by an optical scanning device, and an electrostatic latent image corresponding to image information is formed on the surface of the image supporting unit such as a photoreceptor drum. Thereafter, the electrostatic latent image is developed by a developing device using toner as a developer, and visualized as a toner image. The toner image is transferred onto a sheet of paper by a transfer device, and then heated, pressurized and fixed onto the sheet of paper by a fixing device. The sheet of paper onto which the toner image is fixed is discharged outside the image forming apparatus, so that a series of image forming steps is terminated.

Incidentally, an image forming apparatus is known in which a photoreceptor drum, a charging device and the like are unitized into a drum unit for easy maintenance and the drum unit is configured to be attachable to and detachable from a body. In such an image forming apparatus employing the features described above, a drum shaft for driving the drum unit is provided in the body such that the drum unit is attached to the body by inserting the drum shaft into an axial center (hollow portion) of the photoreceptor drum and pushing the drum unit along a guide rail and the drum shaft, which are provided in the body. When the attachment of the drum unit is completed, the drum unit is positioned at a regular position by a positioning part provided in the body.

As a setup of positioning an optical deflection unit with respect to a frame of the body, it is known that a V-shaped notch is provided in a bottom surface on an end side of the optical deflection unit and a flange is provided on another end of the optical deflection unit. This setup causes the V-shaped notch formed in the optical deflection unit to engage with a reference shaft of the drum unit, such that the flange of the optical deflection unit is positioned above a height adjustment screw.

Another setup is also known, in which a process cartridge (a drum unit) is inserted into a cartridge slot of the body. In such a setup, a guide portion formed on the process cartridge is inserted along a pair of guide rails. Such a setup includes a technical feature that allows one of the guide rails to be movable in order to implement better handling associated with attachment and detachment of the process cartridge with respect to the body of the image forming apparatus. In the setup described above, the process cartridge is supported by an abutting member of the body when the one of guide rails is lowered through operation of a lever of the body. Accordingly, the positioning part of the process cartridge engages with a groove of the body, so that the process cartridge is positioned with respect to the body.

SUMMARY OF THE INVENTION

Another setup is known in which a drum shaft is inserted into an axial center (hollow portion) of a photoreceptor drum and a drum unit is slidingly attached to and detached from a body along a drum shaft and a guide rail. However, an image forming apparatus employing such a setup has posed a drawback. It may be that since the drum unit places a load on the drum shaft when the drum unit is attached to or detached from the body, the drum shaft deforms, so that rotation of the drum shaft is not smoothly transferred to the photoreceptor drum.

The present invention provides an image forming apparatus that is configured to smoothly attach and detach the drum unit with respect to the body without placing a load on the drum shaft such that the deformation of the drum shaft is prevented.

The present invention relates to an image forming apparatus that includes a body, a drum shaft attached to the body, a plurality of ribs, a guide rail and a plurality of cutouts. The drum unit, which includes a photoreceptor drum with a hollow portion formed in an axial center thereof, is configured to be attachable to and detachable from the body through inserting the drum shaft into the hollow portion of the photoreceptor drum. The plurality of ribs is formed on the drum unit along an attaching and detaching direction of the drum unit with respect to the body. The guide rail, which is formed in the body, is configured to allow the drum unit to slide when the plurality of ribs is placed on the guide rail. The plurality of cutouts that is formed in the guide rail is engaged with the plurality of ribs when the drum unit is positioned at a regular position in the body after completion of attaching the drum unit to the body. The drum shaft and the guide rail are configured with respect to each other such that a center of the drum shaft is substantially coaxial with a center of the photoreceptor drum when the drum unit slides relative to the body in a state in which the plurality of ribs is placed on the guide rail.

According to the present invention, an image forming apparatus is provided that avoids deformation of the drum shaft by smoothly attaching and detaching the drum unit with respect to the body without placing a load on the drum shaft.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a cross-sectional view of a laser printer1as a first embodiment of an image forming apparatus according to the present invention. In the laser printer1shown inFIG. 1, a tilted and concave ejected paper tray3is provided in a central portion of a top face of a rectangular box-shaped body2. In addition, a manual feeding tray4that is openable and closable is provided in an upper portion of a side of the body2. The manual feeding tray4and a paper feeding roller5for manual feeding, which is rotatably provided inside the body2, compose a manual feeding part6.

The laser printer1forms an image on a sheet of paper P as a recording material based on image data transmitted from a terminal (not illustrated) or the like, while feeding the sheet of paper P along a paper feed path S provided inside the body2. The paper feed path S is substantially L-shaped in a side view and extends toward the ejected paper tray3.

The laser printer1includes a paper feeding part7, an image forming part8, a fixing device9, and a concave ejection part10. The paper feeding part7is provided in a lower portion of the body2. The image forming part8is provided in a substantially central portion above the paper feeding part7, inside the body2. The fixing device9is disposed downstream of the image forming part8. The ejection part10is provided above the fixing device9on an upper side of the body2.

The paper feeding part7stores a plurality of sheets of paper P stacked inside a paper feeding cassette11shaped like an open-top rectangular tray. The paper feeding part7is provided with a pick-up roller12for picking up a sheet of paper P at a time from the paper feeding cassette11, and a feeding roller13and a retarding roller14that separate and feed the sheet of paper P picked up to the paper feed path S, sheet by sheet. The paper feed path S is provided with a pair of resist rollers15. The pair of resist rollers15causes the fed sheet of paper P to temporarily wait and to be fed to the image forming part8at predetermined timing.

The image forming part8forms an image corresponding to image data on the sheet of paper P that has been fed sheet by sheet from the manual feeding part6or the paper feeding part7. The image forming part8includes: a photoreceptor drum16as an image supporting unit rotatably disposed in a substantially central portion inside the body2; a charging device17disposed in a periphery of the photoreceptor drum16; a developing device18as developing means; an image transfer roller19as image transfer means; a cleaning device20; an optical scan device (laser scanner unit)21disposed above these components; and a toner hopper22to contain toner for refilling.

The fixing device9is configured to fix a toner image transferred to the sheet of paper P by the image forming part8. The fixing device9is provided with a fixing roller23and a pressurizing roller24that rotate in pressure contact with each other. The fixing roller23is provided with heating means such as a heater. The pressurizing roller24is pressurized by biasing means such as a spring with a predetermined pressure against the fixing roller23, and a fixing nip is formed between the fixing roller23and the pressurizing roller24.

The ejection part10is configured to eject the sheet of paper P, onto which the toner image has been fixed by the fixing device9, to outside the body2. The ejection part10is provided with a pair of paper ejection rollers25and26, disposed one above the other, a plurality of feed guiding ribs27shaped like a vertical rib, and the ejected paper tray3. The pair of paper ejection rollers25and26is disposed at an end of the paper feed path S. The plurality of feed guiding ribs27guides the sheet of paper P being fed from the fixing device9along the paper feed path S, to the pair of paper ejection rollers25and26. The ejected paper tray3provides a place on which sheets of paper P that have been ejected to outside the body2are collected.

Operation to form images performed by the laser printer1configured as described above will be hereinafter described.

A terminal such as a personal computer, for example, transmits a print start signal to the laser printer1. Subsequently, the photoreceptor drum16is rotationally driven at a predetermined processing speed in a direction of an arrow shown inFIG. 1(clockwise direction) by a driving means (not illustrated) in the image forming part8. A surface of the photoreceptor drum16is uniformly charged at a predetermined potential by the charging device17. Thereafter, the optical scanning device21outputs a laser beam based on the image data transmitted from the terminal and casts the laser beam onto the surface of the photoreceptor drum16. As a result, an electrostatic latent image corresponding to the image data is formed on the surface of the photoreceptor drum16. The electrostatic latent image formed on the surface of the photoreceptor drum16is developed by the developing device18using toner as a developer, and visualized as a toner image.

In a case of cassette feeding, a topmost sheet of paper P is first picked up by the pick-up roller12, followed by another sheet of paper T at a time from the sheets of paper P housed inside the paper feeding cassette11of the paper feeding part7. Then, the sheets of paper P are separated by the feeding roller13and the retarding roller14sheet by sheet and fed to the pair of resist rollers15. At the pair of resist rollers15, a sheet of paper P is temporarily maintained to stand by and is fed to the image forming part8at predetermined timing synchronized with the toner image on the surface of the photoreceptor drum16.

In the image forming part8, the sheet of paper P fed to a transfer nip between the photoreceptor drum16and the image transfer roller19is fed while being pressed against the photoreceptor drum16by the transfer roller19. Accordingly, the toner image on the surface of the photoreceptor drum16is drawn to the transfer roller19, and transferred to the sheet of paper P that has been fed to the transfer nip. The sheet of paper P onto which the toner image has been transferred is fed to the fixing device9. In the fixing device9, the sheet of paper P, onto which the toner image has been transferred, is fed, heated and pressurized while being sandwiched by a fixing nip formed between the fixing roller23and the pressurizing roller24. In this manner, the toner image transferred to the sheet of paper P is fixed. Residual toner, which remains on the surface of the photoreceptor drum16after the transfer of the toner image to the sheet of paper P, is removed by the cleaning device20. The photoreceptor drum16whose surface has been cleaned is ready for a next image forming operation.

The sheet of paper P onto which the toner image has been fixed by the fixing device9is fed to an upper side of the paper feed path S toward the ejection part10. The sheet of paper P is guided to the pair of paper ejection rollers25,26along the feed guiding ribs27. Thereafter, the sheet of paper P is ejected to outside the body2while being sandwiched between the pair of paper ejection rollers25,26. The sheet of paper P is placed on the ejected paper tray3provided in the upper portion of the body2. As a result, a series of image forming operations is completed.

When a user manually feeds a sheet of paper P, the sheet of paper P placed on the manual feeding tray4of the manual feeding part6is fed to the pair of resist rollers15by the paper feeding roller S for manual feeding. Thereafter, an image is formed on the sheet of paper P in a similar process to the above described. The sheet of paper P on which the image has been formed is placed on the ejected paper tray3outside the body2.

In the laser printer1according to the present embodiment, the photoreceptor drum16and the charging device17are unitized into a drum unit30(described later, refer toFIGS. 2 and 3) for the sake of easy maintenance and the like. The drum unit30is configured to be attachable to and detachable from the body2.

An attachment/detachment structure of the drum unit30and steps of attaching it to the body2will be described hereinafter with reference toFIGS. 2 to 5.

FIG. 2is a front view showing the attachment/detachment structure of the drum unit;

FIG. 3is a perspective view of the drum unit;

FIG. 4is an enlarged detailed view of a portion A ofFIG. 3; and

FIGS. 5A to 5Care diagrams schematically showing a positional relationship between ribs on the drum unit and cutouts in a guide rail when the drum unit is installed.

As shown inFIGS. 2 and 3, a housing31of the drum unit30rotatably supports the photoreceptor drum16. In an axial center of the photoreceptor drum16, a hollow portion16A is formed to penetrate in a longitudinal direction (a direction vertical to a paper surface ofFIG. 2). In addition, on both sides of an upper portion of the housing31, as shown inFIGS. 3 and 4, three ribs32a,32band32c(FIGS. 3 and 4show only ribs on one side) are formed at appropriate intervals along the longitudinal direction.

As shown inFIG. 2, on a rear side of the apparatus main body2(a rear side of a paper surface ofFIG. 2), a drum shaft33is horizontally supported toward a front side. In addition, on right and left sides of a main frame34, two L-shaped guide rails35are horizontally formed in face-to-face relation along a longitudinal direction (a direction vertical to a paper surface ofFIG. 2). As shown inFIGS. 5A to 5C, each of the guide rails35is provided with three cutouts36a,36band36cformed at appropriate intervals (the same intervals as the ribs32a,32band32c). The three cutouts36a,36band36ccorrespond to the three ribs32a,32band32cformed on the drum unit30. Here, lengths (lengths in the longitudinal direction) La, Lb and Lc of the ribs32a,32band32cand lengths (lengths in the longitudinal direction) La′, Lb′ and Lc′ of the cutouts36a,36band36care configured to be greater in increasing order from upstream (a front side, a left side ofFIG. 5C) to downstream of an insertion direction of the drum unit30(La<Lb<Lc, La′<Lb′<Lc′). In addition, the plurality of ribs32a,32band32care configured to be engageable with the corresponding cutouts36a,36band36c(La<La′, Lb<Lb′, Lc<Lc′).

When the drum unit30is attached to the body2, the horizontal drum shaft33provided in the body2is inserted into the hollow portion16A of the photoreceptor drum16, as shown inFIG. 2. The drum unit30is slidingly inserted deeper into the body2along the drum shaft33and the guide rails35, while the ribs32a,32band32c, which are formed on the right and left side of the upper portion of the housing31of the drum unit30, are placed on the guide rails35of the main frame34.

Here, in the present embodiment, the drum shaft33and the guide rails35provided in the body2are configured to be positioned such that a center of the drum shaft33is coaxial with a center of the photoreceptor drum16when the drum unit30is caused to slide toward the body2with the ribs32a,32band32cformed on the drum unit30being placed on the guide rails35. Accordingly, the drum unit30slides smoothly without placing a load on the drum shaft33when the drum unit30is attached to the body2. In this manner, it is possible to avoid deformation of the drum shaft33and allow smooth rotation of the photoreceptor drum16.

As described above, the lengths La, Lb and Lc of the ribs32a,32band32c, and the lengths La′, Lb′ and Lc′ of the cutouts36a,36band36c, are configured to be greater in increasing order from upstream (front side) (left side ofFIG. 5C) to downstream of an insertion direction of the drum unit30(La<Lb<Lc, La′<Lb′<Lc′). As shown inFIG. 5A, for example, the longest rib32con a deeper side (downstream of the insertion direction) travels beyond the shortest cutout36awithout falling thereinto (without engaging therewith (La′<Lc). In addition, as shown inFIG. 5B, the longest rib32con the deeper side (downstream of the insertion direction) travels beyond the second longest cutout36bin the center location without falling thereinto (Lb′<Lc). Similarly, the second longest rib32bin the center location travels beyond the shortest cutout36awithout falling thereinto (without engaging therewith) (La′<Lb). Accordingly, it is possible to cause the drum unit30to smoothly slide along the guide rails35, and to be attached to and detached from the body2(La′<Lb′<Lc, La′<Lb).

In this manner, attaching the drum unit30to the body2is completed. When the drum unit30is positioned and maintained at a regular position in the body2, as shown inFIG. 5C, the three ribs32a,32band32cformed on the drum unit30engage with the corresponding three cutouts36a,36band36cformed in the guide rails35. Accordingly, the drum unit30is caused to slide up to the regular position in an unrestricted state with respect to the guide rails35. As a result, the drum unit30is accurately positioned and maintained at the regular position in the body2, without being restricted by the guide rails35. The photoreceptor drum16is rotationally driven at a predetermined speed by a driving force exerted by a motor (not illustrated), which is an actuator provided in the body2.

The steps of attaching the drum unit30to the body2have been described. Similarly, it is possible to detach the drum unit30from the body2smoothly without placing a load on the drum shaft33by performing the steps in a reversed order.

As described above, according to the present invention, it is possible to cause the drum unit30to be smoothly attached to and detached from the body2without placing a load on the drum shaft33. Accordingly, it is possible to avoid deformation of the drum shaft33. In addition, it is possible to install the drum unit30at the regular position accurately positioned in the apparatus main body2.

It should be noted that, although the above description has been provided for the embodiment of the present invention applied to a laser printer, the present invention can be equally applied to other image forming apparatuses such as a copy machine, a facsimile machine and the like provided with a drum unit.