Image forming apparatus having a removable photosensitive member unit

An image forming apparatus can include a body casing, a photosensitive member unit configured to be inserted into and withdrawn from the body casing, the photosensitive member unit can be moved between a first position where the photosensitive member unit is stored in the body casing and a second position where the photosensitive member unit is withdrawn from the body casing, and between the second position and a third position where the photosensitive member unit is withdrawn from the body casing. The image forming apparatus may further include a control member disposed in the body casing, the control member configured to move between a holding position in which the photosensitive member unit is prevented from moving between the second position and the third position and a release position where the photosensitive member unit is allowed to move between the second position and the third position.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2006-095210, filed on Mar. 30, 2006, the entire subject matter of which is incorporated herein by reference.

FIELD OF THE INVENTION

Illustrative aspects of the invention relate to an image forming apparatus such as a laser printer.

BACKGROUND

A known color image forming apparatus, such as a color laser printer, is provided with a photosensitive member cartridge including four photosensitive drums, corona dischargers and cleaning devices, which are disposed around the photosensitive drums. The photosensitive member cartridge is configured to be attached to and removed from a main body of the image forming apparatus.

In the image forming apparatus, the photosensitive member cartridge is provided on its frame with the four photosensitive members and their appendixes, i.e., the corona chargers and cleaning devices while they are relatively positioned. A pair of fixing rollers and a pair of ejecting rollers are mounted on a side plate that can turn concentrically with respect to the center of rotation of the follower roller. The side plate is turned, and the pair of fixing rollers and the pair of ejecting rollers are retracted, thereby defining an opening through which the photosensitive member cartridge is withdrawn out of the system. In the state where the photosensitive member cartridge has been withdrawn from the main body, the photosensitive member cartridge can be detached from the system and replaced by a new photosensitive member cartridge.

In the color image forming apparatus, the photosensitive member cartridge can be temporarily placed on the side plate previously turned when it is withdrawn from the main body. Thus, the user can change his/her grip on the withdrawn photosensitive member cartridge on the side plate and remove the cartridge.

However, for a size reduction of the apparatus, the side plate on which the photosensitive member cartridge is placed may be omitted or may be reduced in strength to such a degree that it cannot support the photosensitive member cartridge. In such configurations, the photosensitive member cartridge needs to be pulled out and immediately removed from the main body. In addition, as it is hard for the user to change his/her grip on the withdrawn photosensitive member cartridge, attaching and removing the photosensitive member cartridge may become difficult.

SUMMARY

Illustrative aspects of the invention can provide an image forming apparatus that can achieve a reduction in size and enable a photosensitive member unit to be removed from a body casing.

According to an aspect, an image forming apparatus includes a body casing, a photosensitive member unit configured to be inserted into and withdrawn from the body casing, the photosensitive member unit configured to move between a first position where the photosensitive member unit is stored in the body casing, and a second position where the photosensitive member unit is withdrawn from the body casing, the photosensitive member unit configured to move between the second position and a third position where the photosensitive member unit is withdrawn from the body casing, the photosensitive member unit configured to hold a photosensitive members. The image forming apparatus further includes a control member disposed in the body casing, the control member configured to move between a holding position in which the photosensitive member unit is prevented from moving between the first position and the third position and a release position where the photosensitive member unit is allowed to move between the second position and the third position.

DETAILED DESCRIPTION

Illustrative aspects of the invention will be described in detail with reference to the accompanying drawings.

First, the general structure of an illustrative color laser printer1will be described below.

InFIG. 1, the color laser printer1is a tandem color laser printer in which drum sub units28are arranged in tandem in a horizontal direction. The color laser printer1includes, in a body casing2, a sheet supply section4that supplies a sheet3, an image forming section5that forms an image on the sheet3fed therein, and a sheet ejection section6that ejects the sheet3on which the image is formed.

In the following description, the right side inFIG. 1is referred to as the front side of the printer1, and an opposite side (the left side inFIG. 1) is referred to as the rear side of the printer1, as shown in arrows inFIG. 1. The right and left sides of the printer1are defined when the printer1is viewed from the front side. More specifically, the left and right sides of the printer1are front and rear sides, respectively, in a direction perpendicular to the sheet ofFIG. 1. The left-right direction may be referred to as a width direction.

The body casing2is substantially box shaped in side view. The body casing2has a drum accommodating space7for accommodating a drum unit26, which will be described in detail below.

An opening8that communicates with the drum accommodating space7is provided at the front side of the body casing2. A front cover9to cover or uncover the opening8is disposed at the front side. The front cover9is configured that it is inclined frontward of the body casing2to uncover the opening8, and it is in an upright position along the front face of the body casing2to cover the opening8. With the opening8being uncovered, the drum unit26can be inserted in or removed from the drum accommodating space7through the opening8.

The sheet supply section4is provided at a bottom portion of the body casing2. The sheet supply section4includes a sheet supply tray10, a separation roller11, a separation pad12, a pickup roller13, and a sheet supply path14. The sheet supply tray10holds sheets3therein. The separation roller11and the separation pad12are disposed at the upper front end of the sheet supply tray10to face each other. The pickup roller13is disposed behind the separation roller11. The sheets3are fed along the sheet supply path14.

The sheet supply path14is substantially U shaped in a side view. An upstream end of the sheet supply path14in a sheet feeding direction is disposed near the separation roller11. A downstream end of the sheet supply path14is disposed near a front side of a conveyor belt58(described below). A sheet dust removing roller15and a pinch roller16facing each other are disposed in front of and above the separation roller11in the sheet supply path14. A pair of register rollers17is disposed above the sheet dust removing roller15and the pinch roller16.

The image forming section5includes a scanner unit20, a process unit21, a transfer unit22, and a fixing unit23.

The scanner unit20is disposed in an upper portion of the body casing2. The scanner unit20includes a support plate24extending in the front-rear and right-left directions, and an exposure unit25fixed on the upper surface of the support plate24.

The process unit21is disposed below the scanner unit20and above the sheet supply section4. The process unit21includes a drum unit26, functioning as a photosensitive member unit, and four developing cartridges27for each color, functioning as developer supply units.

The drum unit26includes four drum sub units28. That is, the drum sub units28include a black drum sub unit28K, a yellow drum sub unit28Y, a magenta drum sub unit28M, and a cyan drum sub unit28C.

The drum sub units28are arranged in a row with some distance between adjacent drum sub units28in the front-rear direction. More specifically, the black drum sub unit28K, the yellow drum sub unit28Y, the magenta drum sub unit28M, and the cyan drum sub unit28C, are arranged in this order from the front to the rear.

Each drum sub unit28includes a pair of side frames104and a center frame105disposed between the side frames104. (Refer toFIG. 4.)

As shown inFIG. 2, each drum sub unit28holds a photosensitive drum29, functioning as a photosensitive member, a scorotron charger30, and a cleaning brush31.

The photosensitive drum29includes a drum body32and a drum shaft33. The drum body32extends along the right-left direction and has a cylindrical shape. The outermost layer of the drum body32is coated with a positively charged photosensitive layer formed from polycarbonate. The drum shaft33is disposed along an axial direction of the drum body33. The drum body32is rotatably supported by the drum shaft33. The drum shaft33is inserted into the pair of side frames104(FIG. 4) and is supported by a pair of side plates103(FIG. 4).

The scorotron charger30is disposed behind and diagonally above the photosensitive drum29to face the photosensitive drum29. The scorotron charger30is held by the center frame105. The scorotron charger30includes a charging wire34and a grid35. The scorotron charger30is configured to positively and uniformly charge the surface of the photosensitive drum29while controlling the amount of charge applied to the photosensitive drum29.

The cleaning brush31is disposed in contact with the photosensitive drum29to remove paper dust or fibers on the photosensitive drum29. The cleaning brush31is supported by the center frame105.

The four developing cartridges27are configured to be detachably mounted in the corresponding drum sub units28provided for each color, as shown inFIG. 1. That is, the developing cartridges27includes a black developing cartridge27K detachably mountable in the black drum sub unit28K, a yellow developing cartridge27Y detachably mountable in the yellow drum sub unit28Y, a magenta developing cartridge27M detachably mountable in the magenta drum sub unit28M, and a cyan developing cartridge27C detachably mountable in the cyan drum sub unit28C.

As shown inFIG. 2, each developing cartridge27includes a developing frame36, and an agitator37, a supply roller38, a developing roller39, functioning as a developer carrier, and a layer thickness regulating blade40that are disposed in the developing frame36.

The black developing cartridge27K contains black toner, the yellow developing cartridge27Y contains yellow toner, the magenta developing cartridge27M contains magenta toner, and the cyan developing cartridge27C contains cyan toner. Each developing cartridge27contains, for example, positively chargeable non-magnetic single component polymerized toner.

The transfer unit22is disposed above the sheet supply section4and below the process unit21in the body casing2, along the front-rear direction, as shown inFIG. 1. The transfer unit22includes a drive roller56, a driven roller57, a conveyor belt58, transfer rollers59, and a cleaning unit60.

The sheet3supplied from the sheet supply section4is fed from the front to the rear by the conveyor belt58, which is circulated by the drive roller56and the driven roller57, so as to sequentially pass transfer positions between the conveyor belt58and the photosensitive drums29of the drum sub units28. While the sheet3is being fed, each of the different colored toner images carried on the photosensitive drums29of the drum sub units28are sequentially transferred on top of each other on the sheet3. Thus, a multi-color image is formed on the sheet3.

More specifically, when a black toner image carried on the photosensitive drum29of the black drum sub unit28K is transferred to the sheet3, a yellow toner image formed on the photosensitive drum29of the yellow drum sub unit28Y is then transferred onto the sheet3having the black toner image transferred thereon. Similarly, a magenta toner image formed on the photosensitive drum29of the magenta drum sub unit28M and a cyan toner image formed on the photosensitive drum29of the cyan drum sub unit28C are transferred and laid on top of each other on the sheet3. Thus, a multi-color image is formed on the sheet3.

In the cleaning unit60, during the above toner image transfer, toner adhering to the surface of the conveyor belt58is transferred to a first cleaning roller61and then a second cleaning roller62. The toner transferred to the second cleaning roller62is scraped off by a scraper blade63, and is stored in a toner storing portion64.

The fixing unit23is disposed behind the black drum sub unit28K in the body casing2to face, in the front-rear direction, the transfer position between photosensitive drum29and the conveyor belt58. The fixing unit23includes a heat roller65and a pressure roller66.

The sheet3is fed to the fixing unit23where the color toner image transferred on the sheet3is thermally fixed while the sheet3passes between the heat roller65and the pressure roller66.

In the sheet ejection section6, the sheet3is fed from the fixing unit23along a sheet ejection path67to a feed roller69and a pinch roller70, and ejected by ejection rollers71onto a sheet ejection tray68.

The drum unit26will be described below.

As shown inFIG. 3, the drum unit26includes four drum sub units28for the four colors, a front beam101and a rear beam102, which are disposed in front of and behind the four drum sub unit28, respectively, and a pair of side plates103that sandwich the front beam101, the four drum sub units28, and the rear beam102from each side in a width direction of the drum unit26.

The drum unit26is configured to be slidably installed in or removed from the drum accommodating space7(FIG. 1) in the body casing2together with the four drum sub unit28, the front beam101, the rear beam102, and the pair of side plates103of the drum unit26.

As shown inFIG. 4, each drum sub unit28includes a pair of side frames104disposed to face each other with some distance therebetween in the longitudinal direction of the drum sub unit28(i.e., width direction of the drum unit26/right-left direction), and a center frame105disposed between the side frames104.

Each side frame104is formed of a resin material into a substantially flat plate-like shape. The drum shaft33of the photosensitive drum29is inserted into each side frame104.

Each side frame104has a guide groove106for guiding the developing cartridge27into the corresponding drum sub unit28. Each guide groove106is formed in a substantially top-bottom direction from an upper end at the rear side of the side frame104to a bottom end at the front side of the side frame104. The bottom end (the deepest portion) of each guide groove106is provided at a position corresponding to a position of the developing roller shaft51when the developing roller39is brought into contact with the corresponding photosensitive drum29. Each collar member77of the developing roller shaft51is slidably received in the guide groove106.

Each side frame104is formed with a boss107. The boss107is formed in a tubular shape and protrudes outwardly, in the width direction, from each side frame104. The boss107is disposed at a position corresponding to a window78of the developing cartridge27when the developing cartridge27is mounted in the drum sub unit28.

Each left side frame104is formed with a coupling inside insertion hole109at a position corresponding to a coupling passive gear80of the developing cartridge27in the width direction. The coupling inside insertion hole109is formed as a round hole passing through the left side frame104in its thickness direction.

The center frame105is made of a resin material. The center frame105is provided with support rollers110at both end portions in the width direction of the center frame105. The support rollers110are rotatably supported to a rotating shaft (not shown) extending along the center frame105in the width direction.

The front beam101is made of a resin material as one body. The front beam101is disposed in front of the four drum sub units28arranged in the front-back direction and extended between the side plates103.

The front beam101includes a front handle portion111functioning as a gripping portion and a support shaft112. The front handle portion111is attached to the front beam101in the middle thereof in the width direction. The support shaft112is configured to rotatably support the front handle portion111.

The front handle portion111is substantially U shaped, and is rotatably supported at free ends thereof to the support shaft112. The front handle portion111is movable between a storage position (FIG. 3) where it stands along the front beam101and an operative position (FIG. 4) where it leans to front of the front beam101.

The support shaft112is disposed to pass through the front beam101along the width direction, and is supported by the front beam101. Both end portions of the support shaft112protrude outwardly from the front beam101and the side plates103in the width direction.

The rear beam102is made of a resin material as one body. The rear beam102is disposed behind the four drum sub units28arranged in the front-back direction, and extended between the side plates103.

The rear beam102is formed in substantially an open rear box shape in a top view, and is integrally formed with a rear handle portion113, functioning as a gripping portion, in the middle in the width direction as shown inFIG. 3. The rear handle portion113is substantially U shaped in a rear view, and is connected at free ends thereof to the rear beam102. The rear handle portion113inclines from the lower rear side to the upper front side, and protrudes diagonally upward from the rear beam102.

Each side plate103is made of a material, such as metal and fiber reinforced resin, having higher rigidity than a resin material of the front beam101and the rear beam102. Each side plate103may be made from a thin steel plate.

Each side plate103is a substantially rectangular shape in a side view extending in the front-rear direction. Each side plate103is fixed to the front beam101, the four drum sub units28, and the rear beam102, so as to face the front beam101at its front end and the rear beam102at its rear end.

Each side plate103is formed with a flanged portion114, which is bent outward in the width direction from an upper end the side plate103so as to form a substantially L shape in a cross sectional view. The flanged portion114extends in a straight manner along the front-rear direction.

The rear end of each side plate103extends rearward at its upper portion so that it is substantially L shaped in a side view. Two roller members118are rotatably disposed in the upper portion of the rear end of each side plate103extending rearward. The two roller members118may be designed to have a dimension (e.g., thickness) in the width direction of the drum unit26substantially equal to a dimension in the width direction of the flanged portion114, and are disposed to sandwich the spacer119therebetween in the front-rear direction. The front-side roller member118F is disposed under the flanged portion114and the rear-side roller member118R is disposed behind the rear end portion of the flanged portion114. Each roller member118has an outer diameter defined as A. As each side plate103is formed in a thin plate-like shaped manner as described above, the outer diameter A of the front-side roller member118F includes the thickness of the flanged portion114which is adjacent to the upper portion of the roller member118F. In other words, a length from a bottom end of the roller member118F to the upper end of the flanged portion114which is adjacent to the upper portion of the roller member118F is defined as A.

The rear end of each side plate103is formed with a cutout portion120that is a substantially U shaped cut out in a side view. The cutout portion120is configured to receive a positioning shaft (not shown), which is disposed in the body casing2, when the drum unit26is mounted in the body casing2. Thus, the drum unit26is positioned in the body casing2.

Each side plate103is formed at its upper end portion with four light transmission holes115, which are spaced at intervals in the front-rear direction. Each light transmission hole115is configured to receive the boss107of each drum sub unit28. Each light transmission hole115is formed as a round hole passing through the side plate103in its thickness direction at a position facing the boss107of the drum sub unit28in the width direction. The boss107of each drum sub unit28is engaged in each light transmission hole115so as to become exposed outwardly in the width direction. This controls the rotation of each drum sub unit28on the drum shaft33with respect to each side plate103.

Each side plate103is formed at its lower end portion with shaft holes116in which axial ends of each drum shaft33are inserted.

The left side plate103is formed with four coupling outside insertion holes117, which are spaced at intervals along the front-rear direction at a middle portion in the vertical direction. Each coupling outside insertion hole117is configured to face the coupling passive gear80of each developing cartridge27in the width direction when the developing cartridge27is mounted in the drum unit26. Each coupling outside insertion hole117is formed as a round hole passing the side plate103in its thickness direction at a position facing the coupling inside insertion hole109of each drum sub unit28.

A structure of each developing cartridge27will be described below.

As shown inFIG. 5, the developing frame36of each developing cartridge27integrally includes a pair of sidewalls73, a top wall74, a front wall75, and a rear wall76. The top wall74is disposed between the sidewalls73at their top ends. The front wall75is disposed between the sidewalls73at their front ends. The rear wall76is disposed between the sidewalls73at their rear ends. The sidewalls73, the front wall75, and the rear wall76define the opening41, at their bottom ends, from which the developing roller39is exposed.

Windows78for detecting the amount of toner stored in the toner chamber43(FIG. 2) are embedded in both sidewalls73. The windows78are disposed oppositely to each other across the toner chamber43. The windows78allow light to pass therethrough along the width direction for detecting the amount of toner.

The left sidewall73is provided with a gear mechanism (not shown) covered with a gear cover79. The coupling passive gear80is disposed in the lower end portion of the gear cover79so as to become exposed from the outside surface of the gear cover79.

A coupling shaft (not shown) provided in the body casing2is coupled to the coupling passive gear80so as to advance or retract and rotate together with the coupling passive gear80. The coupling passive gear80receives a drive force from a motor (not shown) provided in the body casing2via the coupling shaft. The drive force transmitted to the coupling passive gear80is transmitted to the agitator37, the supply roller38, and the developing roller39via the gear mechanism.

The developing roller shaft51is rotatably supported in the developing fame36. The left end of the developing roller shaft51protrudes outward from the gear cover79, and the right end protrudes outward from the right side wall73. The left end and right end of the developing roller shaft51are covered with collar members77.

Both sidewalls73of the developing frame36have separation protrusions83in their upper rear portions. The separation protrusions83are formed in cylindrical hollow members protruding outward from both sidewalls73.

The developing frame36is provided with a handle84. The handle84is formed in a thin plate-like shape elongated in the width direction, and is disposed on the top wall74of the developing frame36.

A rotating shaft (not shown) is inserted into the handle84at its rear end along the right-left direction. The handle84is pivotally supported via the rotating shaft at the rear end of the top wall74of the developing frame36.

The handle84is formed with an elongated hole85having a substantially rectangular shape in the middle in the width direction. A user inserts his/her fingers into the elongated hole85to hold the handle84.

The handle84and the top wall74are coupled, at their right and left ends of their front ends, with elastic members such as coil springs, plate springs, and sponges. The front end of the handle84is normally urged in a direction to separate from the front end of the top wall74.

The handle84is formed with pressing protrusions82at the right and left ends of the front end. The pressing protrusions82protrude outwardly in the width direction.

As shown inFIG. 2, the front wall75is formed with a supported protrusion86at each of the right and left ends in the width direction. The supported protrusion86has a substantially trapezoidal shape in a side view, and protrudes frontward.

Installation and removal of the developing cartridge27from the drum unit26will be described below.

As shown inFIG. 4, the developing cartridge27for each color is inserted into the corresponding drum sub unit28of the drum unit26from above by a user who inserts his/her finger into the elongated hole85and holds the handle84.

More specifically, the collar members77covering both ends of the developing roller shaft51of the developing cartridge27are inserted into guide grooves106formed in the side frames104of the drum sub unit28and the developing cartridge27is pressed downward in the drum sub unit28along the guide grooves106. When the developing roller39contacts the photosensitive drum29, the developing cartridge27is regulated so as not to be pressed further downward. The developing cartridge27tilts or pivots about the developing roller shaft51under its own weight in a direction that the upper end of the developing cartridge27leans to the adjacent center frame105disposed in front of the inserted developing cartridge27. Each supported protrusion86formed at the front wall75of the developing frame36is brought into contact with and supported by the corresponding support roller110of the center frame105. Thus, the developing cartridge27is installed in position in the drum sub unit28.

When all developing cartridges27are installed in the corresponding drum sub units28as shown inFIG. 3, the front handle portion111of the front beam101, the handles84of all developing cartridges27, and the rear handle portion113of the rear beam103are arranged so that they overlap each other in the front-rear direction.

When a user holds and raises the handle84of a developing cartridge27installed in the drum unit26(the drum sub unit28), the developing cartridge27can be removed from the drum unit26.

A structure of the body casing2will be described below.

As shown inFIG. 6, the body casing2includes a pair of body frames123disposed oppositely to each other across the drum unit26. The body frames123function as guide walls. Each body frame123includes a rail124, a control portion121, and a separation pressing mechanism125on its inside surface. The rail124is configured to guide the drum unit26during installation and removal. The control portion121is configured to control the movement of the drum unit26into or out of the body casing2. The separation/pressing mechanism125is configured to separate or press the developing roller39of the developing cartridge27installed in the drum unit26from or against the corresponding photosensitive drum29.

As shown inFIG. 6, the rails124of the respective body frames123are disposed oppositely to each other across the drum unit26in the width direction. Each rail124includes a rail fixing portion126disposed at a front end of the body frame123, a rail main body127extending along the inside surface of the body frame123, a rail connection portion128configured to connect the rail fixing portion126and the rail main body127, and a roller storage portion132(FIG. 7) disposed in contact with a rear end of the rail main body127.

The rail fixing portions126are fixed to the front end surfaces of the respective body frames123.

Each rail main body127is substantially L shaped in a front view where its bottom end is bent inward in the width direction as shown inFIG. 7. The bottom end, which is defined as a flat portion131, extends in the width direction. The flanged portion114(FIG. 3) of each side plate103of the drum unit26installed in the body casing2is disposed on the flat portion131from above. The flat portion131can have a dimension in the width direction slightly longer than a dimension in the width direction of the flanged portion114and the roller member118(FIG. 3).

Each rail connection portion128is formed to connect an inside end of the rail fixing portion126and a front end of the rail main body127, as shown inFIG. 6. As shown inFIG. 7, roller shafts129are inserted and supported in the corresponding rail connection portions128in the width direction. Rail rollers130are rotatably supported around the corresponding roller shaft129and disposed on inside surfaces of the rail connection portions128in the width direction so as to face each other. The rail rollers130are configured to have a dimension (thickness) in the width direction substantially equal to the dimension (width) in the width direction of the flat portion131of each rail main body127, and are spaced with a distance substantially equal to that between the right and left rail rollers118(FIG. 3) of the drum unit26. As shown inFIG. 7, each rail roller130is disposed such that a top end of its circumferential surface is higher than the flat portion131of the rail main body127.

A protrusion122is substantially triangular in a side view and is provided between the rail roller130and the rail main body127. The protrusion122is formed such that two sides of the triangle are tangent to each rail roller130and the two sides converge slightly before the front end of the flat portion131. With this configuration, the top end of the circumferential surface of the rail roller130, an upper surface of the protrusion122, and an upper surface of the flat portion131continue.

The roller storage portion132is formed in a substantiallyFIG. 8shape where a substantially triangular portion and a substantially square portion are connected at their respective one vertex in a side view. The substantially triangular portion is connected to a rear end of the flat portion131, and the substantially square portion is disposed diagonally rearward behind the substantially triangular portion. The roller storage portion132is formed at its upper surface with an inclined surface136continuing from the rear end of the flat portion131and extending diagonally rearward and downward. The inclined surface136includes a recessed portion137at a connection portion of the substantially triangular portion and the substantially square portion of the roller storage portion132. The recessed portion137is recessed diagonally frontward and downward. The inclined surface136extends horizontally in the front-rear direction rearward from the recessed portion137. The roller storage portion132has a dimension (thickness) in the width direction substantially equal to the dimension (width) in the width direction of the flat portion131.

As shown inFIG. 6, the control portion121is disposed above the rail connection portion128in each body frame123. Each control portion121includes a rotation support shaft88and a control member89. Each control portion121is connected with a rotation connection portion90(FIG. 7).

The rotation support shaft88protrudes inward in the width direction from the inside surface of each body frame123.

As shown inFIG. 7, the control members89of the respective control portions121are disposed opposite to each other in the width direction. The control members89are spaced with a distance substantially equal to that between the rail rollers130in the width direction. In a side view, the left control member89L is formed in the shape of an inverse T, and the right control member89R is substantially L-shaped. Each control member89integrally includes an insertion portion92, a joining portion96, and an interference portion97, in this order from above.

The insertion portion92is formed in a hollow cylindrical shape elongated in the width direction. The rotation support shaft88is rotatably supported in the insertion portion92, so that the control member89is rotatably supported in the body frame123(FIG. 6).

The insertion portion92is formed with a gear portion93on a peripheral surface of the outer half side of the insertion portion92in the width direction.

The joining portion96is formed in a thin plate-like shape extending in a direction outwardly, in a radial direction of the insertion portion92, from a substantially central portion of the insertion portion92in the width direction.

The interference portion97is connected to an end of the joining portion96opposite from another end thereof connected to the insertion portion92. The interference portion97is substantially rectangularly shaped, in a side view, and protrudes inward more than the joining portion96in the width direction. The interference portion97has a dimension in the width direction slightly longer than the dimension in the width direction of the corresponding rail roller130. The interference portion97may be slightly thicker than the rail roller130.

An interference portion97L of the left control member89L is connected to the joining portion96so that a front end of the interference portion97L is positioned frontward more than the joining portion96, and a rear end of the interference portion97L is positioned rearward more than the joining portion96. The interference portion97L is formed with a recessed portion98that recesses leftward from the right side surface.

An interference portion97R of the right control member89R is connected to the corresponding joining portion96so that a front surface of the interference portion97R is flush with the front surface of the joining portion96and a rear end of the interference portion97R is positioned rearward more than the joining portion96.

The rear end of each interference portion97is formed in a hook shape in a side view, and thus is referred to as a hook91.

The rotation connection portion90is disposed diagonally behind and above the control members89and includes a connection shaft94and connection gears95.

The connection shaft94is rotatably supported between the body frames123(FIG. 6), and the connection gears95are fitted around both ends of the connection shaft94so as to rotate together with the connection shaft94.

Each connection gear95is engaged with a corresponding one of gear portions93of the control members89. When the user puts his/her finger into the recessed portion98of the left control member89L and actuates the left control member89L, the force applied to the left control member89L is transmitted to the gear portion93of the left control member89L, the rotation connection member90, the right control member89R, and the gear portion93of the right control member89R, in this order. Thus, the left control member89L and the right control member89R rotate together.

Each control member89is capable of rotating between a holding position (FIG. 7) and a release position (FIG. 8). In the holding position, each interference portion97is positioned at a substantially 6 o'clock position in a right side view, and each hook91engages with the front end of the corresponding separation/pressing mechanism125. In the release position, each interference portion97is positioned at a substantially 8 o'clock position in a right side view. Each interference portion97faces the corresponding rail roller130vertically both in the holding position and the release position.

Each separation/pressing mechanism125is disposed adjacent to the rail main body127from above and the control member89placed in the holding position from the rear. Each separation/pressing mechanism125integrally includes a fixing portion133and a receiving portion134. Each separation/pressing mechanism125is elongated in the front-rear direction and formed in a substantially inverse P shape in a front cross sectional view.

The fixing portion133is formed in a thin plate-like shape, and includes screw holes135disposed in the front-rear direction. Screws (not shown) are inserted and tightened in the screw holes135of the fixing portion133, so that the separation/pressing mechanism125is fixed to the body frame123.

The receiving portion134is substantially U shaped and recesses inward in the width direction in a front cross sectional view. The receiving portion134integrally includes a top surface portion138, a side surface portion139, and a bottom surface portion140, which form its front cross sectional shape.

The top surface portion138is disposed so that it is continuous with an upper surface of the interference portion97of the control member89placed in the holding position. An outer edge of the top surface portion138in the width direction is connected to a bottom edge of the fixing portion133. The top surface portion138extends inward in the width direction.

The bottom surface portion140is connected to a bottom end of the side surface portion139and extends outward in the width direction. An outer edge of the bottom surface portion140in the width direction is connected to an upper edge of the rail main body127. The bottom surface portion140vertically faces the flat portion131of the rail main body127. A front edge of the bottom surface portion140has an inclined portion99that inclines from the lower bottom to the upper front.

The separation/pressing mechanism125has four first cutout portions141provided at equal intervals along the front-rear direction. Each first cutout portion141is provided extending from the outer edge of the top surface portion138to a lower portion of the side surface portion139. The first cutout portions141are sized to be capable of receiving the pressing protrusions82(FIG. 5) of the corresponding developing cartridges27.

Four second cutout portions142are formed at the rear of the corresponding first cutout portions141. Each second cutout portion142is provided extending from the outer edge of the top surface portion138to a substantially vertically central portion of the side surface portion139. The second cutout portions142are formed to a size capable of receiving the separation protrusions83(FIG. 5) of the corresponding developing cartridges27.

In each body frame123of the body casing2, there is a space vertically defined by the bottom surface portion140of the separation/pressing mechanism125, the control member89of the control portion121, the flat portion131of the rail124, the inclined surface136of the roller storage portion132, and the rail roller130and the protrusion122in the rail connection portion128. This space provides a guide region143for guiding the drum unit26when it is attached to and removed from the body casing2. When the drum unit26is attached to or removed from the body casing2, the roller members118(FIG. 3) and the flanged portions114can be slid in the guide regions143.

A dimension (height) of the guide region143at its front end is the shortest distance between the control member89and the rail roller130. A shortest distance B between the control member89placed in the holding position and the rail roller130is set smaller than an outer diameter A of the roller member118(FIG. 3) of the drum unit26. As shown inFIG. 8, a shortest distance C between the control member89placed in the release position and the rail roller130is set greater than the outer diameter A of the roller member118.

In each guide region143, a shortest distance D between a front end of the inclined portion99of the bottom surface portion140of the separation/pressing mechanism125and the flat portion131of the rail124is set greater than the outer diameter A of the roller member118. A shortest distance E between a rear end of the inclined portion99and the flat portion131is smaller than the shortest distance D but is set greater than the outer diameter A of the roller member118. A distance between the flat portion131and the bottom surface portion140except for the inclined portion99is set constantly with the distance E.

Installation of the drum unit26in the body casing2will be described in detail with reference toFIGS. 1,3and9through17.

To attach the drum unit26to the body casing2, the front handle portion111(FIG. 3) and the rear handle portion113(FIG. 3) of the drum unit26are held and raised with both hands. The front cover9(FIG. 1) is tilted down to uncover the opening8, the control members89are rotated to the release position (FIG. 9), and the drum unit26is inserted into drum accommodating space7from front to rear. When the drum unit26is installed in the drum accommodating space7of the body casing2, the drum unit26is placed in a first position.

As shown inFIG. 9, the shortest distance C between the control member89placed in the release position and the rail roller130is greater than the outer diameter A of the roller member118. Thus, when the drum unit26is inserted into the drum accommodating space7of the body casing2, the roller member118R can pass in between the control member89and the rail roller130, enter the guide region143, and move over the rail roller130. InFIG. 9, the roller member118R moves past the rail roller130, and the spacer119moves on top of the rail roller130.

When the drum unit26is inserted further rearward as it is held in a posture shown inFIG. 9, the roller member118R contacts the front end of the inclined portion99of the bottom surface portion140of the separation/pressing mechanism125as shown inFIG. 10. As described above, the shortest distance D between the front end of the inclined portion99and the flat portion131of the rail124is greater than the outer diameter A of the roller member118. Thus, the roller member118R can move rearward in the guide region143.

When the drum unit26is inserted further, the roller member118R is guided by the inclined portion99of the bottom surface portion140, and approaches the rear end of the inclined portion99as shown inFIG. 11. Accordingly, the drum unit26is inclined with its front end placed higher than its rear end. At this time, the roller member118F moves on top of the rail roller130. As described above, the shortest distance E between the rear end of the inclined portion99of the bottom surface portion140and the flat portion131is greater than the outer diameter A of the roller member118. Thus, the roller member118R can move further rearward in the guide region143.

When the drum unit26is inserted further rearward, the roller member118F moves past the rail roller130and the protrusion122, and the roller members118F and118R are disposed on top of the flat portion131, as shown inFIG. 12. At this time, the drum unit26is placed in a second position. When the drum unit26is placed in the second position, all developing cartridges27installed in the drum unit26are exposed, and the developing cartridges27can be removed from the drum unit26.

In this situation, when the user releases the front handle portion111and the rear handle portion113, the drum unit26can be moved from the current position where the front end is positioned higher than the rear end to a position shown inFIG. 13where the front end is level with the rear end. At this time, the rail roller130contacts the bottom surface of the flanged portion114, the roller member118F contacts the upper surface of the flat portion131, and the roller member118R contacts the bottom surface of the bottom surface portion140, so that the drum unit26is supported by the body casing2. Unless the roller members118F and118R move frontward over the rail roller130, the drum unit26can not be separated from the body casing2. In a situation shown inFIG. 13, the drum unit26does not fall off the body casing2even if the user releases the front handle portion111and the rear handle portion113.

When the user holds the front handle portion111and inserts the drum unit26further rearward, the interference portion97of each control member89placed in the release position contacts the corresponding separation protrusion83of the developing cartridge27C arranged at the most rear side in the drum unit26, and the drum unit26is prevented from moving further rearward.

Thus, as shown inFIG. 14, when the control member89is rotated to the holding position, the corresponding separation protrusion83is allowed to pass the inner space between the interference portion97and the insertion portion92of the control member89, that is the inner side of the joining portion96(FIG. 7) of the control member89, in the width direction, and thus the drum unit26is allowed to move rearward.

When the drum unit26is inserted further rearward, each roller member118rotates on the flat portion131of the rail main body127while the flanged portion114slides on the rail roller130. In this way, the drum unit26smoothly moves. The separation protrusions83and pressing protrusions82of each developing cartridge27slide on the upper surface portion138of each separation/pressing mechanism125.

When the drum unit26is inserted further rearward, each roller member118drops off the rear end of the flat portion131, the flanged portion114drops off the rail roller130and is placed above the flat portion131as shown inFIG. 15. At this time, the roller member118F is engaged in the recessed portion137of the roller storage portion132. In each developing cartridge27, each pressing protrusion82is received in the corresponding first cutout portion141of the separation/pressing mechanism125, and each separation protrusion83is received in the corresponding second cutout portion142. Thus, the drum unit26is completely installed in the body casing2. At this time, the drum unit26is placed in the first position.

Then, the user releases the front handle portion111and closes the front cover9(FIG. 1) to cover the opening8(FIG. 1).

In each separation/pressing mechanism125, a pressing mechanism (not shown) is provided in each first cutout portion141, and a separation mechanism (not shown) is provided in each second cutout portion142. In a state where the drum unit26is installed in the body casing2as shown inFIG. 1, the color laser printer1can form a color image using the four drum sub units28and a monochrome image using the black drum sub unit28only, selectively according to the user's purpose.

Specifically, the user operates an operation panel (not shown), and selects whether an image is formed in color or monochrome. When an image is formed in color, the pressing mechanism (not shown) applies downward force to the pressing protrusions82(FIG. 5) of the four developing cartridges27. The front end of the handle84including the pressing protrusions82moves to the front end of the top wall74of the developing frame36against an urging force of an elastic member (not shown) provided in the handle84. Along with the movement, the urging force of the elastic member (not shown) acts on the front end of the top wall74in a direction to separate from the front end of the handle84(downwardly). Thus, each developing frame36of the four developing cartridges27moves downward, each developing roller39is pressed against the surface of the corresponding photosensitive drum29as shown inFIG. 1, toner on each developing roller39is supplied to the corresponding photosensitive drum29, and a color image is formed.

When a monochrome image is formed, downward force is applied to the pressing protrusions82(FIG. 5) of the black developing cartridge27K only. In the other developing cartridges27except for the black developing cartridge27K, upward force is applied to the separation protrusions83by the separation mechanism (not shown). Thus, the black developing cartridge27K moves downward, and the developing roller39of the black developing cartridge27K is pressed against the surface of the photosensitive drum29of the black drum sub unit28K. On the other hand, the other developing cartridges27except for the black developing cartridge27K move upward, and their developing rollers39are separated from the corresponding photosensitive drums29. Thus, toner on the developing cartridge39of the black developing cartridge27K only is applied to the photosensitive drum29of the black drum sub unit28K, and a monochrome image is formed.

Removal of the drum unit26from the body casing2will be described below.

When the drum unit26is removed from the body casing2, the front cover9(FIG. 1) is tilted to uncover the opening8, the front handle portion111(FIG. 16) is held, and the drum unit26is pulled frontward. At this time, the roller member118F in the drum unit26is removed from the recessed portion137of the roller storage portion132, guided along the inclined surface136of the roller storage portion132, and moves on the flat portion131of the rail main body127. Each flanged portion114of the drum unit26moves on top of the corresponding rail roller130. The pressing protrusions82and the separation protrusions83of each developing cartridge27are separated from the corresponding first output portions141and second output portions142diagonally upward and frontward.

When each control member89is placed in the release position, the hook91engages with the corresponding separation protrusion83of the black developing cartridge27K disposed at the front of the drum unit26, so that the drum unit26is prevented from moving further forward.

When the control member89is rotated to the holding position as shown inFIG. 17, the corresponding separation protrusion83is allowed to pass the inner space between the interference portion97and the insertion portion92of the control member89, that is the inner side of the joining portion96of the control member89, in the width direction, and thus the drum unit26is allowed to move frontward.

When the roller member118F of the drum unit26contacts the protrusion122of the rail connection portion128, the drum unit26is placed in the second position, and the drum unit26is stopped from moving frontward. The interference portion97of the control member89contacts the upper surface of the flanged portion114of the drum unit26. The shortest distance B between the control member89and the rail roller130is smaller than the outer diameter A of the roller member118F (which includes the thickness of the flanged portion114adjacent to the roller member118F), as described above. Thus, the roller member118F can not move over the protrusion122and the rail roller130, and the drum unit26can not be separated from the body casing2.

However, as the control member89is rotated to the release position, the roller members118F and118R can move over the protrusion122and the rail roller130as shown inFIGS. 9 and 11. In the drum unit26placed in the second position, the rear handle portion113is exposed outside and can be operated. Thus, the user can grasp the front handle portion111and the rear handle portion113again with both hands to pull the drum unit26out frontward. As shown inFIG. 9, the roller member118R passes frontward between the control member89placed in the release position and the rail roller130, and the roller member118and the flanged portion114disengaged from the guide region143, so that the drum unit26is completely removed from the body casing2. At this time, the drum unit26is placed in a third position.

In the laser printer1, the dimension (height) of the guide region143at the most downstream side in the direction where the drum unit26is pulled out from the body casing2, in other words, the dimension of the guide region143at its front end, is the shortest distance between the control member89and the rail roller130. When the control member89is placed in the holding position, the shortest distance is maintained with B (second guide region dimension) which is smaller than the outside diameter A of the roller member118of the drum unit26. When the control member89is placed in the release position, the shortest distance between the control member89and the rail roller130is extended to C (third guide region dimension) which is greater than the outside diameter A of the roller member118. In the guide region143, the dimension of the guide region in a portion rearward from the front end, that is, the dimension of the guide region between the bottom surface portion140of each separation/pressing mechanism125and the flat portion131of the rail124, is defined as D or E (first guide region dimension) which is greater than the outside diameter A of the roller member118.

Thus, when the drum unit26is installed in or removed from the body casing2, the roller member118is guided in a portion where the first guide region dimension is formed in the guide region143, the drum unit26can smoothly move between the first position and the second position.

However, unless the control member89is placed in the release position even if the drum unit26is withdrawn to the second position, the roller member118can not pass in between the control member89and the rail roller130, and the drum unit26can not move to the third position. Thus, when the control member89is placed in the holding position, the drum unit26can be surely controlled in its movement between the first position and the second position. When the drum unit26is placed in the second position, the user can hold the drum unit26before the control member89is moved to the release position, and the drum unit26can be removed from the body casing2with a stable posture simply and surely. To hold the drum unit26removed from the body casing2again, there is no need to provide the apparatus with a member for temporarily placing the drum unit26, and thus the apparatus can be smaller in size.

When the control member89is placed in the release position, the roller member118of the drum unit26can pass in between the control member89and the rail roller130, and the drum unit26can be moved between the second position and the third position surely.

When the control member89is placed in the release position and the drum unit26in the second position is pressed rearward toward the first position, the interference portion97of each control member89in the release position contacts the corresponding separation protrusion83of the developing cartridge27C disposed at the rear end of the drum unit26, and the drum unit26is controlled from moving further rearward. When the drum unit26placed in the first position is pulled frontward toward the second position, the hook91of each control member89in the release position engages with the corresponding separation protrusion83of the developing cartridge27K disposed at the front end of the drum unit26, and the drum unit26is controlled from moving further forward.

Thus, with the control member89being placed in the release position, the drum unit26is controlled in its movement between the first position and the second position. When the drum unit26is placed in the first position, it can be controlled from unnecessarily moving toward the second position. That is, the drum unit26can be prevented from moving from the first position directly to the third position without stop. When the drum unit26is placed in the second position, it can be controlled from unnecessarily moving toward the first position. That is, in a state where the control member89is not returned to the holding position, the drum unit26cannot be moved to the first position, and thus can be prevented from moving into the drum accommodating space7.

The drum unit26includes the front handle portion111and the rear handle portion113. With the front handle portion111, the drum unit26in the first position can be easily pulled toward the second position. When the drum unit26is placed in the second position, the rear handle portion113can be operated. When the drum unit26is placed in the second position, all developing cartridges27can be installed in or removed from the drum unit26. Thus, the user can hold the front handle portion111and the rear handle portion113, which are suitable portions of the drum unit26to be held except for the developing cartridges27, and remove the drum unit26from the body casing with a stable posture and easily and securely.

The control members89are rotatably provided at both ends of the body casing2in the width direction, which is perpendicular to a direction where the drum unit26is withdrawn from the body casing2. Thus, the control members89are easily moved between the holding position and the release position, so that the movement of the drum unit26is controlled. The movement of the control members89is implemented only by provision of the rotation support shafts88, thus facilitating a configuration to move the control members89between the holding position and the release position.

The control members89L and89R disposed at both sides of the body casing2in the width direction are rotated together by the rotation connection portion90. Thus, when the control members89are rotated from the holding position to the release position, there is no need to rotate the control members89L and89R independently, thus improving operability.

In the drum unit26according to the above aspect, each developing cartridge27is provided separately from the corresponding drum sub unit28so as to be individually installed in or removed from the corresponding drum sub unit28. However, the developing cartridge27and the drum sub unit28may be integrally formed for each color. In this case, when the drum unit26is replaced with a new one, the toner, the developing roller39, and the photosensitive drum29for each color may be replaced at a time.

In the above embodiment, the color laser printer1illustrated is a tandem-type in which an image is transferred from each photosensitive drum29directly to a sheet3, and is not intended to be limiting. For example, the color laser printer1may be constructed as an intermediate transfer type in which a toner image of each color is transferred from each photosensitive member to an intermediate transfer medium, and then transferred to a sheet at a time. Alternatively, the color laser printer1may be constructed as a monochrome laser printer. The monochrome laser printer may be provided with a process unit functioning as an image formation unit where one developing cartridge27is installed in one drum sub unit28.