Image forming apparatus and developing cartridge having driving input and guide

A system that provides a compact and functional image forming device that can securely supply a driving force to the developing cartridge is described. A developing cartridge is described that can be mounted to the image forming device in an insertable/removable manner. A passive coupling gear and cylinder externally project in the width direction of the collar member allowing secure supply of a driving force through connection of the passive coupling gear to the coupling input shaft. In addition, the amount of movement of the coupling input shaft to connect with the passive coupling gear can be minimized, thereby allowing for a miniaturization of the color laser printer. Furthermore, in addition to the original function, the function of being guided by the left guiding groove for the passive coupling gear and the function of being guided by the right groove for the cylinder can be added.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application Nos. 2006-122215 filed Apr. 26, 2006 and 2005-376119 filed Dec. 27, 2005, the entire contents of which are incorporated herein by reference.

FIELD

Aspects of the present invention relate to an image forming device such as a laser printer and a developing cartridge capable of being used with the image forming device.

BACKGROUND

Color image forming devices are known in which a number of developing cartridges are arranged in line in an insertable/removable manner. These developing cartridges supply toner to the surface of an image carrier of a photoconductor cartridge. The developing cartridges may be arranged in line in an insertable/removable manner. The combination of the image carriers and the developing cartridges and other components can be referred to generally as image forming devices (including but not limited to devices such as laser printers).

In one example of an image forming device, a developing cartridge includes a toner supply. The developing cartridge includes a toner storage and developer carrier that carries the toner. The toner is carried on the surface of a developer carrier. The toner is supplied to a static latent image present on the surface of the image carrier when the developer carrier contacts the surface of the image carrier. This occurs during the rotation of the developer carrier. Accordingly, the static latent image on the surface of the image carrier is developed to an image formed by the developing powder. Next, the developing powder is transferred to paper, resulting in an image in developing powder (or toner) formed on the paper.

In addition, the photoconductor cartridge is insertable to and/or removable from the color image formation device. While the photoconductor cartridge is installed in the color image forming device, a gear on the image carrier is directly engaged with a driving gear that is provided on the color image forming device body.

In at least one example, the developing cartridge is attached to the photoconductor cartridge by a guiding groove. Guiding projections may be provided on both lateral surfaces of the guiding groove. The guiding groove may be formed on a photoconductor cartridge frame. When installed and connected in this manner, a developing bias is applied to the developer carrier so that it carries the toner. The developing bias is provided from an electrode provided on the photoconductor cartridge frame. In addition, a developer carrier gear that is provided on the developer carrier is engaged with the gear of the image carrier. The developer carrier gear may be synchronized with the rotation of the photoconductor gear that is directly engaged to the driving gear. The driving gear may be provided on the body of the color image forming device. By this construction, the developer carrier rotates.

SUMMARY

Aspects of the invention provide an improved developing cartridge that exhibits an improved guiding structure. These and other aspects of the disclosure will be apparent upon consideration of the following detailed description of illustrative embodiments.

DETAILED DESCRIPTION

The various aspects summarized previously may be embodied in various forms. The following description shows by way of illustration of various combinations and configurations in which the aspects may be practiced. It is understood that the described aspects and/or embodiments are merely examples, and that other aspects and/or embodiments may be utilized and structural and functional modifications may be made, without departing from the scope of the present disclosure.

1. THE OVERALL STRUCTURE OF THE COLOR LASER PRINTER

FIG. 1is a lateral cross-sectional view that shows a portion of an embodiment of a color laser printer as an image forming device according to one or more aspects of the present invention.FIG. 2is a lateral cross-sectional view that shows a portion of the drum subunit, in which the developing cartridge is mounted, of the color laser printer shown inFIG. 1.FIG. 3is a lateral cross-sectional view that shows a portion of the developing cartridge shown inFIG. 2.

The color laser printer1shown inFIG. 1is a transverse tandem-type color laser printer in which the multiple drum subunits23that are described in a later section are provided in parallel in the horizontal direction. The color laser printer1may also include a paper feed4that feeds paper3, image formation portion5that forms the image on the fed paper3, and a paper discharge portion6that discharges paper3where an image is formed in the main body casing2. The main body casing2may be an image forming device body.

The color laser1may alternatively include an intermediate image transfer belt (where images from drum subunits23provide developer to an intermediate image transfer belt, that later transfers and image to a print medium) used with drum subunits23or a photosensitive belt that replaces drum subunits23.

In the following explanation, the right side of the paper inFIG. 1(the side in which the drum inserting/removing opening162is formed on the main body casing2) is the front side of the laser printer1, and the left side of the paper inFIG. 1is the rear side of the color laser printer1. In addition, the near side in the direction of the paper thickness inFIG. 1is the left side and the far side in the direction of the paper thickness inFIG. 1is the right side.

Furthermore, unless specifically mentioned, the following directions are the direction in the condition in which the developing cartridge22is installed in the main body casing2.

(1) Paper Feed

Paper feed4is insertable/removable by sliding the paper feed4in the front/rear direction from the front of the tray container171of the main body casing2at the bottom of the main body casing2. Paper feed4includes a paper feed tray7that holds paper3, a separation roller8, separation pad9, and a paper feed roller10. The paper feed tray7, the separation roller8, and the separation pad9are provided so that they face each other at the top front edge of the paper feed tray7. The paper feed roller10is provided next to the separation roller8.

The paper feed side pathway11of paper3is formed in an approximately U-shape. Paper3is fed towards the front. After paper3is flipped, paper3is discharged in a direction toward the rear side of the image forming device. As a result, the upstream edge of paper3is positioned adjacent to the separation roller8at the bottom. Also, the downstream edge of the paper3is positioned adjacent to the feed belt53in the paper feed4.

Paper dust removing roller12and pinch roller16may be provided on the front top of the separation roller8. The paper dust removing roller12and pinch roller16may also face each other. A pair of resist rollers14may be provided on top of paper dust removing roller12and pinch roller13. The paper dust removing roller12, pinch roller13, and the pair of resist rollers14may be provided in the middle of the paper side feed pathway11.

A paper pressing plate15that contacts the layers of paper3may be provided inside the paper feed tray7. The paper pressing plate15may be supported at the rear edge in a movable manner so that the paper pressing plate15can move between a loading position (contacting a floor plate of the paper feed tray7where the front edge portion is positioned at the bottom of the paper feed tray7), and the paper feed position (where the front edge portion of the paper pressing plate15is positioned at the top of the paper feed tray7).

In addition, a lever16is provided at the front edge bottom of the paper feed tray7. Lever16lifts the front edge of the paper pressing plate15upwards. Lever16is supported at the bottom of the front edge of the paper pressing plate15. Lever16moves vertically.

With the movement of the lever16, the front edge of the paper pressing plate15is lifted by the lever16. Also, the paper pressing plate15moves upward into a paper feed position (from which paper is retrieved).

When the paper pressing plate15is positioned at the paper feed position, the paper3at the top on the paper pressing plate15is pressed by the paper feed roller10. Paper3is then fed between the separation roller8and separation pad9by the rotation of the paper feed roller10.

When the paper feed tray7is removed from the main body casing2, the paper pressing plate15is positioned at the loading position. When the paper pressing plate15is positioned at the loading position, the paper3can be loaded in layers on the paper pressing plate15.

Next, the fed paper3is sandwiched between the separation roller8and separation pad9. When the separation roller8rotates, paper3is fed in individual sheets. The fed paper3then passes between the paper dust removing roller12and pinch roller13. Here, paper dust on paper3is then removed. The paper3is then fed along the paper side feed pathway11towards the resist roller14.

The resist roller14temporarily stops the forward movement of paper3. Next, resist roller14rotates and then feeds the paper3to the feed belt53.

(2) Image Forming Portion

The image forming portion5includes a scanner17, a processing unit18, a transfer portion19, and a fixing portion20.

The scanner17is arranged on the top of the main body casing2. Although not shown in the drawing, scanner17may includes a laser emitter, a polygon mirror, multiple lenses, and a reflective mirror (or other known scanner parts). At the scanner17, a laser beam emitted from the laser emitter is based on image data corresponding to each color used in the image forming device1. The laser beam is then reflected by the rotating polygon mirror. The laser then passes through or is reflected by the multiple lenses or reflective mirror. The laser is then output in correspondence to each of the image carriers24relating to the color associated with each image carrier24.

(2-2) Processing Unit

The processing unit18may be positioned below the scanner17and above the paper feed4. The processing unit18may include a drum unit21, and four developing cartridges22(with each developing cartridge22corresponding to one of the toner colors in the image forming device1, respectfully).

(2-2-1) Drum Unit

The drum unit21may be mounted on the drum container161of the main body casing2from the front of the casing2. The drum unit21may be inserted from the front of the casing2to the rear of the casing2. Further, the drum unit may be subsequently removed.

This drum unit21may include a photoconductor cartridge and four drum subunits23. Each of the drum subunits23may correspond to one of the toner colors, thereby forming an image carrier unit. More particularly, the drum subunit23includes four parts, which are a yellow drum subunit23Y, a magenta drum subunit23M, a cyan drum subunit23C, and a black drum subunit23K.

Each of the drum subunits23is arranged in parallel at intervals in the front and back direction. For instance, the drum subunits23may be arranged from the front to back in the following order: yellow drum subunit23Y, magenta drum subunit23M, cyan drum subunit23C, and black drum subunit23K.

Each of the drum subunits23includes (as described below) a left side frame70, a right side frame71, and a center frame72(seeFIG. 4).

Each of the drum subunits23, as shown inFIG. 2, may include a photosensitive drum as image carrier24, a scorotron-type charger25, and a cleaning brush68.

The image carrier24is arranged in the width direction (left and right direction). The image carrier24may include a cylindrical drum body26. The top surface of the cylindrical drum body26may be made of a positively charged photoconductive polycarbonate layer. The image carrier24may also include a drum shaft27arranged along the axis direction of the drum body26.

The ends of the drum shaft27are inserted in the right side frame71and the left side plate95of the center frame72(seeFIG. 4), respectively. Also, the ends of the drum shaft27are aligned by the side plate121(seeFIG. 7).

Rotary supporting members30(seeFIG. 9) fit snuggly onto both ends of image carrier24so that the drum body26and the drum shaft27cannot rotate relative to each other. The rotary supporting members30are supported by the outside periphery of the drum shaft27. By doing so, the drum body26is supported by the drum shaft27in a rotatable manner. During the image formation, a driving force from a motor (in main body casing2) is transmitted to the image carrier24. In response, the image carrier24rotates.

A scorotron-type charger25faces the image carrier24with a diagonal gap on the top rear of the image carrier24. The scorotron-type charger25is supported by the center frame72. This scorotron-type charger25includes a discharging wire28that faces the image carrier24. Between the discharging wire28and the image carrier24is a gap. A grid29is provided between the discharging wire28and the image carrier24.

A wire electrode80(seeFIG. 5) is connected to the discharging wire28. The grid electrode81(seeFIG. 5) is connected to the grid29.

During image formation, a high voltage is applied to the discharging wire28via the wire electrode80from the high voltage substrate in the main body casing2. The discharging wire27performs corona discharging at the same time a voltage is applied to the grid29via the grid electrode from the high voltage substrate. As a result, the surface of the image carrier24is uniformly positively charged while the electric charge supplied to the image carrier24is controlled.

A cleaning brush68contacts the image carrier24at the rear of the image carrier24. The cleaning brush68is supported by the center frame72. During the image formation, a cleaning bias is applied to the cleaning brush68from the high voltage substrate via the cleaning electrode (seeFIG. 5).

(2-2-2) Developing Cartridge

As shown inFIG. 1, the developing cartridges22are arranged so that they can be attachable/removable from the drum subunits23that correspond to each color. The developing cartridges22may include four parts, which are a yellow developing cartridge22Y that is insertably/removably mounted on the yellow drum subunit23Y, a magenta developing cartridge22M that is insertably/removably mounted on the magenta drum subunit23M, and a cyan developing cartridge22C that is insertably/removably mounted on the cyan drum subunit23C, and a black developing cartridge22K that is insertably/removably mounted on the black drum subunit23K.

As shown inFIG. 3, each of the developing cartridges22may include a developing frame31(as an example of a casing), an agitator32, and a supplying roller33(provided in the developing frame31), a developer carrier34(an example of a developing powder carrier), and a layer thickness limiting blade35.

The developing frame31may be formed in a box shape in which an opening36opens at the bottom edge (seeFIG. 11). The developing frame may be divided into a toner container37and a developing chamber38with a partition39. A connecting hole40that connects the toner container37and developing chamber38may be provided on the partition39.

Toner that corresponds to each color is contained in the toner containers37, respectively. More specifically, the yellow developing cartridge22Y may contain yellow toner, the magenta developing cartridge22M may contain magenta toner, the cyan cartridge22C may contain cyan toner, and the black developing cartridge22K may contain black toner.

A positively charged polymerization toner with a non-magnetic single component may be used as the toner that corresponds to each color. The particles of the polymerization toner may be approximately spherical in shape. The main component of the toner may be a binding resin that can be obtained by copolymerizing styrene monomers such as styrene and acrylic monomers including but not limited to acrylic acid, alkyl (C1-C4) acrylate, and alkyl (C1-C4) metaacrylate (using publicly known polymerization methods such as suspension polymerization). The toner base particle may be formed by adding one or more coloring agents (to provide the various colors of the toner), a charge control agent, and wax. An additive may be added to improve flowability of the toner.

Coloring agents (for instance, yellow, magenta, cyan and black) are blended as coloring agents. In addition, a charge control resin (which can be obtained by the copolymerization of ionic monomers having an ionic function group such as an ammonium salt), monomers (that can be copolymerized with ionic monomers such as styrene monomers), and acrylic monomers may be blended as a charge control agent. In addition, inorganic powders may be blended as an additive. These inorganic powders may include metal oxide powders, such as silica, aluminum oxide, titanium oxide, strontium titanate, cerium oxide or magnesium oxide and carbide powders and metallic salt powders.

Windows142for detecting the remaining amount of toner contained in the toner container37are provided on the toner container37. The windows are located on both sidewalls141. The windows face each other over the toner container43(seeFIG. 17).

An agitator32is provided in the toner container37. The agitator32includes a rotary shaft41. The rotary shaft41may be supported by both sidewalls141of the developing frame31so that the rotary shaft41can rotate. The agitator32may also include an agitating member42that is provided in the axis direction of the agitator rotary shaft47. The agitating member47may extend externally from the rotary shaft in the direction of the diameter of the developing frame31. During the image formation, a driving force is transmitted from a motor (not shown) to the rotary shaft41. In response, the agitating member42revolves in the toner container37.

The supplying roller33is provided in the developing chamber38below the connection hole40. The supplying roller33includes a metallic supplying roller shaft43that is supported by both sidewalls141of the developing frame31so that the supplying roller33can rotate. The supplying roller33also includes a sponge roller44that may be made of a conductive sponge. The sponger roller44may also encircle the supplying roller shaft43. During image formation, a driving force is transmitted from a motor to the supplying roller shaft43via the passive coupling gear144(seeFIG. 12). In response, the supplying roller38rotates.

The developer carrier34is arranged diagonally against the diagonal back bottom of the developing chamber38relative to the supplying roller33. This developer carrier34includes a metallic developer carrier shaft45. The metallic developer carrier shaft45is supported by both sidewalls141of the developing frame31so that the carrier shaft45can rotate. The carrier shaft45is also supported by a rubber roller46. The rubber roller46may be made of conductive rubber that covers the developer carrier shaft45.

More specifically, the rubber roller46may have a two-layer structure that includes a rubber roller layer that is made of a conductive urethane rubber, a silicon rubber or EPDM rubber containing carbon microparticles, etc., and a coating layer that is coated on the surface of the rubber roller layer. A main component of the rubber roller layer may be a resin with superior anti-abrasive performance such as urethane rubber, a urethane resin, or a polyimide resin. In addition, a feed coil155(seeFIG. 5) as a feeder of the developer carrier electrode82may be used with the developer carrier shaft45when the developing cartridge22is inserted in the drum sub-unit23.

The developer carrier34can be arranged so that the rubber roller46and sponge roller44contact each other with pressure relative to the supplying roller33. In addition, the developer carrier34can be arranged so that the developer carrier34is exposed downstream from the opening36of the developing chamber38(seeFIG. 11).

During image formation, a driving force is transmitted from a motor (not shown) to the developer carrier shaft45. In response, the developer carrier34rotates. In addition, a developing bias is applied from the high voltage substrate (not shown) via the developer carrier electrode82and feed coil155.

The layer thickness limiting blade35contacts an upper side of the developer carrier34with pressure in the developing chamber38. The layer thickness limiting blade35includes a blade48that includes a metal plate spring member and a pressing portion49with a semi-circular cross-section. The pressing portion49is provided on the unattached end of the blade48. The pressing portion49may be made of insulating or conductive silicone rubber or urethane rubber.

The anchored end of the blade48is fastened to the partition39by a fastening member47. The blade48may be elastic. Because of this elasticity of the blade48, the pressing portion49provided on the loose end of the blade48is evenly pressed against the top of rubber roller46of the developer carrier34.

(2-2-3) Developing Operation at the Processing Unit

As shown inFIG. 3, the toner contained in the toner container37moves downward to the connection hole40at least in part because of the weight of the toner. While being agitated by the agitator32, the toner is discharged through the connection hole40toward the developing chamber38.

Next, the toner is discharged from the connection hole40to the developing chamber38. From the developing chamber38, the toner is supplied to the supplying roller33. The toner supplied by the supplying roller33is conveyed to the developer carrier34by the rotation of the supplying roller33. During rotation of supplying roller33, a positive frictional charge is generated between the supplying roller33and the developer carrier34where the developing bias is applied.

The toner supplied to the developer carrier34enters between the pressing portion49of the layer limiting blade35and the rubber roller46of the developer carrier34. The supply of the toner is assisted by the rotation of the developer carrier34. The toner is transported on the surface of the rubber roller46as a thin layer with a relatively constant thickness.

As shown inFIG. 2, in the drum subunits23, the scorotron-type charger25generates a corona discharge. The scorotron-type charger25charges the surface of the image carrier24with a uniform positive charge.

The surface of the image carrier24is uniformly positively charged by the scorotron-type charger25as the image carrier24is rotated. Next, the surface of the image carrier24is exposed by the high speed scanning of the laser beam from the scanner17. The scanning imparts an electrostatic lateral image that corresponds to the image to be formed on the paper3.

When the image carrier24contacts the developer carrier34, the toner on the surface of the developer carrier34is transferred to the surface of the image carrier24in the shape of the latent electrostatic image provided by the scanning of the laser. The exposed portion where the electric potential is low is due to the exposure by the laser beam on the surface of the uniformly positively charged image carrier24. Using this process, the electrostatic latent image of the image carrier24is developed to be a visible image. The toner image by the reversal development is performed for each color on the surface of the image carrier24.

The remaining toner that remains on the image carrier24after toner transfer to the paper is collected by the developer carrier34. The paper dust from the paper3that is remains on the image carrier24is then collected by the cleaning brush68.

(2-3) Transfer Portion

Referring toFIG. 1, the transfer portion19is arranged in the main body casing2above the paper feed4and below the processing unit18, along the front and back direction. This transfer portion19includes a driving roller51, a driven roller52, a feed belt53, a transfer roller54, and a cleaning portion55.

The driving roller51and driving roller52face each other with a gap in the front and back direction. The driving roller51is arranged on the back side of the black drum subunit23K. The driven roller52is arranged on the front side of the yellow drum subunit23Y.

The feed belt53may be an endless belt. The feed belt53is made of a resin film such as a conductive polycarbonate and polyimide. Conductive particles (such as carbon) may be on or in the resin film. The feed belt53is conveyed between the driving roller51and the driven roller52.

During image formation, a driving force is transmitted from a motor. The driving force is provided to the driving roller51. In response, the driving roller51rotates. Then, the feed belt53is then conveyed between the driving roller51and the driven roller52at the transferring position. The transferring position is where the feed belt53contacts the image carrier24of each of the drum subunits23. The feed belt53rotates in the opposite direction from the image carrier24at the same time the driven roller52is driven.

The transfer rollers54are arranged along the path of the feed belt so that the transfer rollers contact an opposite side of the feed belt53from the image carriers24. Each of the transfer rollers54has a metal roller shaft with a rubber roller, which is made with conductive rubber. In addition, each of the transfer rollers54is arranged at the transferring position and contacts the feed belt53so that each transfer roller54is driven and rotates in the same direction as the revolving direction of the feed belt53. During image formation, a transfer bias is applied from the high voltage substrate.

The cleaning portion55is provided below the feed belt53. The cleaning portion55includes a primary cleaning roller56, a secondary cleaning roller57, a scraping blade58, and a toner storage59.

The primary cleaning roller56contacts the bottom of the feed belt53. The bottom of the feed belt53is on the opposite side from the top of the feed belt53(where the image carrier24and the transfer roller54contact the feed belt53). During image formation, the primary cleaning bias is applied to the primary cleaning roller56from the high voltage substrate.

The secondary cleaning roller57contacts the primary cleaning roller56on the bottom side of the primary cleaning roller56. At this location, the secondary cleaning roller57rotates in the same direction as the rotation direction of the primary cleaning roller56. Also, during image formation, a secondary cleaning bias is applied to the secondary cleaning roller57from the high voltage substrate.

The scraping blade58contacts the bottom of the secondary cleaning roller57.

The toner storage59is arranged below the primary cleaning roller56and the secondary cleaning roller57so that toner storage59accumulates the toner dropped from the secondary cleaning roller57.

The paper3fed by the paper feed4is carried by the feed belt from the front side to the back side so that paper3passes through the transfer positions at each of the drum subunits23in sequence. The toner images in each color on the image carrier24of each of the drum subunits23are transferred in sequence to paper3. Accordingly, a color image is formed on the paper3.

In other words, for example, after a yellow toner image on the surface of the image carrier24of the yellow drum subunit23Y is transferred to the paper3, the magenta toner image (on the surface of the image carrier24of the magenta drum subunit23M) and the cyan toner image (on the surface of the image carrier24of the cyan drum subunit23C) are transferred in layers. Next, a black toner image on the surface of the image carrier24of the black drum subunit23K is transferred to the paper3. The result is a color image formed on paper3.

During the transfer operation, the toner attached on the surface of the feed belt53is transferred at the cleaning portion55. First, the toner is transferred from the surface of the feed belt53to the primary cleaning roller56by the primary cleaning bias. Next, the toner is transferred to the secondary cleaning roller57by the secondary cleaning bias. The toner transferred to the secondary cleaning roller57is next scraped by the scraping blade58. The toner then falls from the secondary cleaning roller57and accumulates in the toner storage59.

The fixing portion20is arranged on the rear side of the black drum subunit23K so that the fixing portion20faces the transfer position where the image carrier24and the feed belt53contact each other in the front and back direction. This fixing portion20includes a heating roller61and pressurizing roller62.

The heating roller61includes a metal tube (where a releasing layer is formed on the metal tube's surface) and a halogen lamp arranged in the axis direction of the heating roller61. The surface of the heating roller61is heated to the fixing temperature by the halogen lamp.

The pressurizing roller62is arranged below the heating roller61and facing the heating roller61. The pressurizing roller62presses the bottom of the heating roller61. The paper3having the color image is conveyed to the fixing portion20. As paper3passes between the heating roller61and the pressurizing roller62, the thermal fixing of the toner on the paper3is performed.

(3) Paper Discharge Portion

At the paper discharge portion, the upstream side edge of the paper discharging side feed pathway63for the paper3is adjacent to the bottom of the fixing portion20. The downstream side edge of the paper discharging side feed pathway63is adjacent to the top of the paper discharge tray64. The paper discharging side feed pathway63is formed in an approximately U-shape from the side. Here, the paper3is fed towards the back, reversed, and then discharged to the front.

At the middle of the paper discharge side feed pathway63, a feed roller65and pinch roller66face each other. In addition, a pair of paper discharge rollers67is provided on the downstream edge of the paper discharge side feed pathway63.

Further, a paper discharge tray64is provided on the paper discharge portion6. The paper discharge tray64is formed such that the top wall of the main body casing2gradually sags from the front to the back. Accordingly, the discharged paper3can be loaded in layers.

The paper3from the fixing portion20is carried along the paper discharging side feed pathway63by the feed roller65and the pinch roller66. The paper3is then discharged into the paper discharge tray64by the paper discharge roller67.

2. DRUM UNIT

FIG. 4is an exploded perspective view of the drum unit26.FIG. 5is a right lateral perspective view that shows four drum subunits and a rear beam being arranged in parallel.FIG. 6is a left lateral perspective view that shows a front beam, four drum subunits, and a rear beam being arranged in parallel and a pair of side plates.

FIG. 7is a right lateral perspective view of the drum unit21(the developing cartridge is being installed).FIG. 8is a left lateral perspective view of the drum unit21(the developing cartridge is being installed).FIG. 9is a left lateral perspective view that shows the installation of one of the developing cartridge to the drum unit21.FIG. 10is a left lateral view that is viewed from the upper position compared toFIG. 9, whereFIG. 10shows the installation of one of the developing cartridge to the drum unit21.

FIG. 11is a back view of the developing cartridge.FIG. 12is a left lateral perspective view of the developing cartridge showing the back lateral surface of the developing cartridge.FIG. 13is a right lateral perspective view of the developing cartridge showing the front lateral surface of the developing cartridge.FIG. 14is a plane view of the drum unit21in which one of the developing cartridges is removed.FIG. 15is a right lateral view of the drum unit21shown inFIG. 14, in which the side plate is removed and the right guiding groove of the two front side drum subunits23is exposed for explanation.FIG. 16is a left lateral view of the drum unit21shown inFIG. 14, in which the side plate is removed.FIG. 17is a cross-sectional view that is cut across the line A-A inFIG. 14.

FIG. 22is a right lateral perspective view that shows the front beam, four drum subunits23, and the rear beam being arranged in parallel.FIG. 23is a left lateral perspective view that shows the condition in which the front beam, four drum subunits23, and the rear beam are arranged in parallel and a pair of side plates is assembled.

Next, the drum unit is described in detail by referring to theFIGS. 4 to 17andFIGS. 22 and 23.

The drum unit21, as shown inFIG. 6, may include four drum subunits23(corresponding to each color), a front beam96, and rear beam111that are arranged on both sides along the front and back direction of the four drum subunits23. The drum subunits are arranged in parallel along the front and back direction.FIG. 6also shows a pair of side plates121that sandwich the front beam96, four drum subunits23, and rear beam111from the sides in the width direction.

The drum unit21(including four drum subunits23, front beam96, rear beam111and a pair of side plates121) can be inserted/removed by sliding from the drum housing space162in the main body casing2(seeFIG. 1).

As shown inFIG. 4, the drum subunit23may include a left side frame70and right side frame71that face each other. A center frame is between the left side frame70and right side frame71.

(1-1) Side Frame

The left side frame70and right side frame71are made of a resin material. The left side frame70has an approximate triangle shape. When viewed from the side, the left side frame70becomes narrower from the top to bottom. The right side frame71is in an approximate parallelogram shape. When viewed from the side, the right side frame71inclines from the front top to the rear bottom.

A right guiding groove73is formed on the internal wall of the right side frame71. The right guiding groove73functions as the powered portion guiding groove.

The right guiding groove73is formed on the internal wall of the right side frame71. The right guiding groove73extends from the rear side upper edge of the right side frame71to near the front side bottom edge of the right side frame71. The right guiding groove73extends approximately along the top-bottom direction. The right guiding groove73has a concave shape with a squared U-shaped cross-section when viewed from the internal wall of the right side frame71in the width direction. The top edge of the right guiding groove73is open. The top of the right guiding groove73has a wide width as well. Moving downward, the right guiding groove73has a constant groove width A (see the double ended arrow inFIG. 4). The right guiding groove73bends in front of the bottom edge towards the diagonal bottom rear. The lowest portion154of the right guiding groove73corresponds to the position of the developer carrier shaft45where the developer carrier34contacts the image carrier24when the developing cartridge22is installed in the drum subunit23. The groove width B (see the dotted arrow inFIG. 4) at the deepest portion154is smaller than the above-described groove width A. A collar member50(which is an alignment portion for the developing cartridge) and a cylindrical portion184(seeFIG. 11) of the powered member182(which is the powered portion) slide in right guiding groove73.

A notch201is formed on the groove wall on the front side at the bent position of the right guiding groove73described above. The right guiding groove73extends through the right side frame71via this notch201.

A boss75is formed on the front upper side relative to the right guiding groove73on the right side frame71. The boss75is also formed at the position that faces the boss75of the left side frame70. Bosses75are formed in a cylinder shape that externally projects in the width direction from the external wall of the right side frame71and left side frame70. The bosses75are arranged so that, while the developing cartridge22is mounted on the drum subunit23, the windows142of the developing cartridge22align with bosses75(seeFIG. 13).

In addition, as shown inFIG. 5, a supporting shaft156is formed on the bottom front edge of the right lateral surface of the right side frame71. The supporting shaft156is formed in a cylinder shape. The supporting shaft156projects from the right lateral side of the right side frame71to the outside in the width direction (right side).

Furthermore, as shown inFIG. 4, a drum support76that supports the image carrier24is formed on the bottom edge of the right side frame71. The drum support76is concave with a cylindrical shape from the internal wall surface of the right side frame71towards the outside in the width direction. The drum support76includes a receptacle77that receives the shaft insertion tube90of the center frame72described below.

At the center of the receptacle77, a shaft insertion hole78penetrates the right side frame71in the thickness direction.

In addition, two screw insertion holes79are formed on the rear edge of the right side frame71. The two screw insertion holds79penetrate in the thickness direction. The two screw insertion holes79permit screws92to connect right side frame71to the center frame72. One of the screw insertion holes79is formed at the bottom edge of the rear edge of the right side frame71. The other screw insertion hole79is formed in the middle of the top-to-bottom direction of the rear edge of the right side frame71.

Convex strips84extend along the front and back direction. The convex strips84are formed on the left side frame70and right side frame71at the top of the bosses75. These convex strips84project outwardly in the width direction from the external wall of the left side frame70and the right side frame71. The convex strips84are formed in a long narrow strip shape along the front and back direction.

In addition, the left side frame70is, as described above, an approximate triangle shape when viewed from the side. A front side perpendicular wall60that extends in the approximate top and bottom direction is formed on the left side frame70. A front concave portion69is formed on the bottom edge of the front perpendicular wall60. The front concave portion69is formed in an approximate arc shape when viewed from the side in which the front perpendicular wall60sags to the front side. The left side frame70then continues from the front perpendicular wall60. In addition, the top edge of the front perpendicular wall60and the rear edge of the top surface of the left side frame70are connected with an inclined surface that extends towards the diagonal front top.

A screwing portion85is provided at the bottom edge of the left side frame70. The screwing portion85allows a screw136to attach the left side frame70to the side plate121. This screwing portion85is formed in a tube shape that externally projects from the outside wall of the left side frame70in the width direction.

Moreover, an alignment projection200frontally projects from the front side surface of the left side frame70. The alignment projection200is formed below the front edge of the convex strip84at the front lateral surface of the left side frame70.

A sidewall opening213is formed between the boss75and front perpendicular wall60of the left side frame70. The sidewall opening213is formed as a narrow rectangular shape, when viewed from the side, and extends along the top and bottom direction as shown inFIG. 23(not shown inFIG. 4). A lever supporting shaft214having a cylinder shape is supported between the front edge and rear edge of the sidewall opening213, on the top edge of the sidewall opening213.

A lever206is supported by the lever supporting shaft214in a movable manner.

The lever206is formed in an approximate reverse L-shape, when viewed as a vertical cross-section. The level206has two edges over the lever moving shaft207that is inserted in the lever supporting shaft214. One end of level206projects to the right side from the sidewall opening213. The other end of level206projects to the left from the sidewall opening213.

As shown inFIG. 5, a wire electrode80, a grid electrode81, a developer carrier electrode82, and a cleaning electrode83are supported in right side frame71. These elements penetrate the right side frame71in the thickness direction and externally project from the outside wall of the right side frame71in the width direction.

The wire electrode80is arranged at the approximate center in the front and back and top and bottom directions on the right side frame71, above the shaft insertion hole78.

The grid electrode81is arranged at the middle in the top and bottom direction on the rear edge of the right side frame71. The grid electrode81is arranged on a diagonal to the upper rear of the shaft insertion hole78.

The developer carrier electrode82is arranged in the middle in the top and bottom direction on the front edge of the right side frame71. The developer carrier electrode82is also located along a diagonal to the upper front of the shaft insertion hole78. In addition, a feed coil155is connected to the developer carrier electrode82.

As shown inFIG. 22, the feed coil155may include a winding portion157. The winding portion157includes a conductive wire material such as metal wire. The feed coil155is wound one time or greater with winding portion157. The winding portion157may also include one arm158and another arm159that project away from each other in the tangential line direction from the winding portion157.

The feed coil155is arranged so that winding portion157is inserted to the supporting shaft156of the right side frame71. Also, one arm158is arranged along the front edge of the right side frame71towards the diagonal upper front. The unattached edge of arm158is connected to the developer carrier electrode82. The other arm159extends in front of one arm158in the diagonal upper front direction. The other arm159is latched by a hook160when viewed as a vertical cross-section (provided above the supporting shaft156at the approximate center in the top and bottom direction). The other arm159bends towards the rear from the position latched by the hook160. The other arm159forms an approximate arch shape, when viewed from the side, from the latched portion by the hook160to the unattached end. The above-described convex portion176forms an approximate arch shape and projects from the notch201of the right guiding groove73into the right guiding groove73, when viewed from the side and when the feed coil155is assembled with the right side frame71.

As shown inFIG. 5, the cleaning electrode83is arranged at the middle in the top and bottom direction of the rear edge of the right side frame, above the grid electrode81, and diagonal to the upper rear of the shaft insertion hole78.

A peripheral fitting wall94externally projects in a semicircle shape in the width direction by surrounding the wire electrode80on the external wall of the right side frame71.

(1-2) Center Frame

As shown inFIG. 4, the center frame72may be formed from resin material independently from the left side frame70and right side frame72. Center frame72includes a center plate86(that extends in the width direction), a right side plate87, and a left side plate95(that are provided on both edges of the center plate86in the width direction in an integrated manner). The right side frame71and the combination of the left side plate95and the left side frame70function as a pair of guiding walls.

The center plate86has a narrow plate shape when viewed from the top. The center plate86includes a charger retainer88(which keeps the scorotron-type charger25along the width direction), which is provided at the middle of the center plate86in the top-bottom direction.

A discharge wire28is located on the charger retainer88along the width direction. A grid29is held below the wire28(seeFIG. 2). In addition, a wire cleaner89that holds the discharge wire28is held in the width direction on the charger retainer88in a slidable manner.

A brush holder93holds cleaning brush68below the charger retainer88on the center plate86.

The cleaning brush68extends along the width direction in the brush holder93(seeFIG. 2).

In addition, an alignment roller218is provided on both edges in the width direction at the top edge of the center plate86. The alignment roller218is supported by the roller supporting shaft219. The roller supporting shaft219is provided along the width direction of both edges in the width direction of the top edge of the center plate so that the roller supporting shaft219can freely rotate (seeFIG. 10).

The right side plate87and the left side plate95extend forward by bending from the center plate86at both edges in the width direction of the center plate86. The right side plate87and left side plate95are formed in an approximate triangle shape with the narrow side on the top when viewed from the side. A shaft insertion tube90(in which drum shaft27is inserted) is provided at the front edge.

A screwing portion91is provided at the top and bottom edge of the right side plate87. The screwing portion91allows the screw92to be screwed in order to assemble the right side frame72to the center frame72. The screwing portion91is formed in a tube shape that externally projects from the outside wall of the right side plate87in the width direction.

The left side plate95is larger than the right side plate87. The left side plate95has an approximate right angled triangle-shape. The left side plate95may include a base wall137(extending in the front and rear direction), a rear side perpendicular wall138(extending upwards in an approximately vertical direction from the front edge of the base wall137), and an inclined wall139(connecting the rear edge of the base wall137and the top edge of the rear side perpendicular wall138). The top edge of the rear side perpendicular wall138and the top edge of the inclined wall139may be connected by an inclined surface that extends in the diagonally upper rear direction.

A rear side concave portion152is formed at the approximate center of the rear side perpendicular wall138. So as to be continuous with the rear-side perpendicular wall138, the concave portion152is formed in an approximate arc shape, when viewed from the side, so that the rear side perpendicular wall138is concave to the rear.

The groove-shaped deepest portion153is continuously concave from the bottom edge of the rear side concave portion152in the diagonally bottom rear direction. The groove-shaped deepest portion153is formed on the rear side perpendicular wall138. The groove width of the deepest portion153is the same as the groove width B described above. In addition, the deepest portion153corresponds with the position of the developer carrier shaft45(where the developer carrier34contacts the image carrier24when the developing cartridge22is being installed in the drum subunit23).

In a first example, the combination of the concave portions152and69may be used to create a seated position to which the developer cartridge22may be guided. In other examples, only one or neither of the concave portions152and69may be used to create the same position at which the developer cartridge22may be seated.

In a first aspect, the left and right side frames70and71may be part of a unit that contains the image carrier24. In another aspect, the left and right side frames70and71may be separate from the image carrier24. Here, the developer cartridge22may be first positioned in the left and right side frames70and71. Next, the combination of the left and right side frames70and71and the developer cartridge22may be moved to a location where the developer carrier22contacts the image carrier24. For instance, the left and right side frames70and71may be part of drum subunit23, where seating the developer cartridge22brings the developer carrier34into contact with the image carrier24. Alternatively, a drum subunit23may not have drums associated with the drum subunit23, but rather the drums may be located within a printer body separate from the drum subunit with left and right side frames70and71. Here, the developer cartridge22may be positioned with respect to the side frames70and71. After being positioned, the subunit and developer cartridges22may then be positioned so that the developer cartridges22contact the image carriers24.

A concave alignment portion202may be provided at the position approximately one third from the top edge of the inclined wall139, in the top and bottom direction on the inclined wall139.

Although not shown in the drawing, a drum support76that supports the image carrier24is formed on the left side plate95. At the center of drum support76, a shaft insertion hole78penetrates in the thickness direction of the left side plate95.

A screwing portion85that allows the screw136(seeFIG. 23) to be screwed in order to assemble each of the side plates121to the drum subunit23is provided above the shaft insertion tube90of the left side plate95. This screwing portion85is formed in a tube shape that externally projects from the outside wall of the left side plate95in the width direction. In addition, the convex strip84that extends along the front and rear direction is formed on top of the left side plate95.

(1-3) Assembly of the Drum Subunit

As shown inFIG. 4, the right side frame71is arranged on the right side in the width direction of the center frame72. Then the shaft insertion tube90is fit into the receptacle77so that the shaft insertion tube90is located on top of the shaft insertion hole78at the drum support76of the right side frame71in the width direction. At the same time, the screwing portion91of the center frame72is arranged so that the screwing portion91is located on top of the screw insertion hole79of the right side frame71in the width direction. Then the screws92are inserted to each of the screw insertion holes79. Next, the screws92are attached by screwing into each of the screwing portions91. By doing so, the right side frame71is assembled on the right side of the center frame72.

In addition, as shown inFIG. 5, when the right side frame71is assembled on the right side in the width direction of the center frame72, the wire electrode80and the grid electrode81(provided on the right side frame71on the right) are connected to the discharge wire28and the grid29of the center frame72, respectively. The cleaning electrode83is connected to the cleaning brush68.

As shown inFIG. 4, while the right side frame71is assembled on the right side in the width direction of the center frame72, the left side frame70is not assembled to the center frame72and the right side frame71. Instead, the left side frame70is assembled to the side plate121(described below). When the center frame72(to which the right side frame71is assembled) is assembled with the side plate121(to which the left side frame70is assembled), the drum subunit23is completed. This assembly is described below.

As shown inFIG. 6, when the drum subunit23is completed, the rear side perpendicular wall138of the left side plate95and the front side perpendicular wall60of the left side frame70face each other in the front and rear direction of the center frame72. At this time, a certain facing distance C (see solid arrow inFIG. 6) is configured between the rear side perpendicular wall138and the front side perpendicular wall60. Also, the gap between the rear side perpendicular wall138and the front side perpendicular wall60forms the left guiding groove189as the driving input portion guiding groove. The right guiding groove73, the left side guiding groove189, the right side frame71(where the right guiding groove73is formed), the left side frame70(where the left guiding groove189is formed), and the center frame72function as the guiding portion.

In addition, the facing distance C (hereinafter referred to as groove width C of the left guiding groove189) is set to be larger than the groove width A (ofFIG. 4) of the right side groove73. Next, an internal coupling insertion portion74in a circular shape, when viewed from the side, is formed by locating the rear side concave portion152of the left side plate95and the front side concave portion69of the left side frame70together by facing with each other so that the approximate arc portions, when viewed from the side, are put together.

As shown inFIG. 9, the image carrier24is held in the drum subunit23. In other words, the drum main body26, where the rotary supporting member30is inserted so the drum main body26does not relatively rotate, is arranged between the right side plate87and the left side plate95so that the drum main body26, the right side plate87, and the left side plate95are in parallel with the scorotron-type charger25leaving a gap. Next, as shown inFIG. 4, the drum shaft27is inserted into each of the shaft insertion tubes90of the center frame72and each of the shaft insertion holes78of the right side frame71. Next, each of the shaft insertion tubes90is fastened so that the shaft insertion tubes90do not relatively rotate. The drum shaft27supports the rotary support30(which supports the drum body26in a relatively non-rotatable manner). Also, the image carrier24is held by the drum subunit23.

(2) Front Beam

As shown inFIG. 5, the front beam96is arranged on the front of the four drum subunits23that are arranged in parallel along the front and back direction. The front beam96is installed between a pair of side plates121as shown inFIG. 6.

The front beam96includes a pair of frontal sidewalls97that face each other in the width direction, and a frontal front wall98and the frontal rear wall99that are installed between the pair of frontal sidewalls97. The front beam96may be formed in an integrated manner as being made of a resin material.

Each of the frontal sidewalls97includes a front sidewall base100in an approximate parallelogram plate shape, when viewed from the side, and a frontal sidewall leg101that extends downward from the bottom edge of the frontal sidewall base100. A front screwing portion103(where the screw136is screwed and described below) for assembling the side plate121is provided on the external wall of the frontal sidewall base100.

In front of the front screwing portion103of each of the frontal sidewalls97, a bearing hole203is formed so that the front beam96can penetrate in the width direction. An alignment shaft204is inserted into the bearing hole203so that both of its edges project externally in the width direction from each of the frontal sidewalls97.

The rear edge surface that continues from the frontal sidewall base100to the frontal sidewall leg101is formed as the front side inclined surface102that inclines from the front top to the rear bottom on the frontal sidewall97. A concave alignment portion215is provided on the top edge at the left edge of the front side inclined surface102(seeFIG. 6).

The frontal front wall98has an approximately narrow rectangular plate shape, when viewed from the front. The frontal front wall98extends in the width direction. The frontal front wall98is arranged along the top and bottom direction between a pair of frontal sidewalls97.

A near-side graspable portion104is provided at the center in the width direction of the frontal front wall98. This near-side graspable portion104includes a pair of graspable side plates105(arranged to face each other with a gap in the width direction) and a graspable center plate106(installed between the graspable side plates105).

The base of each of the graspable side plates405(the end that is not connected to the graspable center plate106) of the near-side graspable portion104moves between the stowed position (shown as a broken line) in a standing position and the operation position (shown as a solid line). The base of each of the graspable side plates405is in an inclined position along the approximately horizontal direction while being rotatably supported by the alignment shaft204in a rotatable manner.

The near-side graspable portion104is arranged so that the center in the width direction matches the center of the front beam96in the width direction.

As shown inFIG. 10, the frontal rear wall99has a narrow rectangular plate shape, when viewed from the back, which extends in the width direction. The frontal rear wall99is arranged on the back of the frontal front wall98. This frontal rear wall99is installed between each of the frontal sidewalls97so that frontal rear wall99inclines from the front top to the rear bottom along the front-side inclined surface102of each of the frontal sidewalls97.

The above-described alignment rollers218and alignment projection219are provided at an approximate center position in the top and bottom direction on both edges of the frontal rear wall99. The alignment projection219is arranged so that the alignment projection219is mostly embedded in the frontal rear wall99. Also, each of alignment rollers218is arranged so that a portion of each of alignment rollers218's circumference is projected from the frontal rear wall99when viewed from the side.

The rear beam111is arranged on the back side of the four drum subunits23. The rear beam is also located between a pair of the side plates121.

As shown inFIG. 5, the rear beam111may include a pair of rear sidewalls112that are arranged so that the pair of rear sidewalls112face each other in the width direction. Also, the rear beam111may include a rear installed wall113arranged between the pair of rear sidewalls112. The rear beam111may be formed from a resin material and be integrated with the pair of rear sidewalls112and the rear installed wall113.

The rear sidewall112may have an approximately triangular plate shape with the narrow side at the bottom, when viewed from the side. The rear sidewall112may also have two rear screwing portions114where the screws136for assembling the side plate121are provided at the top edge and the approximate center. Below the rear screwing portion114(provided at the approximate center of the rear sidewall112), a rear sidewall leg107is formed. A rear sidewall notch108(that is concave towards the front) is formed between the rear screwing portion114, which is formed at the approximate center, and the rear sidewall leg107. In addition, the front edge of the rear sidewall112is formed as the rear side inclined surface115that inclines from the top front to the rear bottom.

The rear installation wall113has a narrow rectangular plate shape, when viewed from the front, which extends along the width direction. The rear installation wall113is arranged along the top and bottom direction between the pair of rear sidewalls112.

A far-side graspable portion116is provided at the center in the width direction of the rear installation wall113. As shown inFIG. 10, the far-side graspable portion116may include a graspable concave portion117in which the top edge of the rear installation wall113sags in a concave shape towards the bottom when viewed from the back. The far-side graspable portion116may also include a rear handle118having an approximate square U shape when viewed from the back, which is connected to the top edge of the rear installation wall113. Accordingly, the far-side graspable portion116may then be located over the graspable concave portion117in the width direction.

This far-side graspable portion116is arranged so that the center in the width direction matches the center in the width direction of the rear beam111.

(4) Side Plates

As shown inFIG. 6, a pair of side plates121is provided so that the side places121can sandwich the front beam96, four drum subunits23, and rear beam111from both sides in the width direction.

Each of the side plates121is made of a material with a lower linear expansion coefficient than the linear expansion coefficient of the resin material for forming the drum subunits23. For example, the side plates121may be made of a metal or fiber reinforced resin, and preferably, is made of metal.

As shown inFIG. 23, each of the side plates121has an approximately narrow rectangular shape that extends in the front and back direction when viewed from the side. Each of the side plates121is formed so that the front edge faces the front beam96, and the rear edge faces the rear beam111, relative to the front beam96, four drum subunits23and rear beam111. The front beam96, four drum subunits23, and rear beam111may be arranged in parallel along the front and back direction, during the assembly of the drum unit21. In addition, the top edge faces the convex strip84of the left side plate95, the left side frame70and the right side frame71of the center frame72of the drum subunit23. The bottom edge faces the bottom edge of the left side plate95, left side frame70and right side frame71of the center frame72of the drum subunit23.

The top edge of each of the side plates121is externally bent in the width direction so that the top edge's cross-section is an L shape. A flange122is formed, which is externally bent in the width direction and externally extends in the width direction in the front and back direction. On the rear edge of each of the side plates, two rollers177are provided in a rotatable manner. These two rollers177are arranged in the front and back direction at a distance by sandwiching a spacer178. The front roller177is arranged below the flange122with a gap in the top and bottom direction relative to the flange122. The rear roller177is arranged with a gap relative to the rear edge of the flange122.

Furthermore, a notch179is formed at the bottom edge of the rear edge of each of the side plates121. This notch179is formed in a U-shape when viewed from the side, such that the notch179continues to the rear edge of each of the side plates122and sags forward.

Four light transmission holes123that accept the bosses75of each of the drum subunits23are formed on the top edge of each side plate121, under a condition in which each side plate121is assembled to the drum subunit23.

Each of the light transmission holes123are formed on the top edge of each side plate121at intervals along the front and rear direction. These light transmission holes123are formed as round holes that penetrate in the thickness direction at a position where each window142(seeFIG. 12) of the developing cartridge faces each boss75of each drum subunit23in the width direction (seeFIG. 4) under the condition in which each of the developing cartridges22are installed in each of the drum subunits23.

A shaft hole124, where an edge in the axis direction of the drum shaft27of each drum subunit23is inserted, is formed at the bottom edge of each of the side panels121.

A pair of latching holes (not shown) is formed on the rear top and front top diagonal to each of the shaft holes124of each side plate121. A wire spring127is latched onto these latching holes. More specifically, the wire spring127is made of a V-shaped wire that sags downwards, when viewed from the side. Also, both edges of the top side are bent externally in the width direction, and are latched to the latching holes. The front part of the wire spring127is exposed from the shaft hole124so that front part of the wire spring127inclines from the rear bottom to the front top, when viewed from the side, so that the 3 o'clock position and 6 o'clock position of the shaft hole124are connected.

Furthermore, a front side screw insertion hole128for inserting a screw136is formed on the front edge of each side plate121by facing the front screwing portion103of the front sidewall base100, under the condition in which each of the side plates is assembled to the front beam96. In addition, a shaft exposing hole216is formed at the front top, diagonally to the front side screw insertion hole128of each side plate121.

Moreover, two each of the rear side screw insertion holes129for inserting screws136are formed on the rear edge of each of the side plates121so that they face the rear screwing portion114of the rear sidewall112under the condition that each side plate121is assembled with the rear beam111. Of these rear side screw insertion holes129, a group of the rear side screw insertion holes129are formed approximately at the center in the front and rear direction of the spacer178.

In addition, on the left side plate121, an outward coupling insertion hole130that faces the passive coupling gear144of each of the developing cartridges22in the width direction is formed such that in which each of the side plates121is assembled to the drum subunit23and the developing cartridge22is mounted on the drum subunit23.

Four outward coupling insertion holes130are formed at the center in the top and bottom direction of the side plate121along the front and back direction at intervals. These outward coupling insertion holes130are formed as round holes that penetrate in the thickness direction. These insertion holes130are formed at the position where they face the coupling inward insertion holes74(formed on the left lateral surface of the drum subunit27) in the width direction in which the side plate121is assembled to the drum subunit23and the developing cartridge22is mounted on the drum subunit23.

Four lever transmission holes208that receive the other end of the lever206of each of the drum subunits23(projected to the left from the sidewall opening213) are formed on the left side plate121, on the back of each light transmission hole123under the condition in which the left side plate121is assembled to the drum subunit23.

Four lever transmission holes208are formed at the top edge of the left side plate121along the front and rear direction at intervals. These lever transmission holes208are formed with a convex shape when viewed from the side. The lever transmission holes208face each other in the thickness direction at the position where the detection gear205of the developing cartridge22and the sidewall opening213of the drum subunit23face each other when the developing cartridge22is mounted on each of drum subunits23.

Middle screw insertion holes132to insert screws136are formed on each of the side plates121and face the screwing portion85of the drum subunit23when each of the side plates121is assembled to the drum subunit23.

One each of the middle screw insertion holes132is arranged on the front and back positions of each coupling outward insertion hole130and8. Each is formed in the side plates121.

As shown inFIG. 7, on the right side plate121, a center opening133to externally expose the wire electrode80and grid electrode81(provided on each of the right side frames71in the width direction relative to the right side plate121) is formed under the condition in which each of the side plates121are assembled to the drum subunit23.

Four center openings133are formed at intervals along the front and back direction. These center openings133are formed as large openings (which allow the peripheral fitting wall94that includes wire electrode80(seeFIG. 5) to be fitted in and allow the grid electrode81to be inserted).

On the right side plate121, front openings134are formed in front of each of the center openings133in order to externally expose the developer carrier electrode82in the width direction relative to the right side plate121, when each of the side plates121is assembled to the drum subunit23. Four front openings134are formed facing the developer carrier electrode82in the width direction in correspondence to each of the center openings133when each of the side plates121is assembled to the drum subunit23.

On the right side plate121, rear openings135are formed behind each of the center openings133in order to externally expose the cleaning electrode83in the width direction relative to the right side plate121, when each of the side plates121is assembled to the drum subunit23. Four rear openings135are formed facing the cleaning electrode83in the width direction in correspondence to each of the center openings133when each of the side plates121are assembled to the drum subunit23.

(5) Assembly of the Drum Unit

First, the four drum subunits23are arranged to be adjacent with each other in the front and back direction. As shown inFIG. 6, to arrange the four drum subunits23to be adjacent with each other in the front and back direction, the alignment projection200of the left side frame of the drum subunit23in back is fit into the alignment concave portion202on the left side plate95of the center frame72of the drum subunit23in front. Also, the front edge surface of the right side frame71of the drum subunit23in back is allowed to contact the rear edge surface of the right side frame71of the drum subunit23in front. By doing so, each of the drum subunits23is arranged to be adjacent with each other in the front and back direction while each is inclined from the front top to the rear bottom.

Next, the front beam96is arranged to be adjacent to the drum subunit23at the far front. Also, the rear beam111is arranged to be adjacent to the drum subunit23at the far back. To arrange the front beam96to be adjacent to the drum subunit23at the far front, the front edge surfaces of the left side frame70and the right side frame71of the drum subunit23at the far front are brought into contact with the front inclined surface102of the front beam96. At this time, the alignment projection200of the left side frame70of the drum subunit23at the far front fits into the alignment concave portion21that is formed on the front inclined surface102. In addition, in order to arrange the rear beam111to be adjacent to the drum subunit23at the far back, the rear edge surfaces of the left side plate95and right side frame71of the drum subunit23at the far back are brought into contact with the rear inclined surface115of the rear view beam111.

And as shown inFIG. 23, each of the side plates121is arranged on both sides in the width direction of the front beam96, the four drum subunits23and rear beam111(which are arranged along the front and rear direction). Next, each of the side plates121is assembled to the front beam96, the four drum subunits, and the rear beam using screws136.

To assemble the left side plate121on the left side in the width direction of the front beam96, the four drum subunits23and rear beam111, the front screw insertion hole128of the left side plate121is arranged to face the left side front screwing portion103of the front beam in the width direction. Next, the rear side screw insertion hole129of the left side plate121is placed so that the screw insertion hold129faces the left side rear screwing portion114of rear beam111. Finally, the middle screw insertion hole132of the left side plate121is arranged so that the middle screw insertion hole132faces the screwing portion85of each of the drum subunits23in the width direction.

Next, the internal wall of the left side plate121is brought into contact with the convex strip84of the left side frame71and the convex strip84of the center frame72of each drum subunit23. The left edge in the axis direction of the drum shaft27is inserted into each of the shaft holes124of the left side plate121. At the same time, the boss75of the right side frame71on the left of each drum subunit23is fit into each of the light transmission holes123of the left side plate121so that the boss75is externally exposed in the width direction. Fitting the boss75of the right side frame71on the left of each drum subunit23limits the rotation centered about the drum shaft27relative to the left side plate121of each of the drum subunits23.

The screws136are inserted into the front screw insertion holes128. The screws136are then screwed into the front screwing portion103. Next, the screws are inserted into the rear screw insertion holes129and screwed into the rear screwing portion114. Finally, the screws136are inserted into each of the middle screw insertion holes132and screwed into each of screwing portions85. As shown inFIGS. 8 and 9, by doing so, the left side plate121is assembled on the left side of the front beam96, the four drum subunits23, and rear beam111.

As shown inFIG. 7, to assemble the left side plate121on the right side in the width direction of the front beam96, the four drum subunits23, and rear beam111, the front screw insertion hole128of the right side plate121is arranged to face the right side front screwing portion103(seeFIG. 5) of the front beam in the width direction. Next, the rear side screw insertion hole129of the right side plate121is placed so that the rear side screw insertion hole129faces the right side rear screwing portion114(seeFIG. 5) of rear beam111.

Next, the internal wall of the right side plate121is brought into contact with the convex strip84of the right side frame71and the convex strip84of the center frame72of each drum subunit23. The right edge in the axis direction of the drum shaft27is inserted into each of the shaft holes124of the right side plate121. At the same time, the boss75of the right side frame71on the right of each drum subunit23is fit into each of the light transmission holes123of the right side plate121so that the boss75is externally exposed in the width direction. In addition, the peripheral fitting wall94of each drum subunit23is fitted to the center opening133of the right side plate121. Fitting the boss75of the right side frame71on the right of each drum subunit23limits the rotation centered about the drum shaft27relative to the right side plate121of each of the drum subunits23.

Then, the screws136are inserted into the front screw insertion holes128, and screwed into the front screwing portion103. The screws136are then inserted into the rear screw insertion holes129and screwed into the rear screwing portion114. By doing so, the right side plate121is assembled on the right side of the front beam96, the four drum subunits23and rear beam111.

In the drum unit21assembled as above, both ends in the axis direction of the drum shaft27are supported between the left side plate95and right side frame71of the center frame72in each of the drum subunits23. As shown inFIGS. 7 and 8, the ends of drum shaft27are inserted into the shaft hole124of each of the side panels121.

The end in the axis direction of the drum shaft27is pressed in the direction opposite to the exposed portion, at the shaft hole124of the wire spring127, relative to the hole center of the shaft hole124. In other words, the drum shaft27is pressed diagonally in the upper rear direction, by the above-described wire spring127. By doing so, both ends in the axis direction of the drum shaft27are pressed by the wire spring127and come in contact with the peripheral border of the shaft hole124. Thus, both ends in the axis direction of the drum shaft27are aligned between the pair of side plates121.

In addition, the alignment shaft204of the front beam96is inserted into the shaft exposure hole216. Both ends in the axis direction are externally exposed in the width direction from each of the side plates121.

As shown inFIG. 8, the rear edge of the rear sidewall notch108on each of the rear sidewalls112is not exposed, when viewed from the side, relative to the rear edge of the notch179on each of the side plates121.

In the drum unit21assembled as above, each of the outward coupling insertion holes130formed on the left side plates121face the inward coupling insertion portion74on the left side of each of the drum subunits23in the width direction.

Moreover, a left cap180(see the hatched area in the drawing) is arranged in correspondence to each of the drum subunits23on the lower half of the left side plate121of the drum unit21. Each of the left caps180is formed as a sheet with a convex shape when viewed from the side. Each of the left caps180is made of insulating rubber or sponge. Each of the left caps180plugs a latching hole (not shown) to latch the wire spring127. Plugging the latching hole prevents foreign objects from entering through the latching hole, while exposing the drum shaft27, shaft hole124, outward coupling insertion hole130, and screw136.

As shown inFIG. 7, in the drum unit21, the grid electrode81and wire electrode80are externally exposed in the width direction from each of the center openings133that are formed on the right side plate121. The developer carrier electrode82is externally exposed in the width direction from each of the front openings134. A cleaning electrode83is externally exposed in the width direction from the rear opening135.

A right cap181(see the hatched area in the drawing) corresponds to each of the drum subunits23on the lower half of the right side plate121of the drum unit21. Each of the right caps181is formed as a sheet form with a convex shape when viewed from the side. Each of the right caps181is made of insulating rubber or sponge. Each of the right caps181plugs the center opening133, front opening134, and rear opening135, thereby preventing foreign objects from entering, while exposing the drum shaft27, developer carrier electrode82, wire electrode80, grid electrode81and cleaning electrode83.

In addition, the left cap180and right cap181have insulation properties. These insulating properties prevent the power supplied to each of the electrodes from leaking via the side plates121.

Using the procedures, the drum subunits23and drum unit21are assembled. As described above, the left side frame70cannot be assembled with the other parts (right side frame71and center frame72). Rather, the drum subunit23can be completed by assembling the center frame72(where the right side frame71is assembled) to the side plate121(where the left side frame70is assembled in advance).

As shown inFIG. 23, each of the left side frames70is arranged on the inside in the width direction relative to the left side plate121. Also, the internal wall of the left side plate121contacts the convex strip84of each of the left side frames70. Also, boss75of each left side frame70is fit into each of the light transmission holes123of the left side plate121so that the boss75is externally exposed in the width direction.

Next, the screwing portion85of each of the left side frames70faces the center screw insertion hole132that is located in front of each of the outward coupling insertion holes130on the left side plate121. The screw132is inserted into the center screw insertion hole132and screwed into the screwing portion85. By doing so, each of the left side frames70is assembled to the left side plate121. Next, the left side plate121(where each of the left side frames70is assembled), front beam96, rear beam111, and the right side plate121are assembled on each of the center frames72(where the right side frame70is assembled) as described above.

In contrast, as shown inFIG. 6, by arranging a multiplicity of drum subunits23and fitting the alignment projection200into the concave alignment portion202, the left side frame70of the drum subunit23can be assembled on the left side plate95of the drum subunit23in front. The side plate121can be assembled after installation of the multiple drum subunits23is completed, thereby allowing relatively easy assembly of the drum unit.

3. DEVELOPING CARTRIDGE

FIGS. 11 to 13show how the developing cartridge is constructed.

(1) Developing Cartridge

As shown inFIG. 11, in the developing cartridge22, the developer carrier34is arranged so that the developer carrier34is exposed downward from the opening36at the bottom edge of the developing frame31. In addition, the developer carrier shaft45of the developer carrier34is supported by both sidewalls141of the developing frame31in a rotatable manner. The developer carrier shaft45is arranged so that both ends of the developer carrier shaft45in the axis direction extend to both sidewalls141in the width direction. Furthermore, collar members50cover both ends of the developer carrier shaft45. The collar member50is formed in a hollow tube having a certain external diameter D (see the solid arrow inFIG. 11). The external diameter D is the same as or slightly smaller than the groove width B of the deepest portions153and154(seeFIG. 4). In addition, an inclined collar surface185is formed between the left side edge surface in the width direction and the peripheral surface of the collar50. The collar50is provided on the left end of the developer carrier45as an inclined surface. The collar50is chamfered to connect the above components.

A conductive feed member182is provided on the right side plate141of the developing cartridge22. The feed member182includes a bearing183and a cylinder184that externally (to the right) extend in the width direction from the top edge of the bearing183. The cylinder184is formed in a hollow tube shape having a certain external diameter E (see the broken line inFIG. 11). The cylinder184externally extends to the right in the width direction. The external (right side) edge surface in the width direction of the cylinder184is positioned on the right side (in the left and right direction) as compared to the external (right side) edge surface in the width direction of the collar member50on the right side in the width direction. Furthermore, the external diameter E is larger than the external diameter D of the collar50and the groove width B (seeFIG. 4) of the deepest portions153and154. The external diameter E is approximately the same or slightly smaller than the groove width A of the right guiding groove73(seeFIG. 4). The feed member182is attached on the developing frame31by the screw inserted in the axis direction (left and right direction) relative to the cylinder184(seeFIG. 15).

As shown inFIG. 13, the bearing183is formed in a thin rectangular plate shape when viewed from the side. A bearing hole188penetrates the bearing183in the thickness direction at the bottom edge. The bottom edge of the bearing183is positioned between the right sidewall141and the collar member50in the left and right direction. The developer carrier shaft45is inserted into the bearing hole188of the bearing183. The developer carrier shaft45is supported in a rotatable manner by both sidewalls141as well as bearing183.

As shown inFIG. 12, a releasing projection212is formed at the rear edge of the top edge of both sidewalls141of the developing frame31. The releasing projection212is formed in a hollow tube that externally projects in the width direction from both sidewalls141.

In addition, as shown inFIG. 13, an alignment projection217is formed on the position near the window142on both edges in the left and right direction of the front wall of the developing frame31.

The alignment projection217is a trapezoid shape when viewed from the side. The alignment projection217projects from the front wall of the developing frame31.

Windows142for detecting the remaining amount of toner are located in both sidewalls141of the developing frame31. These windows142permit the detection light (for optically detecting the remaining amount of toner in the toner container37) transmit in the width direction. The amount of toner is determined using an optical sensor173. Optical sensor173includes a light emitting element174and light receiving element175(seeFIG. 17).

As shown inFIG. 12, a gear mechanism (not shown) (covered by a gear cover143) is provided on the left sidewall141of the developing cartridge22. This gear mechanism includes a passive coupling gear144that externally projects (to the left side) in the width direction from the gear cover143. The gear mechanism also includes a gear train (not shown) that interacts with the passive coupling gear144.

The passive coupling gear144is cylindrical. A coupling insertion indentation187(having a figure eight shape when viewed from the side) is formed in a concave manner on the left edge from the left edge towards the right. Cogs (not shown) are located on the circumference of the right edge. The diameter of the passive coupling gear144is larger than the external diameter E of the cylinder184(seeFIG. 11).

As shown inFIG. 11, the passive coupling gear144faces the cylinder184of the feed member182in the width direction. More specifically, the center axis of the passive coupling gear144aligns with the center axis of the cylinder184in the front-back and top-bottom directions.

In addition, the passive coupling gear144has a larger diameter than that of the cylinder184. The passive coupling gear144projects externally in the width direction from the collar member50. The left edge surface of the passive coupling gear144projects so that the left edge surface is positioned slightly inside (right side) relative to the external (left side) edge in the width direction of the left guiding groove189, when the developing cartridge22is installed in the drum subunit23.

A cylinder cover186is located on the gear cover143corresponds to the passive coupling gear144. The cylinder cover186and the passive coupling gear144function as the driving input portion. The cylinder cover186is a hollow cylinder having an external diameter F (see dotted arrow in the drawing). The cylinder cover186projects from the left surface of the gear cover143towards the left. The external diameter F of the cylinder cover186is slightly larger than the external diameter of the passive coupling gear144. In other words, the external diameter F is larger than the external diameter E of the cylinder184. In addition, the external diameter F of the cylinder cover186is larger than the groove width A of the right guiding groove73. The external diameter F is approximately the same or slightly smaller than the groove width C of the left guiding groove189(seeFIG. 6). As shown inFIG. 12, the cylinder cover186covers the circumference of the passive coupling gear143. The left edge surface of the cylinder cover186is level with the left edge surface of the passive coupling gear144. The cylinder cover186is open toward the left side.

As described in a later section, the coupling input shaft145(see FIG.18)(which is a driving rotator provided in the main body casing2) is connected to the passive coupling gear144so that the coupling input shaft145and the passive coupling gear144do not rotate relative to each other. A driving force from the motor (not shown) is transmitted to the coupling input shaft145.

The gear train (not shown) includes an agitator driving gear that engages the rotary shaft41of the agitator32. The gear train also includes a supplying roller driving gear that engages with the supplying roller shaft43of the supplying roller33. The gear train further includes a developer carrier driving gear that engages the developer carrier shaft45of the developer carrier34. Finally, the gear train includes detection gear205and other gears. These gears of the gear train engage with the passive coupling gear144via intermediate gears, etc.

The detection gear205is supported in a rotatable manner by the detection gear supporting shaft (not shown). The detection gear supporting shaft externally projects (to the left side) in the width direction from the left sidewall141on the diagonal to the upper front of the passive coupling gear144.

This detection gear205is formed as a gear with missing cogs. The cog and missing cog portions (not shown) are provided on the right edge. On the left surface, a detected projection (not shown) is formed, where the detected projection is provided along the periphery of the detection gear205and projects towards the left side.

This detected projection (not shown) corresponds to the information on the developing cartridge22. Here, the information on the developing cartridge22is whether or not the developing cartridge22is new or old or the information on the number of printable pages for the developing cartridge22.

When the drum unit21(in which the developing cartridge22is mounted) is installed in the main body casing2, a driving force from the motor is transmitted to the cogs of the detection gear205via the input coupling shaft145and the passive coupling gear144. In response, the detection gear205rotates.

Along with the rotation of the detection gear205, the detected projection (not shown) of the detection gear205contacts one end of the lever206(seeFIG. 23). The level206is provided in the drum subunit23. Because of the detected projection, the lever206moves around the lever moving shaft207. Also, the other end of the lever206projects to the left from the lever transmission hole208of the side plate121(seeFIG. 8). The other end of the lever206is detected by the detection sensor (not shown) provided in the main body casing2. The detection results of the detection sensor (not shown) are, for example, the number of detections of the lever206and the time that is required for a single detection, and the CPU (not shown but in the main body casing) determines the information regarding the developing cartridge22.

A developing cartridge graspable portion146is provided on the developing frame31. The developing cartridge graspable portion146is formed in a long thin plate in the left and right direction. The developing cartridge graspable portion146is provided on the top wall147of the developing frame31.

In addition, the rotation shaft (not shown) is inserted on the rear edge of the developing cartridge graspable portion146. The rotation shaft is supported by the rear edge of the top wall147of the developing frame31via the rotary shaft (not shown).

The developing cartridge graspable portion146has a graspable long hole209in an approximate rectangular shape (when viewed from the side) at its center in the left and right direction.

As shown inFIG. 13, both edges in the left and right direction on the front edge of the developing cartridge graspable portion146and both edges in the left and right direction on the front edge of the top wall147that face with them are connected by a flexible member210. The flexible member210may be, for example, a coil spring, a plate spring, or a spring (for instance, a coil spring). The front edge of the developing cartridge graspable portion146is pressed in the direction away from the front edge of the top wall147.

A pressing projection211extends beyond the front edge of the developing cartridge graspable portion146.

(2) Installation of the Developing Cartridge to the Drum Unit

As shown inFIG. 9, to install the developing cartridges22for the various colors into the drum subunits23, the developing cartridge22is mounted down onto the drum subunit23.

More specifically, as shown inFIG. 15, the collar member50of the right edge in the axis direction of the developer carrier shaft45of the developing cartridge22and the cylinder184of the feed member182are inserted in the right guiding groove73(having been formed in the right side frame71of the drum subunit23). At the same time, as shown inFIG. 16, the collar member50(on the left edge in the axis direction of the developer carrier shaft45), passive coupling gear144, and the cylinder cover186(that covers the circumference of the passive coupling gear144) are inserted into the left guiding groove189formed between the left side frame70and the left side plate95of the center frame72of the corresponding drum subunit23. Then, developing cartridge22is pushed downward into the drum subunit23so that the cylinder184slides along the right guiding groove73. Also, cylinder cover186(covering passive coupling gear144) slides along the left guiding groove189. The insertion/removal direction of the developing cartridge22to/from the drum subunit23is in the top and bottom direction, as described above.

As shown inFIGS. 15 and 16, when the collar members50on both edges in the axis direction of the developing shaft45contact the deepest portion154of the right guiding groove73and the deepest portion153of the left guiding groove189, then the developing cartridge22is mounted on the corresponding drum subunit23.

As shown inFIG. 15, at this time, the collar member50on the right side in the axis direction and the groove wall that forms the groove width at the deepest portion154contact each other. As shown inFIG. 16, the collar member50on the left side in the axis direction and the groove wall that forms the groove width at the deepest portion153contact each other.

Each of the developing cartridges22contacts the alignment roller218of the drum subunit23(seeFIG. 9). The alignment projection217also contacts the alignment roller218(seeFIG. 10) of the front beam96. In addition, the rubber roller46of the developer carrier34contacts the surface of the image carrier24, as shown inFIG. 2.

The developing cartridge22is aligned with the drum subunit23when it is installed in the drum subunit23, through the contact of the collar member50with the deepest portions153and154, the contact of the alignment projection217with the alignment roller218, and the contact of the developer carrier34with the image carrier24.

More specifically, as shown inFIG. 16, the collar member50contacts the groove walls that face each other at the deepest portions153and154(seeFIG. 15). Therefore, the developing cartridge22is aligned relative to the drum subunit23in the direction that faces each of the groove walls of the deepest portions153and154(namely, the direction that connects the diagonal to the upper rear and the diagonal to the lower front).

When the alignment projection217contacts the alignment roller218, the developing cartridge22is aligned, relative to the drum subunit23, in the direction that connects the diagonal to the upper rear and the diagonal to the lower front.

When the developer carrier34contacts the image carrier24, the developing cartridge22is aligned in the direction where the developer carrier34contacts the image carrier24, in the direction that connects the diagonal to the lower rear and the diagonal to the upper front.

As a result, the developing cartridge22is aligned relative to the drum subunit23in the top and bottom direction.

In addition, as shown inFIG. 15, when the developing cartridge22is installed in the corresponding drum subunit23, the cylinder184of the feed member182of the developer carrier shaft45contacts the convex portion176of the feed coil155(that is connected to the developer carrier electrode82provided on the right side frame71).

Furthermore, as shown inFIG. 17, when the developing cartridge22is installed on the corresponding drum subunit23, the left window142that is embedded in the left sidewall141of the developing frame31faces the boss75(formed in the left side frame70) and the light transmission hole123(formed in the left side plate121). In addition, the right window142that is embedded in the right sidewall141of the developing frame31faces the boss75(formed in the right side frame71) and the light transmission hole123(formed on the right side plate121), in the width direction, so that the detection light can be transmitted. This alignment allows light to be transmitted through the developing frame.

In addition, as shown inFIG. 8, the passive coupling gear144(that projects from the gear cover143on the left sidewall141of the developing frame31) faces the coupling internal insertion portion74(located on the left side frame70) and the coupling external insertion hole130(located on the left side plate121), in the width direction. Here, the coupling input shaft145provided on the main body casing2(seeFIG. 18) can pass through freely in the forward and backward directions.

When all the developing cartridges22are inserted in the drum subunit23, the near-side graspable portion104of the front beam96, the developing cartridge graspable portion146of each of the developing cartridges22, and the far-side graspable portion116of the rear beam111overlap each other in the front and rear directions as shown inFIG. 14.

Furthermore, when all the developing cartridges22are inserted in the drum subunit23, each of the developing cartridges22can be withdrawn upwards, by inserting fingers into the graspable long hole209to grab the developing cartridge graspable portion146and then pulling upwards.

As shown inFIG. 1, after all the developing cartridges22are installed in the drum subunit23as described above and the drum unit21is installed in the drum housing161of the main body casing2, then a color image can be formed on the paper3through the above-described image formation operation.

4. MAIN BODY CASING

FIG. 18is a schematic view that shows the top view of the inside the laser printer shown inFIG. 1in order to explain the operation in which the passive coupling gear is connected to the coupling input shaft.FIG. 19is a left side perspective view of the coupling input shaft and around the arm in order to explain the contact condition between the coupling input shaft and the arm inFIG. 18.

The main body casing2has an approximately rectangular box shape (with a front opening when viewed from the side) and a drum housing161(housing the drum unit21) is formed within the main body casing2. In addition, a drum insertion/removal opening162that connects to the drum housing161is formed on the front wall of the main body casing2.

A front cover163to open/close the drum insertion/removal opening162is provided on the front wall of the main body casing2. This front cover163is supported by the hinge (not shown) provided at the bottom edge of the drum insertion/removal opening162of the main body casing2in a rotatable manner. By this arrangement, the hinge allows the front cover163to open and close the main body casing2. By doing so, when front cover is closed using the hinge as the point of support, the drum insertion/removal opening162is closed by the front cover163. When the front cover163is open using the hinge as the point of support, then the drum insertion/removal opening162is opened so that the drum unit21can be inserted/removed to/from the drum housing161from the front, via the drum insertion/removal opening162.

A roller (not shown) and a rail (not shown) are provided in the drum housing161. This rail (not shown) extends in the front and rear direction at the internal wall of both walls165that face the main body casing2in the width direction. The walls165face each other in the width direction. In addition the roller (not shown) is provided on the internal wall of both walls165in a rotatable manner above the front edge of each rail (not shown) with a slight gap from each rail.

Therefore, when the hook122of the side plate121is guided by the roller (not shown) and roll177is guided on the rail (not shown) the drum unit21is smoothly inserted/removed in the front and rear direction to/from the drum housing161.

In addition, an alignment bar (not shown), which is installed between the internal walls of both sidewalls165, is provided at the rear edge of the drum housing161. An alignment mechanism (not shown) is provided near the roller (not shown) at the front edge of the drum housing161. This alignment mechanism (not shown) selectively applies a backward (direction of the drum unit21installation) or a forward (direction of the drum unit21removal) pressure against the drum unit21that is contained in the drum housing161depending on the opening/closing of the front cover163.

More specifically, when drum unit21is installed in the drum housing161and the front cover is closed, the alignment shaft204of the drum unit21(seeFIG. 7) is pressed backward by the alignment mechanism (not shown). In addition, by doing so, the notch179of each side plate121(seeFIG. 7) contacts the alignment bar (not shown) of the drum housing161, and therefore the drum unit21is aligned inside the drum housing161by the alignment mechanism (not shown) and the alignment bar (not shown).

When the front cover163is open, the alignment mechanism (not shown) presses the alignment shaft204(seeFIG. 7) of the drum unit21forward. The notch179is released from the alignment bar (not shown). Next, the alignment of the drum unit21in the drum housing161is released. Now, the drum unit21can be removed from the drum housing161.

The drum unit21is inserted/removed to/from the drum housing161by grasping the near-side graspable portion104at the operation position. In addition, when the near-side graspable portion104rotates to the stowed position, the front cover163can be closed. It is acceptable to interlock the rotation of the near-side graspable portion104with the opening/closing of the front cover163.

A tray housing171containing the paper tray7is formed below the drum housing161of the main body casing2. In addition, a tray insertion/removal opening172that connects to the tray housing171is formed at the front wall of the main body casing2.

The paper tray7is mounted in the tray housing171so that the paper tray7can slide along the front and rear direction. When pulling the paper tray7toward the front when the paper tray7is mounted on the tray housing171, the paper tray7can be removed from the tray housing171.

Furthermore, as shown inFIG. 18, the left sidewall165may include an external wall192that forms the external (left side) surface in the width direction and an internal wall193that forms the internal (right side) surface in the width direction.

A coupling input shaft145(connected to the passive coupling gear144) may be provided on the left side of the developing cartridge22so that the developing cartridge22can move forward and backward in the width direction. An arm194that moves the coupling input shaft145forward and backward in the width direction (left and right direction) may be provided between the external wall192and internal wall193in the width direction.

The arm194includes an arm portion195(extending in the front and rear direction) and a cam196(provided at the rear edge of the arm portion195in an integrated manner).

As shown inFIG. 19, a long hole197that extends in the front and rear direction (where the coupling input shaft145is inserted) is provided on the cam196. A thick retreating area198(thick in the width direction) is provided around the rear edge of the long hole197. A thin advancing area199(thin in the width direction) is provided around the front edge of the long hole197.

The arm194is supported so that the arm194can move in the front and rear direction along the internal wall193under the condition in which the coupling input shaft145is inserted in the long hole197at the rear edge. In addition, the arm194moves in the front and rear direction by interlocking with the opening/closing of the front cover163.

As shown inFIGS. 18B and 18D, the coupling input shaft145faces the coupling insertion hole187of the passive coupling gear144of the drum unit21. A rotary driving force from a motor (not shown) provided in the main body casing2is applied to the coupling input shaft145. In addition, this coupling input shaft145is always pressed internally (right side) in the width direction (for example, toward the coupling insertion hole187).

During the insertion/removal of the drum unit21to/from the main body casing2, when the front cover7is opened, the arm194moves to the front by interlocking with the opening of the front cover163and as shown inFIG. 19B. The safe area198is engaged with the coupling input shaft145. Then, as shown inFIGS. 18B and 18D, the coupling input shaft145retreats from the coupling insertion hole187of the passive coupling gear144to the left side (outside in the width direction) in the rotary axis direction of the coupling input shaft145(width direction or left and right direction) by being placed against the pressure from the spring (not shown).

After the installation of the drum unit21to the main body casing2, when the front cover7is closed, the arm194interlocks with the closing of the front cover163and moves backwards. As shown inFIG. 19A, the advance area199is engaged with the coupling input shaft145. Then, as shown inFIGS. 18A and 18C, the coupling input shaft145advances on the right side (inwards in the width direction) towards the coupling insertion hole187of the passive coupling gear144. The coupling input shaft145is connected in a relatively non-rotatable manner.

By doing so, at each of the developing cartridges22, the driving force from the motor (not shown) is transmitted to/from the coupling input shaft145to the passive coupling gear144. Accordingly, the agitator21, supplying roller33, developer carrier34, and detection gear205are rotary driven via the gear train (not shown).

In addition, as shown inFIG. 7, terminals that are connected to the high voltage substrate (not shown) are connected to the wire electrode80, grid electrode81(exposed from each of the center openings133which are formed on the right side plate121), developer carrier electrodes82(exposed from each of the front openings134), and the cleaning electrode83(exposed from the rear opening135).

In addition a pressing release mechanism, not shown in the drawing, is provided on top of the drum housing161of the main body casing2. The pressing release mechanism (not shown) allows the color printer1to selectively form color images (using the four drum subunits23) and a monochrome image (using only the black drum subunit23K) depending on the user's objectives.

More specifically, when the drum unit21is inserted in the drum housing161, the front cover163is closed and the coupling input shaft145is connected to the passive coupling gear144. Next, the selection of whether the image formation is carried out in color or monochrome is carried out by operating the operation panel (not shown).

Depending on this selection, when a color image formation is carried out, the pressing release mechanism (not shown) downwardly presses the pressing projections211of the four developing cartridges22that are mounted on the drum unit21. At this time, the graspable portion146of each developing cartridge, where the pressing projections211are provided, moves towards the front edge of the top wall147of the developing frame31relative to the pressure of the flexible member210. Along with this movement, the pressure by the flexible member210acts on the front edge of the top wall147of the developing frame31in the direction of releasing from the front edge of the developing cartridge graspable portion146(downward). Because of this, the developing frame31of the four developing cartridges22moves downward. Also, the rubber rollers46of the developer carrier34(supported by each of the developing frames31) is pressed against the surface of the image carrier24, as shown inFIG. 2. Thus, the toner from each of the developer carriers34is supplied to each of the image carriers24allowing the formation of a color image.

When a monochrome image formation is carried out, as shown inFIG. 7, the pressing release mechanism (not shown) presses downward only on the pressing projection211of the black developing cartridge22K among the four developing cartridges22mounted on the drum unit21. In contrast, the pressing release mechanism (not shown) presses upward on the releasing projections212at the developing cartridges22that are not the black developing cartridge22K. Because of this the black developing cartridge22K moves downwards, rubber roller46of the developer carrier34of the black developing cartridge23K is pressed against the surface of the image carrier24of the black drum subunit23K, the developing cartridges22, other than the black developing cartridge22K, move upward, and the rubber rollers46of the developer carrier34of each of the developing cartridges22are released from each of the image carriers24. Therefore, the toner is supplied only to the image carrier24of the black drum subunit23K from the developer carrier34of the developing cartridge22K thereby allowing the formation of a monochrome image.

In addition, if paper jams in the middle of the image formation, the pressing release mechanism (not shown) supplies an upward pressure to the release projections212of all the developing cartridges22. By doing so, the rubber roller46of the developer carriers34of all the developing cartridges22are released from the image carrier24allowing easy removal of the jammed paper3.

In addition, as shown inFIG. 17optical sensors173for detecting the remaining amount of toner contained in the toner container37and that correspond to each of the developing cartridges22are provided in the main body casing2.

Each of the optical sensors173includes light emission element174and light receiving element175. The light emission elements174and light receiving elements175face each other over the drum unit21(light emission element174on the right side and light receiving element175on the left side).

Light emission element174and light receiving element175are arranged so that they face with a pair of light transmission holes123in the width direction on the outside in the width direction of the pair of light transmission holes123under the condition in which the corresponding developing cartridge22is installed in the drum unit21and the drum unit21is installed in the drum housing171.

Because of this, the detection light emitted from the light emitting element174passes through the boss75that fits in the right light transmission hole123, and then is incident in the toner container37via the right window142. The light then passes through the toner container37and then is emitted via the left window142. Finally, the light passes through the boss75(that is fit in the left light transmission hole123). The light is finally is detected by the light detection element175.

The optical sensor173detects the remaining amount of toner in the toner container37in correspondence to the detection frequency of the detection light. When the remaining amount of the toner in the toner container37becomes scarce, the toner empty warning is indicated on the operation panel, etc. (not shown).

The color laser printer1includes a passive coupling gear144and feeder member182in the developing cartridge22. The drum subunit23includes a right side frame71(that forms the right guiding groove73), a center frame72, and a left side frame70(that forms the left guiding groove189).

When the passive coupling gear144is connected to the coupling input shaft145, a driving force from a motor is securely supplied to the developer carrier34via the gear train (not shown).

In addition, when the cylinder184of the feeder member182contacts the feed coil155(provided on the drum subunit23), electric power is supplied to the developer carrier34(and is known as developing bias). Compared to the case in which the feed coil155is provided somewhere other than at the drum subunit23, the cylinder184can come closer to the feed coil155. This movement allows a secure supply of electric power to the developer carrier34. Further, the size of the cylinder184can be reduced.

Moreover, the passive coupling gear144is guided so that the passive coupling gear144slides on the left guiding groove189. Also, the cylinder184of the feeder member182is guided so that the cylinder184slides on the right guiding groove73. By this action, the developing cartridge22is inserted/removed to/from the drum subunit23.

This arrangement allows easy replacement of the developing cartridge22. Further, the function of guiding the developing cartridge22to the drum subunit23during the installation by the left guiding groove189can be added to the passive coupling gear144. This is in addition to the original function of the passive coupling gear144, which is the function of transmitting a driving force from the coupling input shaft145. In addition, the function of being guided by the right guiding groove73during the installation of the developing cartridge22to the drum subunit23can be added to the cylinder184. The original function of the cylinder184is to supply electric power from the feed coil155.

Therefore, a new element does not need to be provided assist the guiding of the left guiding groove189and right guiding groove73.

Consequently, the functionality of the developing cartridge22and the color laser printer1is improved. Further, the size of the color laser printer1can be reduced.

A drum unit21, with drum subunits23with image carriers24and associated developing cartridges22mounted, can be inserted/removed to/from the drum housing161of the main body casing2in the rotary axis direction of the coupling input shaft145. The rotary axis direction is the front and rear direction being perpendicular to the width (left and right) direction.

Therefore, multiple developing cartridges22and drum subunits23allow an image formation in multiple colors. In addition, when an image carrier24needs to be replaced, the replacement may be easily performed based on the easy insertion/removal of the multiple developing cartridges22and drum subunits23.

In addition, the coupling input shaft145can move forward and backward in the rotary axis direction (left and right direction).

Therefore, when the coupling input shaft145is engaged with the advance area199of the arm194, the coupling input shaft145advances to the right towards the coupling insertion hole187of the passive coupling gear144. The coupling input shaft145is also connected so as to be relatively non-rotatable. In addition, when the coupling input shaft145is engaged with the retreating area198of the arm194, the coupling input shaft145retreats to the left from the coupling insertion hole187. Accordingly, the connection of the coupling input shaft145with the passive coupling gear144is released.

The connection and disconnection between the passive coupling gear144and the coupling input shaft145may be interlocked with the opening/closing of the front cover163during the insertion/removal of the drum unit21to/from the drum container161of the main body casing2. This may improve the usability of the color laser printer1.

Consequently, the functionality of the color laser printer1can be improved.

Furthermore, the circumference of the passive coupling gear144is covered by the cylinder cover186. Thus, the passive coupling gear144can avoid direct contact with the left guiding groove189when guided by the left guiding groove189. This may reduce the risk of collision damage to the passive coupling gear144.

As a result, the developing cartridge22can be securely installed in the drum subunit23in an insertable/removable manner.

Moreover, the developing cartridge22is arranged so that the developer carrier34is downwardly exposed, downstream of the direction of installation of the developing cartridge22into the drum subunit23. The developer carrier34may be exposed from the opening36at the bottom of the developing frame31. Both ends of the developer carrier shaft45of the developer carrier34are covered with the collar member50.

The developing cartridge22is aligned relative to the drum subunit23during the installation to the drum sub unit23when the collar member50contacts the deepest portion153of the left guiding groove189and the deepest portion154of the right guiding portion73. This allows the the developing cartridge22to be installed in the drum subunit23with high precision. In addition, the collar member50is arranged adjacent to the developer carrier shaft45on the downstream side in the installation direction. The developer carrier34can securely and stably contact the image carrier24.

Thus, when the drum subunit23is installed in the main body casing2, the coupling input shaft145can be securely connected to the passive coupling gear144. Thus, a driving force can be securely transmitted to the developer carrier34. In addition, the feed coil155can securely contact the cylinder184of the feeder member182, thereby allowing a secure supply of electric power to the developer carrier34.

When the collar member50carries out alignment of the developing cartridge22relative to the drum subunit23during installation, alignment of the developer carrier34(as both ends of the developer carrier shaft45are covered by the collar member50) can be carried out with high precision.

As a result, the developing cartridge22can be accurately installed to the drum subunit23. In addition, covering both ends with collar member50allows a reduction of the damage to the developer carrier shaft45. Moreover, the length of the developer carrier shaft45can be reduced.

Between the left edge surface and the circumference of the collar50of the developer carrier shaft45, an inclined collar surface185is formed with a chamfered edge.

Therefore when the developing cartridge22is inserted/removed to/from the drum subunit23, the friction generated by the contact between the left edge of the collar member50and the left guiding groove189of the drum subunit23can be reduced.

This allows developing cartridge22to move smoothly in the insertion/removal direction to/from the drum subunit23. This allows secure installation of developing cartridge22to the drum subunit23in an insertable/removable manner.

The passive coupling gear144externally projects (to the left) from the collar member50in the width direction (left and right direction). The width direction is the direction perpendicular to the insertion/removal direction of the developing cartridge22to/from the drum subunit23. In addition the cylinder cover186is level with the left edge surface of the passive coupling gear144.

The passive coupling gear144and the cylinder cover186(covering the circumference of the passive coupling gear144) can come close to the coupling input shaft145. Thus, when the drum subunit23is inserted in the main body casing2, the passive coupling gear144can securely connect to the coupling input shaft145. This allows a driving force to be securely transmitted to the developer carrier34.

Furthermore, as shown inFIGS. 18C and 18D, the left edge surface of the passive coupling gear144projects slightly inside (compared to the external (left side) edge) of the left guiding groove189when the developing cartridge22is installed in the drum unit23. This is in comparison to the positions shown inFIGS. 18A and 18B(where the left edge surface of the passive coupling gear144is positioned on the inner side (right side) relative to the inside (right side) in the width direction of the left guiding189. With respect toFIGS. 18C and 18D, the movement of the coupling input shaft145in the rotary axis direction (left and right direction) in order to connect to the passive coupling gear144can be minimized.

Accordingly, when the amount of movement of the coupling input shaft145in the present embodiment is X (see the arrow inFIG. 18D) and the amount of movement of the coupling input shaft145in the comparative example is Y (see arrow inFIG. 18B), the size of the main body casing2in the rotary axis (width) direction of the coupling input shaft145can be reduced by the amount Z. The amount Z is equivalent to the difference between the amount of movement Y and the amount of movement X. Therefore, the size of the color laser printer1can be reduced.

The cylinder184of the feeder member182externally projects (to the right) in the width direction. The edge surface of the outside (right side) in the width direction of the cylinder184is on the right compared to the edge surface of the outside (right side) in the width direction of the collar member50.

Therefore, the cylinder184can come closer to the feed coil155. This allows a secure supply of electric power to the developer carrier34.

The passive coupling gear144has a larger diameter than that of the cylinder184. This larger diameter provides greater rigidity of the passive coupling gear144compared to the cylinder184.

As a result, the driving force from the input coupling shaft145can be stably transmitted to the passive coupling gear144.

In addition, the passive coupling gear144faces the cylinder184in the width direction. More specifically the center axis of the passive coupling gear144matches the center axis of the cylinder184in the front and rear, and top and bottom directions.

Therefore, when the developing cartridge22is installed in the drum subunit23, a driving force from the input coupling shaft145is transmitted to the passive coupling gear144. This prevents a large influence from torsion on the cylinder184and the feeder member182, even if such torsion was generated and centered at the passive coupling gear144.

As a result, a positional error of the feeder material182can be prevented. Here, the feed coil155contacts the cylinder184, thereby allowing a stable supply of electric power to the developer carrier34.

In addition, both the passive coupling gear144(covered by cylinder cover186) and the cylinder184of the feeder member182are guided individually by the right guiding groove73and left guiding groove189during the insertion/removal of the developing cartridge22to/from the drum subunit23. The developing cartridge can be stably inserted/removed to/from the drum subunit23without losing its alignment with the rest of the system.

Consequently, this arrangement allows a secure installation of the developing cartridge22to the drum subunit23in an insertable/removable manner.

The groove width C of the left guiding groove189is larger than the groove width A of the right guiding groove73. The external diameter E of the cylinder184guided by the right guiding groove73is approximately the same or slightly smaller than the groove width A of the right guiding groove73. The external diameter F of the cylinder cover186(guided by the left guiding groove189and covering the passive coupling gear144) is larger than the groove width A of the right guiding groove73. The external diameter F is approximately the same or slightly smaller than the groove width C of the left guiding groove189.

Based on such a structure, the passive coupling gear144and the cylinder cover186are smoothly guided by the left guiding groove189. Also, the cylinder184is smoothly guided by the right guiding groove73.

When the passive coupling gear144and cylinder cover186face the right guiding groove73and the cylinder184faces the left guiding groove189, the passive coupling gear144and cylinder cover186are not guided by the right guided groove73. Accordingly, the developing cartridge22cannot be installed to the drum subunit23. Therefore, an incorrect installation of the developing cartridge22to the drum subunit23can be prevented.

Consequently, this arrangement ensures proper installation of the developing cartridge22to the drum subunit23.

6. MODIFIED EXAMPLES

FIG. 20shows a left lateral view of the drum subunit and developing cartridge for which a Modified Example 1 is applied. Modified Example 1 shows the state in which the developing cartridge is inserted into/removed from the drum subunit.FIG. 21is a right lateral view of the drum subunit and developing cartridge in which Modified Example 1 is applied. The right guiding groove is exposed for description purposes and to show the state in which the developing cartridge is inserted into/removed from the drum subunit.

InFIGS. 20 and 21, common elements described previously are labeled with the same numerals. Description for these common elements is omitted.

As shown inFIGS. 15 and 16, in this embodiment, the developing cartridge22is aligned relative to the drum subunit23during the installation to the drum subunit23, when 1) the collar member50contacts the deepest portions153and154, 2) the alignment projection217contacts the alignment roller218, and 3) the developer carrier34contacts the image carrier24.

In such an embodiment, as a modified example, the cylinder cover186(covering circumference of the passive coupling gear144and the cylinder184of the feeder member182) performs an aligning role instead of the aligning role performed by collar member50. In that case, the external diameter of the collar member50can be smaller than the external diameter D (compare to the diameter of collar member50inFIG. 11).

In that case, as shown inFIG. 20, the bottom edge of the front concave portion69projects towards the rear side perpendicular wall138at the left guiding groove189. The amount of projection is configured so that the space between the bottom edge of the front concave portion69and the top edge of the rear concave portion152is smaller than the external diameter F of the cylinder cover186. Additionally, the top edge of the rear concave portion152is positioned diagonally to the upper rear of the bottom edge of the front concave portion69.

In addition, as shown inFIG. 21, a concave alignment portion220that is continuously concave from the rear side groove wall to the rear of the right guiding groove73is formed at the location where the rear side groove wall of the right guiding groove73faces the cylinder184when the developing cartridge22is installed in the drum subunit23.

In such a drum subunit23, as shown inFIG. 21A, the collar member50of the right edge in the width direction of the developer carrier45of the developing cartridge22and the cylinder184of the feeder member182are inserted in the right guiding groove73. At the same time, as shown inFIG. 20B, the collar member50of the left edge in the width direction of the developer carrier45, passive coupling gear144, and the cylinder cover186that covers the circumference of the passive coupling gear144are inserted in the left guiding groove189. Then, the developing cartridge22is pushed downwards to the drum subunit23so that the cylinder184slides along the right guiding groove73. Also, the cylinder cover186that covers the passive coupling gear144slides along the left guiding groove189.

Then, as shown inFIG. 21B, the cylinder184of the feeder member182diagonally contacts the upper bottom of the convex portion176of the feed coil155. Because of this the cylinder184is pressed diagonally towards the upper rear (toward the alignment concave portion220from the feed coil155). Also, the cylinder184is engaged at the edge of the alignment concave portion220.

As shown inFIG. 20A, the distance between the top edge of the rear concave portion152and the bottom edge of the front concave portion69is smaller than the external diameter F of the cylinder cover186. Therefore, the passive coupling gear144(whose circumference is covered by the cylinder cover186) is engaged at the top edge of the rear concave portion152and the bottom edge of the front concave portion69. At that time the passive coupling gear144(whose circumference is covered by the cylinder cover186) receives pressure from the top edge of the rear concave portion152and the bottom edge of the front concave portion69in the direction that connects diagonally to the upper rear and diagonally to the lower front.

At this time, the collar member50is positioned at the deepest portions153and154. Nonetheless, the collar member50does not contact the deepest portions153and154.

As described above, when the cylinder184contacts the feed coil155and is engaged at the top edge of the alignment concave portion220, and when the passive coupling gear144(whose circumference is covered by the cylinder cover186) is engaged at the top edge of the rear concave portion152and the bottom edge of the front concave portion69, the developing cartridge22is aligned against the drum subunit23in the direction that connects diagonally to the upper rear and diagonally to the lower front. This alignment direction is identical to the alignment direction when the collar member50is used for alignment.

Therefore, the cylinder184and the passive coupling gear144may align the developing cartridge22relative to the drum subunit23instead of the collar member50.

An alignment function of the developing cartridge22relative to the drum subunit23can be added in addition to the original functions for the passive coupling gear144and cylinder184of the feeder member182. Namely, the function to transmit a driving force from the coupling input shaft145at the passive coupling gear144and the function to feed electric power when the cylinder184contacts the feed coil155may be added.

As a result, the functionality of a developing cartridge22and color laser printer1can be improved.

FIG. 24is a left perspective view of the developing cartridge in which Modified Example 2 is applied showing the back side of the developing cartridge. InFIG. 24, common elements described previously are labeled with the same numerals. Description for these common elements is omitted.

As shown inFIG. 24, in this developing cartridge22, the circumference of the passive coupling gear144can be externally exposed. More specifically, left edge of the cylinder cover186matches the right edge of the collar member50in the left and right direction.

In other words, the circumference of the portion of the passive coupling gear144that is on the left of the left edge of the cylinder cover186is not covered by the cylinder cover186. Because of this arrangement, when the developing cartridge22is inserted/removed to/from the drum subunit23, the circumference of the passive coupling gear144slides on the left guiding groove189instead of sliding on the cylinder cover186.

FIG. 25is a left perspective view of the developing cartridge in which Modified Example 3 is applied, showing the backside of the developing cartridge. InFIG. 25, common elements described previously are labeled with the same numerals. Description for these common elements is omitted.

As shown inFIG. 25, in this developing cartridge22, the circumference of the passive coupling gear144can be covered by the cylinder cover186so that the passive coupling gear144has a gap in the diameter direction relative to the internal circumference of the cylinder cover186.

In addition, a pair of coupling connection projections119(facing each other over the rotary axis of the passive coupling gear144) can be formed so that they project to the left side from the left surface of the passive coupling gear144on the passive coupling gear144instead of the coupling insertion hole187.

The coupling connection projections119are formed so that their left edge matches the left edge of the cylinder cover186in the left and right direction. On the right edge surface (the surface that faces the passive coupling gear144in the left and right direction) of the coupling input shaft145that connects to the passive coupling gear144, a figure eight-shaped insertion hole (not shown) is formed (the insertion hold being a concave shape from the right edge surface to the left). Therefore, when each of the coupling connection projections119are inserted into the insertion holes (not shown) for the coupling input shaft145, the coupling input shaft145is connected to the passive coupling gear144.

FIGS. 26,27and28are left perspective views of the developing cartridge in which Modified Example 4 is applied, showing the back side of the developing cartridge. InFIGS. 26,27and28, common elements described previously are labeled with the same numerals. Description for these common elements is omitted.

As shown inFIG. 26, in this developing cartridge22, the entire circumference of the passive coupling gear144does not need to be covered by the cylinder cover186. More specifically, only a part of the circumference of the passive coupling gear144(which slides on the left guiding groove189during insertion and removal) is covered by the cylinder cover186.

In other words, the cylinder cover186is formed as a pair of projections in an arch shape when viewed from the side that sandwiches the passive coupling gear144in the front and rear direction. This arch shape is in contrast to a cylinder shape. The cylinder cover186slides on the left guiding groove189when the developing cartridge22is inserted/removed to/from the drum subunit23. Therefore, the cylinder cover186is acceptable as long as the cylinder cover186has a minimum size that allows sliding on the left guiding groove189instead of the passive coupling gear144. As shown inFIG. 27, the length of the circumference of the cylinder cover186can be, for example, approximately half of the cylinder cover186shown inFIG. 26. Furthermore, as shown inFIG. 28, the length of the circumference of the cylinder cover186can be, for example approximately half of the cylinder cover186shown inFIG. 27.

The drum unit21according to the above embodiments has a separate drum subunit23so that the developing cartridges22are mounted on each of the drum subunits23in an insertable/removable manner. Nonetheless, the developing cartridge22and drum subunit23can be formed in an integrated manner. That allows replacement of the toner that corresponds to each color, developer carrier34, and image carrier24together by replacing the drum unit21.

The above embodiments show examples of a tandem-type color laser printer1in which a transfer of an image is directly carried out from each of the image carriers24to the paper3. Nonetheless, aspects of the present invention are not limited to the above tandem-type laser printer. For example, the laser printer1can be a color laser printer with an intermediate transfer-type system in which the toner image in each color can be transferred to a transfer body from each of the photoconductors temporarily. Next, the combined toner images are transferred to the paper at the same time. In addition, the laser printer can be formed as a monochrome laser printer. The monochrome laser printer can include a process unit (the image forming unit) in which a single developing cartridge22is mounted on a single drum subunit23.

Although the subject matter has been described in language specific to structural features and/or mechanical acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. Numerous other embodiments, modifications, and variations within the scope and spirit of the appended claims will occur to persons of ordinary skill in the art from a review of this disclosure.