A shaft-receiving device connects a rotating member and a frame. The rotating member has a rotational axis extending in a first direction and at least one end in the first direction. The frame extends in a second direction perpendicular to the first direction and is formed with a through-hole having an inner peripheral surface. The shaft-receiving device includes a shaft-receiving portion and a pressing member. The one end is inserted into the shaft-receiving portion in the first direction. The shaft-receiving portion is inserted into the through-hole in the first direction and opposes the inner peripheral surface in the second direction. The pressing member opposes the inner peripheral surface in the second direction to press the rotating member toward the inner peripheral surface.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2011-050406 filed Mar. 8, 2011. The entire content of this application is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a shaft-receiving device, a drum unit equipped with the shaft-receiving device, and an image-forming device equipped with the drum unit.

BACKGROUND

One electrophotographic color printer well known in the art is a tandem-type color printer. This printer has four photosensitive drums corresponding to the colors yellow, magenta, cyan, and black and arranged in tandem and parallel to one another.

One such tandem color printer proposed in Japanese unexamined patent application publication No. 2007-72422 has a main casing, and four photosensitive drums that are detachably mounted as a unit in the main casing. This conventional color printer is provided with drum subunits for holding the photosensitive drums, and a pair of side plates disposed on both sides of the drum subunits with respect to the axial direction of the photosensitive drums. A developer cartridge is provided for each of the drum subunits. The developer cartridges each hold a developing roller and are detachably mounted between the side plates. The drum subunits, developer cartridges, and side plates are all detachably mounted in the main casing as a drum unit.

SUMMARY

It is an object of the present invention to provide a shaft-receiving device, drum unit, and image-forming device capable of positioning rotary members, such as photosensitive drums, relative to a frame with precision.

In order to attain the above and other objects, the invention provides a shaft-receiving device for connecting a rotating member and a frame, the rotating member having a rotational axis extending in a first direction and at least one end in the first direction, the frame extending in a second direction perpendicular to the first direction and being formed with a through-hole having an inner peripheral surface. The shaft-receiving device includes: a shaft-receiving portion into which the one end is inserted in the first direction, the shaft-receiving portion being inserted into the through-hole in the first direction and opposing the inner peripheral surface in the second direction; and a pressing member opposing the inner peripheral surface in the second direction to press the rotating member toward the inner peripheral surface.

According to another aspect, the present invention provides a drum unit includes: a photosensitive drum having a rotational axis extending in a first direction and at least one end in the first direction; a frame extending in a second direction perpendicular to the first direction and being formed with a through-hole having an inner peripheral surface; a shaft-receiving device including: a shaft-receiving portion into which the one end is inserted in the first direction, the shaft-receiving portion being inserted into the through-hole in the first direction and opposing the inner peripheral surface in the second direction; and a pressing member opposing the inner peripheral surface in the second direction to press the photosensitive drum toward the inner peripheral surface.

According to another aspect, the present invention provides an image-forming device includes: a photosensitive drum having a rotational axis extending in a first direction and at least one end in the first direction; a frame extending in a second direction perpendicular to the first direction and being formed with a through-hole having an inner peripheral surface; and a shaft-receiving device including: a shaft-receiving portion into which the one end is inserted in the first direction, the shaft-receiving portion being inserted into the through-hole in the first direction and opposing the inner peripheral surface in the second direction; and a pressing member opposing the inner peripheral surface in the second direction to press the photosensitive drum toward the inner peripheral surface.

DETAILED DESCRIPTION

Next, preferred embodiments of the present invention will be described while referring to the accompanying drawings.

The image-forming device of the preferred embodiments is a tandem color printer1. As shown inFIG. 1, the printer1includes a main casing2, and a drum unit3mounted in the main casing2. A cover4is provided on the front surface of the main casing2. By opening the cover4, the drum unit3can be mounted in or removed from the main casing2.

In the following description, the side of the main casing2on which the cover4is provided (the left side inFIG. 1) will be referred to as the “front side,” while the opposite side (the right side inFIG. 1) will be referred to as the “rear side.” The left and right sides of the main casing2will be based on the perspective of a user facing the front side of the printer1.

The drum unit3is provided with four photosensitive drums5corresponding to the four colors black, yellow, magenta, and cyan. The photosensitive drums5are arranged parallel to each other and are spaced at equal intervals in the front-to-rear direction in the order black, yellow, magenta, and cyan.

The drum unit3also includes a Scorotron charger6and a developer cartridge7for each of the photosensitive drums5. Each developer cartridge7includes a developing roller8for supplying toner to the corresponding photosensitive drum5. The developer cartridges7are detachably mounted in the drum unit3.

An exposure device9is disposed above the drum unit3for irradiating four laser beams corresponding to the four colors employed in the printer1.

In an image-forming operation, the chargers6apply a uniform charge to the surfaces of the corresponding photosensitive drums5through corona discharge, as the photosensitive drums5rotate. Subsequently, the exposure device9irradiates laser beams for selectively exposing the surfaces of the photosensitive drums5. Each laser beam selectively removes charge from the surface of the corresponding photosensitive drum5, forming an electrostatic latent image thereon. As the electrostatic latent image formed on the charger6rotates to a position opposite the corresponding developing roller8, the developing roller8supplies toner to the latent image, developing the latent image into a visible toner image on the surface of the photosensitive drum5.

Here, four LED arrays may be provided for the four photosensitive drums5in place of the exposure device9.

A paper cassette10accommodating sheets of a paper P is disposed in the bottom section of the main casing2. The paper P accommodated in the paper cassette10is conveyed onto a conveying belt11by various rollers. The conveying belt11is positioned so as to confront the four photosensitive drums5from below. Four transfer rollers12are disposed inside the loop formed by the conveying belt11at positions confronting each of the photosensitive drums5through the upper portion of the conveying belt11. When a sheet of paper P is conveyed onto the conveying belt11, the conveying belt11conveys the sheet sequentially through positions between the conveying belt11and each of the photosensitive drums5. As the sheet passes beneath each photosensitive drum5, the toner image carried on the surface of the photosensitive drum5is transferred onto the paper P by a transfer bias applied to the corresponding transfer roller12.

A fixing unit13is provided on the downstream side of the conveying belt11with respect to the direction in which the paper P is conveyed. After toner images are transferred onto a sheet of paper P, the sheet is conveyed to the fixing unit13, where the toner images are fixed to the sheet by heat and pressure. After the toner images are fixed in the fixing unit13, various rollers discharge the sheet onto a discharge tray14formed on the top surface of the main casing2.

2. Drum Unit

As shown inFIG. 2, the drum unit3is an integrated unit that includes the four photosensitive drums5, the four developer cartridges7, four drum subunits20, a front beam21, a rear beam22, a pair of left and right inner plates24and25(see alsoFIG. 3), and a pair of left and right outer plates27and28. The drum unit3is mounted in the main casing2(seeFIG. 1) and is slidably inserted into and removed therefrom.

The four drum subunits20are disposed at intervals in the front-to-rear direction between the left and right inner plates24and25. Each drum subunit20is molded of a synthetic resin. The drum subunit20is shaped substantially like a triangular prism elongated in the left-to-right direction with an opening on the lower front side. Each drum subunit20functions to hold the charger6, and a cleaning member15shown inFIG. 1for cleaning the surface of the corresponding photosensitive drum5.

(2) Front Beam

The front beam21is formed of a synthetic resin material and bridges the front end parts of the left and right inner plates24and25.

The front beam21holds a support shaft29. The support shaft29penetrates the front beam21, as well as the left and right inner plates24and25, and the left and right outer plates27and28in the left-to-right direction and protrudes outward from the left and right outer plates27and28.

A front handle30is integrally formed on the front surface of the front beam21at a position in the left-to-right center of the same. The front handle30is substantially U-shaped in a plan view, with both ends of the handle coupled to the front beam21.

The rear beam22is also formed of a synthetic resin material and bridges the rear end parts of the left and right inner plates24and25.

A rear handle31is integrally formed on the top surface of the rear beam22at a position in the left-to-right center of the same. The rear handle31is substantially U-shaped in a rear side view, with both ends of the handle coupled to the rear beam22. The rear handle31protrudes upward from the rear beam22with a forward slope from bottom to top.

The left and right inner plates24and25are produced in a sheet-metal stamping process using the same die and, hence, have the same shape. Only the structure of the left inner plate25is described below, but the right inner plate24has the same structure.

As shown inFIGS. 3 and 4, the left inner plate25has a substantially elongated rectangular shape and extends in the front-to-rear direction. The front and rear ends of the left inner plate25respectively confront the front beam21and rear beam22in the left-to-right direction.

The front end of the left inner plate25extends along an upward slant toward the front. A support shaft insertion hole51for inserting the support shaft29is formed in this front end part of the left inner plate25.

The rear end of the left inner plate25is substantially L-shaped in a side view. A positioning part53is formed in the rear end of the left inner plate25as a generally V-shaped notch in the rear edge thereof. As shown inFIG. 1, the positioning part53receives a main casing reference shaft34spanning between rear sides of the main casing2in the left-to-right direction when the drum unit3is mounted in the main casing2. The positioning part53contacts the main casing reference shaft34from the front and top.

Four drum support holes32are formed in the left inner plate25at regular intervals in the front-to-rear direction.

(4-1) Drum Support Holes

As shown inFIG. 5, each drum support hole32has an inner peripheral surface139configured of four straight parts60and four curved parts61a-61d.

The four straight parts60are configured of a front vertical straight part63aand a rear vertical straight part63bthat extend vertically and oppose each other in the front-to-rear direction, and a top horizontal straight part64aand a bottom horizontal part64bthat extend in the front-to-rear direction and oppose each other vertically. The rear vertical straight part63band the bottom horizontal straight part64bare used to position a flange member81of the photosensitive drum5described later.

The four curved parts61a-61dconnect pairs of orthogonal straight parts60so that the corners between the orthogonal straight parts60are rounded. In a side view, the drum support hole32appears generally square in shape with rounded vertices. As described later, the four straight parts60are formed to fix the shaft-receiving member90, and the four curved parts61a-61dare formed to accept the thermal extension of the right and left inner plates24and25.

A shaft-receiving engaging groove70is formed in the bottom edge of the left inner plate25at a position vertically aligned with the center of each drum support hole32. The shaft-receiving engaging groove70is a substantially rectangular groove that is recessed upward in the bottom edge. Clip grooves71are also formed in the bottom edge of the left inner plate25on the front and rear side of each shaft-receiving engaging groove70. The clip grooves71are substantially rectangular in shape and are recessed upward in the bottom edge.

Above each drum support hole32, the top edge of the left inner plate25slopes upward toward the front, drops downward at a position opposing the center of the corresponding drum support hole32, and then extends forward substantially parallel to the horizontal straight parts64aand64b. This configuration forms a step part in the top edge of the left inner plate25above each drum support hole32. The lower level of each step part is an engagement part72. The engagement part72is engaged by a first engaging part101(or a second engaging part110) of a right shaft-receiving member90(or a left shaft-receiving member91) described later.

The left and right outer plates27and28shown inFIG. 2are formed of fiber-reinforced resin, for example. The left and right outer plates27and28have a substantially elongated rectangular plate shape in a side view. Compared to the left and right inner plates24and25, the left and right outer plates27and28have a wider vertical dimension and about the same front-to-rear length. The front and rear end parts of the left and right outer plates27and28confront the front beam21and rear beam22in respective left and right directions.

The front ends of the left and right outer plates27and28have bottom edges that slope upward toward the front, forming a narrower vertical dimension than the midway parts of the same plates. The rear ends of the left and right outer plates27and28have lower edges that slope upward toward the rear, forming narrower vertical dimensions that the midway parts of the same plates.

A recessed part33is formed in the rear end of each of the left and right outer plates27and28. The recessed parts33have substantially the same shape as the positioning parts53formed in the left and right inner plates24and25(seeFIG. 4) and are formed at positions corresponding to the positioning parts53in the left-to-right direction. The recessed parts33do not interfere with the main casing reference shaft34when the drum unit3is mounted in the main casing2.

As shown inFIG. 6, each photosensitive drum5is provided with a cylindrical main drum body80, and two flange members81. One of the flange members81is fitted over each end of the main drum body80so as to be incapable of rotating relative to the main drum body80.

The outer surface of the main drum body80is formed of a positive-charging photosensitive layer.

The flange members81are formed of a synthetic resin material. When fitted into the ends of the main drum body80, a portion of the flange members81is inserted into the main drum body80. Drive transmission parts112(described later with reference toFIG. 2) provided in the main casing2are coupled to the left endfaces of the left flange member81through coupling grooves (not shown). With this construction, a drive force can be transmitted through the drive transmission parts112to the photosensitive drum5for driving the photosensitive drum5to rotate when the drum unit3is mounted in the main casing2, as shown inFIG. 1. The outer ends of the flange members81have an outer diameter that is smaller than the diameter of the drum support holes32formed in the left and right inner plates24and25.

The right flange member81is rotatably supported in the right inner plate24by a right shaft-receiving member90. The left flange member81is rotatably supported in the left inner plate25by a left shaft-receiving member91.

The shaft-receiving member90is formed of a synthetic resin material. As shown inFIGS. 7,8A and8B, the right shaft-receiving member90is integrally configured of a cylinder part92having a cylindrical shape, a seal part98for sealing one endface of the cylinder part92, a shaft retaining part93disposed on the center part of the seal part98within the space encircled by the cylinder part92and formed with a cylindrical shape concentric to the cylinder part92, and a collar part94shaped like an annular disc surrounding the peripheral surface of the cylinder part92and extending radially outward from a midpoint of the cylinder part92relative to its axial direction.

The outer diameter of the cylinder part92is approximately the same as the inner peripheral surface139of the drum support hole32formed in the right inner plate24(seeFIG. 4). The inner diameter of the cylinder part92is slightly larger than the outer peripheral diameter of the right flange members81.

A notch part95is formed in the cylinder part92. The notch part95is a cutout portion that extends along the circumferential direction of the cylinder part92on one axial side (the seal part98side), then from both circumferential ends of this cutout portion extends toward the other axial side of the cylinder part92.

Put another way, the notch part95cutout in the cylinder part92includes a pair of slits separated by an arc length having a central angle of approximately 30 degrees and extending from one side of the cylinder part92(the seal part98side) toward the other side; and another slit providing communication between the first pair of slits in the circumferential direction of the cylinder part92. The seal part98is also cut out radially inward with an arc length having a central angle of about 30 degrees so that the cutout portion of the seal part98is in communication with the slit cut out in the circumferential direction of the cylinder part92.

The resulting notch part95forms a general U-shape in the cylinder part92and collar part94when viewed from the side, as shown inFIG. 8B.

The rectangular-shaped part that is surrounded by the generally U-shaped notch part95in a side view constitutes a pressing member96. The pressing member96is elongated and curved in the circumferential direction and extends from the collar part94toward the seal part98.

A protruding part97is also formed on the inner peripheral surface of the pressing member96at the end nearest the seal part98. The protruding part97has a hook-shaped cross section (seeFIG. 13).

The protruding part97protrudes inward from the inner peripheral surface of the pressing member96into the interior space of the cylinder part92. When the right flange member81is inserted inside the cylinder part92of the right shaft-receiving member90, the protruding part97contacts and applies pressure to the right flange member81(seeFIG. 13).

A shaft insertion hole99is formed in the seal part98. The shaft insertion hole99penetrates the seal part98in its thickness direction. The shaft insertion hole99is formed in the center portion of the seal part98and communicates with the interior of the shaft retaining part93.

A rod-shaped shaft83is provided in the right shaft-receiving member90along the central axis of the cylinder part92(shaft retaining part93). One end of the shaft83is inserted into the shaft retaining part93, penetrating the shaft insertion hole99and protruding out from the seal part98. The other end of the shaft83is tapered.

Two first engaging parts101are formed on the outer periphery of the collar part94at positions opposite each other across the axis of the shaft83. Each first engaging part101is integrally configured of an extension part115, a support part116, and an engaging protrusion117.

The extension part115has a U-shape in a side view, the U-shape opening outward from the outer peripheral edge of the collar part94along a radial direction of the cylinder part92. The support part116has also a U-shape in a side view and covers the extension part115.

The engaging protrusion117is provided on the side of the first engaging part101nearest the seal part98. The engaging protrusion117passes out through the space defined by the U-shaped extension part115and support part116and protrudes out in a direction toward the seal part98side.

The distal end of the engaging protrusion117has a hook shape in cross section. A sloped surface118is formed on the distal end of the engaging protrusion117. The sloped surface118slopes from the distal end of the engaging protrusion117toward the base end in a direction that approaches the central axis of the cylinder part92. The gap formed between the edge of the sloped surface118on the base end side and the surface of the collar part94on the seal part98side is set approximately the same as the thickness of the right inner plate24in the left-to-right direction.

The left shaft-receiving member91is formed of a synthetic resin material. As shown inFIGS. 9 and 10, the left shaft-receiving member91is integrally configured of a cylinder part105having a cylindrical shape, and a collar part106formed on one circumferential edge of the cylinder part105. The collar part106has an annular plate shape and expands radially outward.

The cylinder part105has an outer diameter approximately equivalent to the diameter of the drum support holes32formed in the left inner plate25(seeFIG. 4) and an inner diameter slightly larger than the outer peripheral diameter of the left flange members81.

A notch part107is formed in the cylinder part105as a cutout portion that extends along the circumferential direction of the cylinder part105on one axial side (the collar part106side), then from both circumferential ends of this cutout portion extends toward the other axial side of the cylinder part105.

More specifically, the cylinder part105is cut out to form a pair of slits separated by an arc length having a central angle of approximately 30 degrees that extend from the collar part106side of the cylinder part105toward the other side, and another slit formed in the collar part106side of the cylinder part105that extends in the circumferential direction to provide communication between the first pair of slits. The notch part107is also formed with a cutout portion in the collar part106extending in a direction radially outward from the cylinder part105and having an arc length in the circumferential direction based on a central angle of approximately 30 degrees. The cutout portion in the collar part106is formed at a position for communicating with the circumferential cutout part formed in the cylinder part105.

Accordingly, the notch part107formed in the cylinder part105and collar part106has a general U-shape in a side view.

The rectangular-shaped part of the cylinder part105that is surrounded by the U-shaped notch part107in a side view constitutes a pressing member108. The pressing member108is elongated and curved in the circumferential direction and extends from a midway point of the cylinder part105in the axial direction toward the collar part106side.

A protruding part109is also formed on the inner peripheral surface of the pressing member108along the edge nearest the collar part106. The protruding part109has a hook-like shape in cross section (seeFIG. 14) and protrudes from the inner peripheral surface of the pressing member108into the internal space defined by the cylinder part105. The protruding part109is also formed so as to contact and apply pressure to the left flange member81when the left flange member81is inserted inside the cylinder part105from the collar part106side (seeFIG. 14).

Two second engaging parts110are formed on the outer periphery of the collar part106at positions opposite each other about the axis of the cylinder part105. Each second engaging part110is integrally provided with an extension part119, and an engaging protrusion120.

The extension part119has a generally rectangular shape in a side view and extends outward from the outer peripheral edge of the collar part106along a radial direction of the cylinder part105.

The engaging protrusion120is plate-shaped and extends from the distal end of the extension part119(the outer end with respect to the radial direction of the cylinder part105) toward the opposite side of the cylinder part105from the collar part106. Hence, together the extension part119and engaging protrusion120form an L-shape in cross section.

(8) Mounting the Photosensitive Drums in the Drum Unit

The photosensitive drums5are mounted in the drum unit3when the four drum subunits20, the front beam21, the rear beam22, and the pair of left and right inner plates24and25have been assembled, as shown inFIG. 3.

To assemble the drum unit3, the four drum subunits20are spaced at regular intervals in the front-to-rear direction. The drum subunit20is spaced in front of the frontmost drum subunit20, and the rear beam22is spaced a slight interval rearward of the rearmost drum subunit20.

Subsequently, the right inner plate24is disposed on the right side of the front beam21, the four drum subunits20, and the rear beam22, while the left inner plate25is disposed on the left side of the same. Next, the left and right inner plates24and25are assembled to the front beam21, the drum subunits20, and the rear beam22with a plurality of screws (not shown).

After assembling the left and right inner plates24and25on the front beam21, drum subunits20, and rear beam22, the photosensitive drums5can be mounted in this assembly.

First, the right shaft-receiving member90is mounted on the right end of a photosensitive drum5. Specifically, the right flange member81is inserted inside the cylinder part92of the right shaft-receiving member90. At this time, the protruding part97of the pressing member96formed on the cylinder part92elastically contacts the outer peripheral surface of the flange member81, pressing the right flange member81away from the pressing member96. Contrary, the pressing member96is pressed by the right flange member81and protrudes outward of the cylinder part92due to the resistance from the right flange member81. With the right shaft-receiving member90fitted around the right flange member81, the shaft83held in the shaft retaining part93is inserted inside the photosensitive drum5.

The right shaft-receiving member90fitted around the right end of the photosensitive drum5is subsequently mounted in the corresponding drum support hole32formed in the right inner plate24, as illustrated inFIG. 11. Specifically, the photosensitive drum5is positioned so that the seal part98of the right shaft-receiving member90opposes the drum support hole32from the left side thereof. Next, the entire photosensitive drum5is moved rightward so that the right shaft-receiving member90is inserted into the drum support hole32, with the outer peripheral surface of the cylinder part92contacting the four straight parts60formed in the drum support hole32. At this time, the sloped surfaces118formed on the engaging protrusions117of the first engaging parts101respectively contact the top edge (engagement part72) and bottom edge (shaft-receiving engaging groove70) of the right inner plate24from the left side thereof. As the right shaft-receiving member90continues to move rightward, the top and bottom edges of the right inner plate24slide over the corresponding sloped surfaces118and elastically deform the engaging protrusions117outward in the direction that the edges contact the sloped surfaces118. When the collar part94contacts the left side surface of the right inner plate24, further rightward movement of the right shaft-receiving member90is restricted. At this point, the top and bottom edges of the right inner plate24have slid over the sloped surfaces118, allowing the engaging protrusions117to return to their original shape and leaving the edges of the right inner plate24between the corresponding sloped surfaces118and the collar part94. Accordingly, the two first engaging parts101engage the engagement part72and shaft-receiving engaging groove70of the right inner plate24.

When the two first engaging parts101engage the engagement part72and shaft-receiving engaging groove70of the right inner plate24, the cylinder part92contacts the four straight parts60of the drum support hole32, thereby being fixed to the right inner plate24, while gaps are formed between the outer peripheral surface of the cylinder part92and the curved parts61of the drum support hole32to accept the thermal extension of the right inner plates24.

Further, when the two first engaging parts101engage the engagement part72and shaft-receiving engaging groove70of the right inner plate24, the pressing member96(protruding part97) is pressed inward of the cylinder part92by the inner peripheral surface139. As the result, the right flange member81is pressed toward the curved part61apositioned between the rear vertical straight part63band the bottom horizontal straight part64bby the pressing member96and contacts the inner surface of the cylinder part92. At the same time, the cylinder part92is also pressed toward between the rear vertical straight part63band the bottom horizontal straight part64b. In this state, as shown inFIG. 13, the protruding part97is opposed to the inner peripheral surface139of the drum support hole32formed in the right inner plate24when projected along the pressing direction of the pressing members96.

Thus, the right flange member81is positioned relative to the right inner plate24through the cylinder part92, thereby achieving proper positioning of the right end portion of the photosensitive drum5. Note that the right flange member81(photosensitive drum5) can rotate, although the right flange member81is sandwiched between the pressing member96and the inner surface of the cylinder part92.

Next, the left shaft-receiving member91is mounted in the left inner plate25and on the left end of the photosensitive drum5(the left flange member81), as shown inFIG. 12. Specifically, with the flange member81exposed from the drum support hole32of the left inner plate25, the cylinder part105of the left shaft-receiving member91is inserted between the outer peripheral surface of the flange member81and the drum support hole32.

At this time, the protruding part109of the pressing member108formed in the cylinder part105elastically contacts the outer peripheral surface of the flange member81, pressing the entire flange member81away from the pressing member108. Contrary, the pressing member108is pressed by the left flange member81and protrudes outward of the cylinder part105due to the resistance from the flange member81.

As with the right shaft-receiving member90described above, the cylinder part105of the left shaft-receiving member91is inserted into the drum support hole32with the outer peripheral surface of the cylinder part105contacting the four straight parts60inside the drum support hole32.

At the same time, the collar part106of the left shaft-receiving member91is in contact with the outer surface (left side surface) of the left inner plate25when the left shaft-receiving member91has been completely mounted in the drum support hole32. This contact restricts the left shaft-receiving member91from moving any further rightward, positioning the left shaft-receiving member91in the left-to-right direction (the axial direction of the photosensitive drum5). Further, the top engaging protrusion120contacts the top edge of the left inner plate25(the engagement part72) from above, while the bottom engaging protrusion120contacts the bottom edge of the left inner plate25(the shaft-receiving engaging groove70) from below, as shown inFIG. 12. Accordingly, the two second engaging parts110engage the shaft-receiving engaging groove70and engagement part72of the left inner plate25, thereby holding the left shaft-receiving member91in its left-to-right position.

When the two second engaging parts110engage the engagement part72and shaft-receiving engaging groove70of the left inner plate25, the cylinder part105contacts the four straight parts60of the drum support hole32, thereby being fixed to the left inner plate25, while gaps are formed between the outer peripheral surface of the cylinder part105and the curved parts61of the drum support hole32to accept the thermal extension of the right inner plates24.

Further, when the two second engaging parts110engage the engagement part72and shaft-receiving engaging groove70of the left inner plate25, the pressing member108(protruding part109) is pressed inward of the cylinder part105by the inner peripheral surface139. As the result, the left flange member81is pressed toward the curved part61apositioned between the rear vertical straight part63band the bottom horizontal straight part64bby the pressing member108and contacts the inner surface of the cylinder part105. At the same time, the cylinder part105is also pressed toward between the rear vertical straight part63band the bottom horizontal straight part64b. In this state, as shown inFIG. 14, the protruding part109is opposed to the inner peripheral surface139of the drum support hole32formed in the left inner plate25when projected along the pressing direction of the pressing member108.

Thus, the left flange member81is positioned relative to the left inner plate25through the cylinder part105, thereby achieving proper positioning of the left end portion of the photosensitive drum5. Note that the left flange member81(photosensitive drum5) can rotate, although the left flange member81is sandwiched between the pressing member106and the inner surface of the cylinder part105.

Next, as shown inFIG. 6, a clip member111is attached to the portion of the shaft83that protrudes further rightward than the seal part98of the right shaft-receiving member90. The clip member111is substantially U-shaped. The ends of the U-shaped clip member111are bent and engaged respectively in the clip grooves71of the right inner plate24, while the midpoint of the clip member111contacts the portion of the shaft83protruding rightward from the seal part98. Attaching the clip member111completes the operation for mounting the photosensitive drum5in the drum unit3.

After all four photosensitive drums5have been mounted in the drum unit3, the left and right outer plates27and28are disposed on the respective left and right outer sides of the left and right inner plates24and25. The left and right outer plates27and28are assembled to the left and right inner plates24and25, the front beam21, the drum subunits20, and the rear beam22by screws (not shown), thereby completing assembly of the drum unit3.

(9) Mounting Developer Cartridges in the Drum Unit

After the drum unit3has been assembled, the developer cartridges7corresponding to each color used by the printer1can be mounted in the drum unit3. As shown inFIG. 2, guide grooves113are formed on the inner surfaces of the left and right outer plates27and28. Four of the guide grooves113are formed in each of the left and right outer plates27and28at regular intervals in the front-to-rear direction. Each guide groove113is configured of a pair of ridges formed on the inner surfaces of the left and right outer plates27and28that extend from the top edge of the surface toward the photosensitive drum5. The developer cartridge7is mounted in the drum unit3by guiding the developer cartridge7downward along this pair of ridges.

As shown inFIG. 15, the direction in which the developer cartridge7is moving just before the developer cartridge7is completely mounted in the drum unit3is the same as a pressing direction B in which the flange members81are pressed by the pressing members96and108. Therefore, a contact direction A in which the peripheral surface of the developing roller8provided in the developer cartridge7contacts the peripheral surface of the photosensitive drum5is also the same as the pressing direction B.

3. Grounding the Photosensitive Drums

As shown inFIG. 13, a ground member82is provided on the right end of the photosensitive drum5inside the main drum body80(seeFIG. 6). The ground member82is disc-shaped, extending in a plane orthogonal to the axis of the main drum body80and contacts the inner peripheral surface of the main drum body80.

When the right shaft-receiving member90has been attached to the right flange member81, the shaft83provided on the right shaft-receiving member90is inserted inside the photosensitive drum5and contacts the ground member82. Through this structure, the photosensitive drum5and the shaft83are electrically connected. As shown inFIG. 6, the clip member111is attached to the right end of the shaft83. Since the ends of the clip member111are engaged in the clip grooves71formed in the right inner plate24, the shaft83and the right inner plate24are also electrically connected. Hence, the main drum body80of the photosensitive drum5is electrically connected with and can conduct electricity to the right inner plate24through the ground member82, shaft83, and clip member111.

When the drum unit3is mounted in the main casing2, as shown inFIG. 1, the main casing reference shaft34is fitted into the positioning parts53of the left and right inner plates24and25(seeFIG. 4) and is capable of grounding the left and right inner plates24and25. Since the right inner plate24, photosensitive drums5, and ground members82are electrically connected through the shafts83and clip members111, the photosensitive drums5can be ground through the ground members82, shafts83, clip members111, right inner plate24, and main casing reference shaft34.

4. Main Casing

(1) Mounting the Drum Unit in and Removing the Drum Unit from the Main Casing

To mount the drum unit3in the main casing2, first the cover4on the main casing2shown inFIG. 1is opened. The drum unit3is then inserted rearward into the main casing2and is guided therein. When the positioning parts53formed in the left and right inner plates24and25contact the main casing reference shaft34, the drum unit3is restricted from being pushed further rearward and at this point is completely mounted inside the main casing2.

To remove the drum unit3from the main casing2, the above procedure is performed in reverse.

(2) Inputting a Drive Force for the Photosensitive Drums

As shown inFIG. 2, drive transmission parts112for transmitting a drive force to the photosensitive drums are provided inside the main casing2at positions opposing the left ends of the photosensitive drums5in the left-to-right direction when the drum unit3is mounted in the main casing2. After the drum unit3is mounted in the main casing2, the drive transmission parts112are advanced rightward and couple with coupling grooves (not shown) provided in the left endface of each left flange member81. With this construction, a drive force can be transmitted from the drive transmission parts112to the respective photosensitive drums5for driving the photosensitive drums5to rotate.

After the drive transmission parts112are connected to the coupling grooves formed in the flange members81, the drive transmission parts112are advanced further rightward, whereby the entire drum unit3is moved rightward through the flange members81. In this way, positioning of the drum unit3in the left-to-right direction can be achieved.

5. Operations and Effects of the First Embodiment

(1) As described above, the cylinder part92is fixed to the right inner plate24and the left inner plate25by the four straight parts60of the drum support hole32. Further, the right and left flange members81are firstly fitted into the right and left shaft-receiving members90and91with play, and are secondly positioned through pressure by the pressing members96and108. Hence, the right and the left flange members81are positioned relative to the right inner plate24and the left inner plate25through the cylinder part92and105, respectively.

Thus, this play (margin) between the flange members81and the right and left shaft-receiving members90and91can absorb any difference in thermal expansion occurring between the right and left inner plates24and25. Therefore, even if the right inner plate24and the left inner plate25have differing degrees of thermal expansion, the right and the left flange members81are positioned relative to the right inner plate24and the left inner plate25through the cylinder part92, respectively. As the result, the influence of the thermal expansion is restrained. Consequently, the photosensitive drums5can be positioned relative to the right inner plate24and the left inner plate25, respectively, with precision, thereby maintaining the four photosensitive drums5parallel to one another, regardless of the ambient temperature. Accordingly, this construction can prevent image-forming irregularities, such as problems with color registration.

Further, since the cylinder parts92and105are also pressed toward a stable position formed between the rear vertical straight part63band the bottom horizontal straight part64b, the right and left flange members81are positioned relative to the right inner plate24and the left inner plate25through the cylinder part92, respectively, more precisely.

Further, when projected along the pressing directions of the respective pressing members96and108, the protruding parts97and109formed on the pressing members96and108are opposed to the inner peripheral surfaces139of the respective drum support holes32formed in the left and right inner plates24and25.

Accordingly, as illustrated inFIGS. 13 and 14, the force of pressure applied by the pressing members96and108is equal to the force of resistance by the left and right inner plates24and25in the pressing direction of the pressing members96and108, thereby avoiding bending of the left and right shaft-receiving members91and90.

Thus, this construction can accurately position the photosensitive drum5relative to the left and right inner plates24and25.

(2) Further, the protruding part97(109) is formed in the rectangular part surrounded by the notch part95(107), and specifically on the end of the rectangular part nearest the right inner plate24(left inner plate25) side. Forming this pressing member96(109) through such a simple construction can reduce manufacturing costs of the printer1. Further, since the pressing member96(109) is formed integrally with the right shaft-receiving member90(left shaft-receiving member91), this construction can use fewer parts than a structure that forms the pressing members96(109) and right shaft-receiving member90(left shaft-receiving member91) separately.

(3) The right shaft-receiving member90(left shaft-receiving member91) is also provided with the annular collar part94(106). The collar part94(106) contacts the inner surface (left surface) of the right inner plate24(the inner surface (right surface) of the left inner plate25) when the right shaft-receiving member90(left shaft-receiving member91) is fitted into the drum support hole32, thereby determining the position of the right shaft-receiving member90(left shaft-receiving member91) in the left-to-right direction. The first engaging parts101are also integrally formed with the collar part94(106). The first engaging parts101engage the shaft-receiving engaging groove70and engagement part72of the right inner plate24(left inner plate25) to hold the right shaft-receiving member90(left shaft-receiving member91) in its left-to-right position.

(4) The drive transmission parts112are also provided in the main casing2on the left side of the photosensitive drums5at positions opposing the left ends of the left flange members81relative to the left-to-right direction. Coupling grooves (not shown) that connect with the drive transmission parts112are provided in the left endfaces of the left flange members81. By coupling the drive transmission parts112with the coupling grooves, a drive force can be transmitted to the photosensitive drums5through the drive transmission parts112for driving the photosensitive drums5to rotate.

(5) When a developer cartridge7is mounted in the drum unit3, the outer peripheral surface of the developing roller8provided in the developer cartridge7presses against the photosensitive drum5in the contact direction A shown inFIG. 15. The pressing members96and108press the flange members81in the pressing direction B equivalent to the contact direction A. Hence, both the developing roller8and the pressing members96and108apply a force to the flange members81, enabling the flange members81to be positioned more precisely relative to the left and right inner plates24and25.

6. Second Embodiment

Next, a second embodiment of the present invention will be described with reference toFIGS. 16 through 20.

InFIGS. 16 through 20, like parts and components to those described in the first embodiment shown inFIGS. 1 through 15are designated with the same reference numerals to avoid duplicating description.

In the first embodiment, the pressing member108is configured of the portion of the cylinder part105surrounded by the notch part107, as shown inFIGS. 9 and 10.

However, the left shaft-receiving member91according to the second embodiment is provided with a pressing member125, as shown inFIGS. 16 and 17. The pressing member125has a U-shape including a first stem127, and a second stem128. The first stem127of the pressing member125constitutes a portion of the cylinder part105interposed between a pair of slits126. The second stem128is a portion folded back over the first stem127.

More specifically, the slits126are formed parallel to each other in the cylinder part105and separated by a distance in the circumferential direction of the cylinder part105, as shown inFIGS. 16 and 17. The slits126cut out in the cylinder part105extend toward the collar part106from the edge of the cylinder part105opposite the collar part106.

The pressing member125has a substantially U-shaped cross section (seeFIG. 20). The first stem127of the pressing member125constitutes the portion of the cylinder part105interposed between the slits126that extends from the collar part106to a midway point in the cylinder part105relative to the axial direction thereof. The second stem128of the pressing member125is formed by bending the free end of the cylinder part105interposed between the slits126at a midway point in the axial direction of the cylinder part105so that the free end overlaps the first stem127in the thickness direction. The second stem128is elastically deformed when bent at this midway point.

A protruding part129is formed on the inner surface of the second stem128along the edge nearest the collar part106. The protruding part129has a hook-shaped cross section (seeFIG. 20). The protruding part129protrudes inward from the inner surface of the second stem128along the collar part106side into the interior space of the cylinder part105. When the left shaft-receiving member91is fitted around the flange member81, the protruding part109contacts and applies pressure to the flange member81(seeFIG. 20).

(2) Drum Support Holes

The left shaft-receiving member91is fitted into a drum support hole32according to a second embodiment having the structure shown inFIG. 18. Specifically, the upper portion of the front vertical straight part63and the curved part61on the upper front side have been cut outward from the inner peripheral surface of the drum support hole32. The resulting part cut out in the inner surface of the drum support hole32constitutes a pressing member accommodating part130.

(3) Mounting the Left Shaft-Receiving Member in the Left Inner Plate and on the Photosensitive Drum

The left shaft-receiving member91described above is mounted in the left inner plate25and over the left end of the photosensitive drum5(the left flange member81). Specifically, with the left flange member81exposed from the drum support hole32of the left inner plate25, the cylinder part105of the left shaft-receiving member91is inserted between the outer peripheral surface of the left flange member81and the drum support hole32.

At this time, the pressing member125is accommodated in the pressing member accommodating part130provided in the left inner plate25, as shown inFIG. 19. Here, the outer peripheral surface of the first stem127constituting the pressing member125opposes the inner peripheral surface of the pressing member accommodating part130.

As shown inFIG. 20, the protruding part129of the second stem128elastically contacts the outer peripheral surface of the flange member81, pressing the entire flange member81away from the pressing member125. When the protruding part129of the second stem128is projected in the pressing direction of the pressing member125, the protruding part129is aligned with the inner peripheral surface139of the corresponding drum support hole32formed in the left inner plate25.

(4) Operations and Effects of the Second Embodiment

Since the pressing member125is elastically deformed when bending the pressing member125at the midway point, the pressing member125can apply stronger pressure than the pressing member108of the first embodiment to the left flange member81toward the curved part61between the first and second flat parts (the rear vertical straight part63and bottom horizontal straight part64). Therefore, the flange member81can be precisely positioned relative to the first and second flat surfaces with the outer peripheral surface of the flange member81contacting the inner peripheral surface of the left shaft-receiving member91, thereby achieving precise positioning of the flange member81in both vertical and front-to-rear directions.

When the protruding part129of the second stem128is projected along the pressing direction of the pressing member125, the protruding part129overlaps the inner peripheral surface139formed in the drum support hole32of the left inner plate25. Hence, as shown inFIG. 20, the force with which the pressing member125presses against the flange member81is equal to the force of resistance by the left inner plate25in the pressing direction of the pressing member125, thereby preventing the left shaft-receiving member91from bending.

The construction according to the second embodiment of the present invention can position the photosensitive drum5more accurately relative to the left inner plate25than the construction of the first embodiment described above.

The second embodiment described above gives one application of the present invention, but the present invention can be implemented by variations of this embodiment.

For example, the left shaft-receiving member91according to the second embodiment is provided with the pressing member125having the first stem127and second stem128. However, a pressing member with a similar structure may be provided on the right shaft-receiving member90.

InFIGS. 21 through 25, like parts and components to those described in the first embodiment shown inFIGS. 1 through 15are designated with the same reference numerals to avoid duplicating description.

In the first embodiment, the pressing member108is configured of the portion of the cylinder part105surrounded by the notch part107, as shown inFIGS. 9 and 10.

However, the left shaft-receiving member91according to the third embodiment has a notch part134, and a pressing member135, as shown inFIGS. 21 and 22. The notch part134is formed by cutting out a portion of the left shaft-receiving member91along the circumferential direction and at a prescribed width. The pressing member135is disposed in the notch part134. The pressing member135includes a spring member136.

More specifically, the notch part134is formed continuously of a first notch part132, and a second notch part133. The first notch part132is cut out in the collar part106side of the cylinder part105with an arc length having a central angle of about 30 degrees. The second notch part133is also cut radially outward in the collar part106with an arc length having a central angle of about 30 degrees, so that the second notch part133is in communication with the first notch part132.

The pressing member135is integrally formed of a pressing part138, and support parts137.

The pressing part138is formed in a curved shape having the same curvature as the inner peripheral surface of the cylinder part105. The pressing part138appears substantially rectangular when viewed along the radial direction.

A pair of the support parts137is provided one on each end of the pressing part138with respect to the axial direction of the pressing member135. The support parts137are separated from each other and grip the collar part106. Specifically, each support part137has two ends extending radially outward from the ends of the pressing part138with respect to the circumferential direction of the same, then bending away from each other tangentially to the collar part106.

The pressing member135is fitted into the notch part134, with the pressing part138confronting the interior space defined by the cylinder part105. In this state, end faces of the pressing part138relative to its circumferential direction and the support parts137each oppose the notch part134with a slight gap formed therebetween.

The spring member136is provided on the outer surface of the pressing part138relative to the radial direction of the cylinder part105and is interposed between the pair of support parts137.

(2) Drum Support Holes

The left shaft-receiving member91is fitted into a drum support hole32according to a third embodiment having the structure shown inFIG. 23. Specifically, the curved part61on the upper front side is projected further outward and forms a general U-shape in the inner peripheral surface of the drum support hole32when viewed from the side. The resulting cutout part in the inner surface of the drum support hole32constitutes a spring accommodating part140.

A spring guide141is formed in the center of the edge defining the spring accommodating part140so as to protrude into the interior space of the drum support hole32.

(3) Mounting the Left Shaft-Receiving Member in the Left Inner Plate and on the Photosensitive Drum

The left shaft-receiving member91described above is mounted in the left inner plate25and over the left end of the photosensitive drum5(the left flange member81). Specifically, the first the spring member136is mounted over the spring guide141. The pressing member135is disposed in the notch part134so as to press against the spring member136, while the support parts137pinch the spring accommodating part140in the thickness direction and the pressing part138opposes the spring guide141. Next, with the left flange member81exposed from the drum support hole32of the left inner plate25, the cylinder part105of the left shaft-receiving member91is inserted between the outer peripheral surface of the left flange member81and the drum support hole32.

At this time, the pressing part138of the pressing member135contacts the outer peripheral surface of the flange member81through the notch part134and is pressed against the flange member81by the urging force of the spring member136. Accordingly, the entire flange member81is pushed away from the pressing member135.

When the pressing part138of the pressing member135is projected in the pressing direction of the pressing member135, the pressing part138is aligned with the inner peripheral surface139of the corresponding drum support hole32formed in the left inner plate25.

(4) Operations and Effects of the Third Embodiment

By the urging force of the spring member136, the pressing member135presses the flange member81toward the curved part61positioned between the rear vertical straight part63and bottom horizontal straight part64. Hence, the pressure applied by the pressing member135can be precisely adjusted based on the spring constant of the spring member136.

With the left flange member81contacting the inner peripheral surface of the left shaft-receiving member91, the flange member81is positioned relative to the first and second flat surfaces, thereby achieving positioning of the flange member81in the vertical and front-to-rear directions.

When the pressing part138of the pressing member135is projected in the pressing direction of the pressing member135, the pressing part138is positioned opposite the inner peripheral surface139of the corresponding drum support hole32formed in the left inner plate25. Hence, as shown inFIG. 25, the force with which the pressing member135presses against the flange member81is equal to the force of resistance by the left inner plate25in the pressing direction of the pressing member135, thereby preventing the left shaft-receiving member91from bending.

The construction according to the third embodiment of the present invention can suitably adjust the force applied by the pressing member135and can accurately position the photosensitive drums5relative to the left inner plate25.

The third embodiment described above gives one application of the present invention, but the invention can be implemented by variations of this embodiment.

For example, the left shaft-receiving member91according to the third embodiment is provided with the pressing member135having the spring member136. However, a pressing member with a similar structure may be provided on the right shaft-receiving member90.

Further, the flange member81may be pressed toward a part other than the curved part61a.