Image forming device having process unit that can be pulled out thereof

The process unit includes a casing, a developer unit, and a switching unit. The developer unit is movable between an image-forming position and a detached position. The developer unit includes a drive force input unit and a drive force transmitting unit. A drive force is inputted into the drive force input unit from outside of the developer unit. The drive force transmitting unit transmits the drive force. The switching member is for switching the drive force transmitting unit between a transmitting state and an interrupting state. The switching member switches the drive force transmitting unit to the transmitting state when the developer unit is at the image-forming position, and the switching member switches the drive force transmitting unit to the interrupting state when the developer unit is at the detached position.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2010-042724 filed Feb. 26, 2010. The entire content of this priority application is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a process unit provided in a laser printer or other image-forming device and the image-forming device equipped with this process unit.

BACKGROUND

A tandem-type color laser printer is well known in the art as a type of electrophotographic color printer. The tandem-type color laser printer has a plurality of photosensitive drums juxtaposed in a prescribed direction and provided one for each of the toner colors yellow, magenta, cyan, and black, and a plurality of developer cartridges respectively corresponding to the photosensitive drums for supplying toner to the photosensitive drums.

One type of tandem-type color laser printer includes a main casing, a drum unit detachably provided in the main casing and provided with the photosensitive drums, and the developer cartridges provided with developing rollers and detachably mounted in the drum unit. In the color laser printer, bosses are provided on each developer cartridge, and pressing members are provided in the drum unit for pressing the bosses provided on the developer cartridge.

In order to mount the developer cartridge in the drum unit, the developer cartridge is pushed downward into the drum unit until the developing roller held in the developer cartridge contacts the corresponding photosensitive drum in the drum unit so that the developer cartridge is positioned at a detached position. Next, the developer cartridge is tilted forward so that the bosses on the developer cartridge slide underneath the pressing members and the developer cartridge is positioned at an image-forming position. At this time, the pressing members suppress the bosses, pressing the developing roller to the photosensitive drum, thereby completing the operation for mounting the developer cartridge in the drum unit.

SUMMARY

In the color laser printer described above, the developing roller is fixed in position relative to the photosensitive drum when the developer cartridge has been pushed into the drum unit and the developing roller has contacted the photosensitive drum, i.e., when the developer cartridge is positioned at the detached position.

Even if the drum unit is mounted into the main casing of the printer while the developer cartridge is at the detached position, but not at the image forming position (if the developer cartridge is not tilted forward after being inserted into the drum unit), a drive force supplied from the main casing may be inputted into the developer cartridge. When this occurs, the drive force can cause damage to the developer cartridge since the developer cartridge is not at the image forming position.

Therefore, it is an object of the present invention to provide a process unit and an image forming device capable of preventing damage to the developer cartridge when the drive force is inputted into the developer cartridge while the developer cartridge is at the detached position (i.e., not fully mounted).

In order to attain the above and other objects, the invention provides a process unit. The process unit includes a casing, a developer unit, and a switching unit. The developer unit is detachably mounted in the casing and is movable between an image-forming position and a detached position. An image forming operation can be performed when the developer unit is at the image-forming position. The developer unit can be detached from the casing when the developer unit is at the detached position. The developer unit includes a developing member, a drive force input unit, and a drive force transmitting unit. A drive force is inputted into the drive force input unit from outside of the developer unit. The drive force transmitting unit transmits the drive force inputted into the drive force input unit. The switching member is provided on the casing for switching the drive force transmitting unit between a transmitting state in which the drive force is transmitted and an interrupting state in which transmission of the drive force is interrupted. The drive force is inputted into the drive force input unit regardless of whether the developer unit is positioned at the image-forming position or the detached position. The switching member switches the drive force transmitting unit to the transmitting state when the developer unit is at the image-forming position, and the switching member switches the drive force transmitting unit to the interrupting state when the developer unit is at the detached position.

According to another aspect, the present invention provides an image forming device. The image forming device includes a process unit and a drive source. The process unit includes a casing, a developer unit, and a switching unit. The developer unit is detachably mounted in the casing and is movable between an image-forming position and a detached position. An image forming operation can be performed when the developer unit is at the image-forming position. The developer unit can be detached from the casing when the developer unit is at the detached position. The developer unit includes a developing member, a drive force input unit, and a drive force transmitting unit. A drive force is inputted into the drive force input unit from outside of the developer unit. The drive force transmitting unit transmits the drive force inputted into the drive force input unit. The switching member is provided on the casing for switching the drive force transmitting unit between a transmitting state in which the drive force is transmitted and an interrupting state in which transmission of the drive force is interrupted. The drive force is inputted into the drive force input unit regardless of whether the developer unit is positioned at the image-forming position or the detached position. The switching member switches the drive force transmitting unit to the transmitting state when the developer unit is at the image-forming position, and the switching member switches the drive force transmitting unit to the interrupting state when the developer unit is at the detached position. The drive source inputs the drive force to the drive force input unit.

DETAILED DESCRIPTION

1. Overall Structure of a Color Laser Printer

The color laser printer1is a direct tandem color laser printer of a horizontal type, whereby photosensitive drums for forming individual colors are juxtaposed horizontally in a tandem arrangement. The color laser printer1includes a main casing2, a sheet-feeding unit3provided in the main casing2for feeding sheets of a paper P to be printed, and an image-forming unit4for forming images on the paper P supplied by the sheet-feeding unit3.

(1) Main Casing

The main casing2has a substantially rectangular box shape in a side view for accommodating the sheet-feeding unit3and the image-forming unit4. A front cover5is provided on one side wall of the main casing2. The front cover5is capable of pivoting relative to the main casing2about its lower end and, thus, can be opened to allow mounting and removing a process unit9described later.

In the following description, the side of the main casing2on which the front cover5is provided (the right side inFIG. 1) will be called the “front side,” and the opposite side (the left side inFIG. 1) will be called the “rear side.” Further, the left and right sides of the main casing2will be based on the perspective of an operator looking at the printer1from the front side. In other words, the near side inFIG. 1will be the “left side,” while the far side inFIG. 1will be the “right side.”

The sheet-feeding unit3includes a paper tray6for accommodating paper P. The paper tray6is detachably mounted in the bottom section of the main casing2. A pair of registration rollers7is disposed above the front end of the paper tray6.

The paper P accommodated in the paper tray6are fed toward the registration rollers7one sheet at a time, and the registration rollers7convey the paper P toward the image-forming unit4(between photosensitive drums14and a conveying belt22described later) at a prescribed timing.

The image-forming unit4includes a scanning unit8, the process unit9, a transfer unit10, and a fixing unit11.

(3-1) Scanning Unit

The scanning unit8is disposed in the top section of the main casing2. As indicated by solid lines inFIG. 1, the scanning unit8irradiates laser beams toward four photosensitive drums14, described later, based on image data for selectively exposing the photosensitive drums14.

(3-2) Process Unit

(3-2-1) Structure of the Process Unit

The process unit9is disposed in the main casing2below the scanning unit8and above the transfer unit10. The process unit9includes a process frame12, and four developer cartridges13provided for each of the four printing colors. The process unit9can be mounted in and removed from the main casing2by sliding in the front-to-rear direction.

The process frame12is disposed in the main casing2and can be pulled out of the main casing2in a forwardly direction. The process frame12retains the photosensitive drums14, Scorotron chargers15, and drum cleaning rollers16.

The four photosensitive drums14are arranged parallel to each other with their axes extending in the left-to-right direction and are spaced at intervals in the front-to-rear direction. The photosensitive drums14specifically include, in order from front to rear, a black photosensitive drum14K, a yellow photosensitive drum14Y, a magenta photosensitive drum14M, and a cyan photosensitive drum14C.

The Scorotron chargers15are positioned diagonally above and rearward of the respective photosensitive drums14. The Scorotron chargers15face the respective photosensitive drums14but are separated therefrom.

The drum cleaning rollers16are disposed on the rear side of the respective photosensitive drums14, confronting and contacting the same.

Each of the developer cartridges13is removably mounted in the process frame12above corresponding photosensitive drum14so as to confront the photosensitive drum14. The developer cartridges13specifically include, in order from front to rear, a black developer cartridge13K, a yellow developer cartridge13Y, a magenta developer cartridge13M, and a cyan developer cartridge13C. Each of the developer cartridges13is also provided with a developing roller17.

As will be described later, the developing roller17is rotatably supported in the lower end of the developer cartridge13so that the peripheral surface of the developing roller17is exposed on the rear side (FIG. 4). The developing roller17opposes and contacts the upper front edge of the corresponding photosensitive drum14(FIG. 1).

Each developer cartridge13further includes a supply roller18for supplying toner to the developing roller17and a thickness-regulating blade19for regulating the layer thickness of toner supplied to the developing roller17. The developer cartridge13also has an interior space in the upper section for accommodating the toner of a corresponding color.

(3-2-2) Developing Operations of the Process Unit

The toner accommodated in the developer cartridge13is supplied onto the supply roller18, and the supply roller18in turn supplies the toner to the developing roller17. The toner is positively tribocharged between the supply roller18and the developing, roller17.

As the developing roller17rotates, the thickness-regulating blade19regulates the thickness of the toner supplied to the developing roller17so that the developing roller17carries a uniform thin layer of the toner on the surface thereof.

In the meantime, the Scorotron charger15applies a uniform positive charge to the surface of the photosensitive drum14as the photosensitive drum14rotates. Subsequently, the scanning unit8irradiates laser beams (indicated by solid lines inFIG. 1), exposing the surfaces of the respective photosensitive drums14in a high-speed scan to form electrostatic latent images on the surfaces of the photosensitive drums14corresponding to an image to be formed on the paper P.

As the photosensitive drum14continues to rotate, the positively charged toner carried on the surface of the developing roller17is supplied to the electrostatic latent image formed on the surface of the photosensitive drum14. The toner develops the latent image into a visible toner image by reversal.

(3-3) Transfer Unit

The transfer unit10is disposed inside the main casing2above the sheet-feeding unit3and below the process unit9. The transfer unit10extends in the front-to-rear direction. The transfer unit10includes a drive roller20, a follow roller21, the conveying belt22, and four transfer rollers23.

The drive roller20and the follow roller21are disposed in parallel to each other and separated in the front-to-rear direction.

The conveying belt22is looped around the drive roller20and the follow roller21and is positioned so that an upper portion of the conveying belt22confronts and contacts each of the photosensitive drums14from above. When the drive roller20is driven to rotate, the conveying belt22circulates so that the upper portion in contact with the photosensitive drums14moves rearward.

Each of the transfer rollers23is disposed within the inner space defined by the conveying belt22at a position opposing the corresponding photosensitive drum14through the upper portion. The position between each photosensitive drum14and the corresponding transfer roller23will be called a “transfer position.”

When the paper P is supplied from the sheet-feeding unit3onto the conveying belt22, the conveying belt22conveys the paper P rearward so that the paper P passes sequentially through the transfer positions between the photosensitive drums14and the respective transfer rollers23. As the conveying belt22conveys the paper P, toner images of the respective colors are sequentially transferred from the photosensitive drum14onto the paper P to form a color image thereon.

In some cases, toner remains on the surface of the photosensitive drum14after the toner image has been transferred from the photosensitive drum14to the paper P. This residual waste toner is transferred to the corresponding drum cleaning roller16by a cleaning bias applied to the drum cleaning roller16when the waste toner carried on the rotating photosensitive drum14opposes the drum cleaning roller16, and the drum cleaning roller16retains the waste toner.

(3-4) Fixing Unit

The fixing unit11is positioned on the rear side of the transfer unit10. The fixing unit11includes a heating roller24and a pressure roller25disposed in confrontation with the heating roller24. After the color image is transferred onto the paper P, the color image is fixed to the paper P by heat and pressure as the paper P passes between the heating roller24and the pressure roller25in the fixing unit11.

(4) Sheet Discharge

A U-shaped conveying path is formed in the main casing2on the downstream side of the fixing unit11in the sheet conveying direction and leads from the fixing unit11to a sheet-discharge tray27formed above the scanning unit8. Pairs of discharge rollers26are provided along the U-shaped path. After the toner image has been fixed to the conveying paper P in the fixing unit11, the discharge rollers26convey the paper P along the U-shaped conveying path and discharge the paper P onto the sheet-discharge tray27.

2. Detailed Description of the Process Unit

(1) Process Frame

As shown inFIG. 2, the process frame12has a substantially rectangular frame-like shape elongated in the front-to-rear direction in a plan view. The process frame12is provided with a pair of left and right side plates31.

The left and right side plates31are arranged parallel to each other and separated in the left-to-right direction. As illustrated inFIGS. 3(a) and3(b), both left and right side plates31are formed in a substantially rectangular shape elongated in the front-to-rear direction.

Each of the left and right side plates31has four guide grooves32(FIG. 3(b)) formed therein.

In the preferred embodiment, a construction related to a process-side actuator41described later and a switching boss42described later is provided only for the left side plate31. Below, the left side plate31will be described in detail, while a description of the right side plate31will be omitted. In the following description, the left side plate31will simply be referred to as the “side plate31.”

The four guide grooves32evenly spaced in the front-to-rear direction are formed in the right surface (inner surface with respect to the left-to-right direction) of the side plate31and respectively corresponding to the photosensitive drums14. Each of the guide grooves32extends downward from the upper edge of the side plate31in a rearward sloping direction, i.e., in a first sloping direction X indicated by a solid arrow inFIG. 3(b), and is substantially U-shaped with the top portion open in the upper edge of the side plate31. The guide groove32is formed on the upper front side of the corresponding photosensitive drum14.

More specifically, four pairs of guide ribs33are formed on the right surface of the side plate31for defining the respective guide grooves32. Each pair of individual guide ribs33includes a front rib33F on the front side and back rib33B on the rear side.

The guide ribs33are separated from each other in the front-to-rear direction and extend along the first sloping direction X while protruding outward toward the right. The lower ends of the guide ribs33are opposite to and away from the corresponding photosensitive drum14by a small gap.

The front rib33F extends from the upper edge of the side plate31in a substantially straight line along the first sloping direction X, and then curves rearward and extends in a second direction Y indicated by a dotted arrow inFIG. 3(b), which is a direction following a radial direction of the photosensitive drum14.

The back rib33B extends from the upper edge of the side plate31in a substantially straight line along the first sloping direction X, and then protrudes rearward in an arc shape so as to slightly increase the width of the guide groove32(distance between the front rib33F and the back rib33B in the front-to-rear direction). The bottom end of the back rib33B is opposite to the lower end of the front rib33F with a gap therebetween that is substantially equivalent to the diameter of a developing roller shaft73(described later). The lower edge of the back rib33B extends along the second sloped direction Y.

In other words, each guide groove32is configured of a first guide groove32A extending from the upper edge of the side plate31along the first sloping direction X, and a second guide groove32B in continuous communication with the first guide groove32A and extending from the bottom end of the first guide groove32A along the second sloped direction Y.

The side plate31is formed with a coupling hole37at a position between each front rib33F and the arc-shaped part of the corresponding back rib33B.

The coupling hole37is an elongated hole extending along a direction sloping downward toward the rear. Through the coupling hole37, a coupling member58(described later) of the developer cartridge13is exposed on the left side of the side plate31.

An extension part34is provided on the right surface of the side plate31between each pair of adjacent guide grooves32, and also extending forward from the front side of the forwardmost guide groove32.

Each extension part34extends in the front-to-rear direction and connects the top edge of the front rib33F forming the guide groove32on the rear side with the top edge of the back rib33B forming the guide groove32on the front side except the forwardmost extension part34which is connected only to the top edge of the front rib33F forming the guide groove32on the rear side. A recession35is concave downward and is formed in the top surface of each extension part34.

The right surface of the side plate31is provided with the pressing cams36, process-side actuators41, and the switching bosses42.

The four pressing cams36are provided on the upper edge of the side plate31at positions corresponding to the guide grooves32and upwardly adjacent to the respective extension parts34.

Each pressing cam36is substantially fan-shaped in a side view. Specifically, each pressing cam36includes a pair of flat portions38, and a curved portion39. The distance between the pair of flat portions38expands gradually in a direction upward and rearward toward the curved portion39. The curved portion39connects the upper rear ends of the flat portions38and has a substantially arc shape that expands outward in a direction diagonally upward and rearward.

The pressing cam36also has a rotational shaft40extending outward from the pressing cam36in left and right directions near the area at which the lower front ends of the two flat portions38are joined. Right end of the rotational shaft40is supported in the inner surfaces of the left side plate31, whereby the pressing cam36is rotatably supported about the rotational shaft40. An urging member (not shown) is provided for urging the pressing cam36counterclockwise in a left-side view.

The four process-side actuators41are provided above the back ribs33B and corresponding to the developer cartridges13. Each process-side actuator41is substantially rod-shaped and is rotatably disposed on the side plate31so that one end of the process-side actuator41protrudes rightward from the right surface of the side plate31(FIGS. 3(b) and7(b)), while the other end of the process-side actuator41is exposed on the left side of the side plate31(FIG. 3(a)). When the one end of the process-side actuator41is contacted by a detection gear63(FIG. 3(b), described later) of the developer cartridge13, the process-side actuator41rotates, causing the other end of the process-side actuator41to protrude from the left surface of the side plate31.

The four switching bosses42are provided on the side plate31above the process-side actuators41and corresponding to the developer cartridges13(FIG. 3(b)). Each switching boss42is formed substantially like a square column that protrudes outward from the right surface of the side plate31. The switching boss42is disposed farther rearward than the one end of the corresponding process-side actuator41so as not to interfere with the detection gear63(described later) of the developer cartridge13when the developer cartridge13is at an image-forming position (described later) and so as to interfere with the detection gear63when the developer cartridge13is at a detached position (described later).

(2) Developer Cartridge

As shown inFIGS. 1 and 4(a), each developer cartridge13includes a frame51, in addition to the developing roller17and the supply roller18described above.

The frame51has a box shape elongated in the left-to-right direction. In a side view, the frame51is shaped substantially like an isosceles triangle with a vertex pointing diagonally downward and rearward.

A handle52and a pair of left and right bosses53are provided in the top front portion of the frame51. An opening54is formed in the bottom rear side of the frame51.

The handle52is disposed in the left-to-right center of the frame51and is elongated in the left-to-right direction. The handle52is formed to protrude upward from the top edge of the frame51.

The bosses53are substantially cylindrical in shape and protrude outward in the left and right directions from the respective left and right endfaces of the frame51. The opening54is formed across the entire left-to-right dimension of the frame51, opening toward the rear. The frame51is also provided with a drive unit55.

As shown inFIGS. 4(a) and4(b), the drive unit55is disposed on the left end of the frame51and includes the coupling member58, a detection gear56, and a gear cover57.

The coupling member58is a female coupling member having a substantially cylindrical shape. The coupling member58is rotatably provided on the lower rear end of the developer cartridge13. As shown inFIG. 4(b), the coupling member58is integrally configured of a large-diameter gear part64and a small-diameter coupling part65extending coaxially from the left side of the large-diameter gear part64.

When the developer cartridge13is mounted in the main casing2, a male coupling member (not shown) provided in the main casing2couples with the left end of the small-diameter coupling part65from the left side thereof. Through this coupling, a motor81(described later with reference toFIGS. 6 and 8) provided in the main casing2can input a drive force to the small-diameter coupling part65.

As shown inFIGS. 4(b) and7(a), the gear train56includes an idler gear61, an agitator gear62, and the detection gear63. The idler gear61is disposed above the coupling member58. The idler gear61is a two-stage gear formed integrally of a large diameter part on the outside and a small-diameter part on the inside (FIG. 4(b)). The large diameter part is engaged with the coupling member58from above.

The agitator gear62is disposed slightly above and forward of the idler gear61and is engaged with the small-diameter part of the idler gear61on the top front side. The agitator gear62is fixedly provided on the left end of a rotational shaft of an agitator (not shown) serving to agitate the toner in the developer cartridge13and is not capable of rotating relative to the rotational shaft.

The detection gear63is a sector gear disposed above the agitator gear62(FIG. 7(a)). More specifically, the detection gear63has gear teeth on approximately four-fifths of its circumference and no teeth on the remaining approximately one-fifth. The detection gear63is provided with a support part67and two contact parts66.

The support part67is a substantially cylindrical shape and protrudes leftward from the left surface of the detection gear63(FIG. 4(b)). As shown inFIG. 7(a), the support part67includes an arc-shaped part68, a corner part69, and a recess part69a.The arc-shaped part68is a substantially semicircular shape and centered on the rotational axis of the detection gear63. The corner part69connects one end of the arc-shaped part68and protrudes outward along the radial direction of the detection gear63opposite to the toothless region of the detection gear63. The recess part69aconnects the other end of the arc-shaped part68and is depressed inwardly in the radial direction.

Each contact part66is substantially plate-shaped, extends radially outward from the approximate radial center of the detection gear63, and protrudes leftward from the left edge of the support part67. The contact parts66are positioned on opposing sides of the corner part69approximately 120 degrees apart in the circumferential direction of the detection gear63. The number and shape of the contact parts66corresponds to information about the developer cartridge13(information indicating whether the developer cartridge is new, the number of sheets that can be printed with the developer cartridge, etc.).

The detection gear63is rotatably provided on the frame51, with the corner part69pointing upward and the toothless region of the detection gear63facing downward.

The drive unit55is further provided with a coil spring70as shown inFIG. 7(a). The coil spring70is wound about a support boss71that protrudes leftward from the left side of the frame51, with one end fixed to the left wall of the frame51and the other end contacting the corner part69from the upper front side. With this construction, the coil spring70urges the detection gear63counterclockwise in a left-side view.

Consequently, the detection gear63is normally engaged with the agitator gear62through the gear teeth formed farther rearward than the toothless region in a left-side view. Accordingly, the gear train56is maintained in a transmitting state in which the drive force inputted into the small-diameter coupling part65of the coupling member58can be transmitted to the detection gear63.

As shown inFIG. 4(a), the gear cover57includes a coupling cover76xand a detection gear cover77. The coupling cover76has a substantially cylindrical shape and extends leftward from the left surface of the gear cover57near the lower edge thereof for encircling the coupling member58.

The detection gear cover77is semicylindrical in shape and extends leftward from the left surface of the gear cover57for accommodating the detection gear63. In a side view, the detection gear cover77is substantially semicircular in shape and is closed on its endface. An exposure opening72is formed in the rear portion of the detection gear cover77for exposing the contact protrusion66.

The developing roller17is disposed in the lower end of the frame51, with its axis extending in the left-to-right direction. The rear circumferential surface of the developing roller17is exposed through the opening54. The developing roller17also includes the developing roller shaft73. Collar members75are fitted over each of the left and right ends of the developing roller shaft73.

The developing roller shaft73is inserted through the developing roller17in the left-to-right direction and serves as the axial center of the developing roller17. A developing roller drive gear59is fixedly provided on the left end of the developing roller shaft73and cannot rotate relative to the developing roller shaft73. Collar members75are provided on both left and right ends of the developing roller shaft73.

The collar members75are a substantially cylindrical shape and elongated in the left-to-right direction. The inner diameter of the collar members75is formed slightly larger than the outer diameter of the developing roller shaft73. The collar members75are fitted over the ends of the developing roller shaft73.

As shown inFIG. 1, the supply roller18is disposed diagonally above and forward of the developing roller17and contacts the top front circumferential portion of the developing roller17. The supply roller18is also provided with a supply roller shaft74(FIG. 7(a)).

The supply roller shaft74is inserted through the supply roller18in the left-to-right direction and serves as the axial center of the supply roller18. A supply roller gear60is fixedly provided on the left end of the supply roller shaft74and cannot rotate relative to the supply roller shaft74.

As shown inFIG. 4(b), the developing roller17is rotatably supported in the frame51by rotatably supporting the left end of the developing roller shaft73in the left side of the frame51and by rotatably supporting the right end of the developing roller shaft73in the right side of the frame51. The developing roller drive gear59is engaged with the large-diameter gear part64of the coupling member58from below.

The supply roller18is rotatably supported in the frame51by rotatably supporting the left end of the supply roller shaft74in the left side of the frame51and by rotatably supporting the right end of the supply roller shaft74in the right side of the frame51. The supply roller gear60is engaged with the large-diameter gear part64of the coupling member58from the lower front side thereof (FIG. 7(a)).

(1) Mounting and Removal of Developer Cartridges Relative to the Process Unit

In order to mount the developer cartridges13in the main casing2, the developer cartridges13are first mounted in the process frame12as shown inFIG. 2.

To mount the developer cartridge13in the process frame12, the operator first grips the handle52of the developer cartridge13and positions the developer cartridge13above the process frame12, which has been pulled out from the main casing2, so as to be aligned with the corresponding photosensitive drum14in the front-to-rear direction.

Next, the operator lowers the developer cartridge13into the process frame12.

As the developer cartridge13is inserted into the process frame12, the left end of the developing roller shaft73is fitted into the top portion of the first guide groove32A formed in the left side plate31and the right end of the developing roller shaft73is fitted into the top portion of the first guide groove32A formed in the right side plate31.

As the left and right ends of the developing roller shaft73are guided along the first guide grooves32A of the guide grooves32, the developer cartridge13is inserted into the process frame12along the first sloping direction X (FIG. 3(b)), i.e., downward along a slightly rearward slope.

After the left and right ends of the developing roller shaft73reach the lower ends of the first guide grooves32A, the operator continues to insert the developer cartridge13into the process frame12.

At this time, the left and right ends of the developing roller shaft73are guided along the second guide grooves32B. Accordingly, the left and right ends of the developing roller shaft73are guided into the deepest portions of the second guide grooves32B along the second sloped direction Y (FIG. 3(b)), i.e., downward along a more pronounced rearward slope.

Through this operation, the developer cartridge13is disposed in the detached position in which the developer cartridge13can be removed from the process frame12as shown inFIG. 5(a).

At this time the bosses53are in contact with the curved portions39of the pressing cams36on the rear sides thereof. That is, through pressure applied by the curved portions39of the pressing cams36to the bosses53, the developer cartridge13is held in the process frame12with its front end lifted in a direction upward and rearward so that the developer cartridge13is tilted rearward. In this state, as shown inFIG. 6, the coupling member58of the developer cartridge13is exposed through the coupling hole37formed in the process frame12.

Hence, when the process unit9is mounted in the main casing2in this state (i.e., when the developer cartridge13is in the detached position), the male coupling member (not shown) of the main casing2is fitted into the coupling member58, enabling the drive force from the motor81to be inputted into the coupling member58, as indicated by the two-dotted chain line inFIG. 6.

At the same time, as illustrated inFIGS. 5(a) and5(b), while the developer cartridge13is mounted in the process frame12as described above, one of the contact parts66of the detection gear63is in contact with the switching boss42of the process frame12from above.

As the developer cartridge13is pushed downward, the switching boss42applies upward pressure to the contact part66. Consequently, the detection gear63rotates clockwise in a left-side view against the urging force of the coil spring70.

When the developer cartridge13is in the detached position, the toothless region of the detection gear63is positioned opposite the agitator gear62so that the detection gear63and the agitator gear62are not engaged. Since the detection gear63and the agitator gear62are disengaged, the gear train56cannot relay the drive force between the detection gear63and the agitator gear62. Hence, when the developer cartridge13is placed in the detached position, the gear train56is switched to an interrupting state in which the drive force cannot be transmitted.

Since the contact part66of the detection gear63is contacting the top of the switching boss42at this time, the switching boss42restricts the contact part66from contacting the process-side actuator41positioned lower than the switching boss42. That is, when the developer cartridge13is at the detached position, the switching boss42is positioned between the contact part66and the process-side actuator41and prevents the contact part66from contacting the process-side actuator41(FIG. 5(b)).

Next, the operator pivots the developer cartridge13forward while gripping the handle52.

As a result, as shown inFIG. 7(a), the developer cartridge13pivots forward about the developing roller shaft73, and the bosses53push the corresponding pressing cams36forward and slide beneath the pressing cams36as the pressing cams36are rotated clockwise in a left-side view.

When the bosses53slide beneath the pressing cams36, the pressing cams36engage the bosses53from above, and the force of urging members (not shown) pushes the bosses53in a direction diagonally downward and rearward.

At this time, the developer cartridge13is pushed by the pressing cams36in a direction diagonally downward and rearward, and the developing roller shaft73is guided by the second guide grooves32B of the side plate31. Thus, the developer cartridge13is pressed to the photosensitive drum14from above along the second sloped direction Y.

When the developer cartridge13is pivoted forward, the detection gear63is retracted forward from the switching boss42, removing the contact between the detection gear63and the switching boss42.

Accordingly, the urging force of the coil spring70rotates the detection gear63counterclockwise in a left-side view.

When gear teeth on the upstream side of the toothless region of the detection gear63with respect to the rotating direction of the detection gear63(counterclockwise in a left-side view) engage with the agitator gear62, the rotation of the detection gear63halts.

When the detection gear63and the agitator gear62are engaged, the gear train56can transmit the drive force between the detection gear63and the agitator gear62. Hence, when the developer cartridge13is placed in the image-forming position for forming images as shown inFIG. 7(a), the gear train56is switched to the transmitting state and can transmit the drive force.

Through this procedure, the developer cartridge13is placed in the image-forming position, and the operation for mounting the developer cartridge13in the process frame12is complete. All developer cartridges13are mounted in the process frame12according to the same procedure.

In order to remove a developer cartridge13from the process frame12, the operation for mounting the developer cartridge13in the process frame12is simply reversed in order. That is, the operator first grips the handle52and pivots the developer cartridge13rearward. While still gripping the handle52, the operator then pulls the developer cartridge13upward to remove the developer cartridge13from the process frame12.

(2) Mounting and Removal of the Process Unit Relative to the Main Casing

Next, the process unit9having all developer cartridges13mounted in the process frame12is mounted in the main casing2.

In order to mount the process unit9in the main casing2, the operator inserts the process unit9into the main casing2in a rearward direction. As shown inFIG. 1, when the process unit9is completely inserted into the main casing2, each of the photosensitive drums14contacts the upper portion of the conveying belt22.

Next, the operator pivots the front cover5upward and rearward to close the front cover5. The operation for mounting the process unit9in the main casing2is completed. To remove the process unit9from the main casing2, the operator pivots the front cover5forward and downward and simply pulls the process unit9in a forward direction from the main casing2.

(3) Drive Force Transmission

As shown inFIG. 8, when the process unit9is mounted in the main casing2, the male coupling members (not shown) provided in the main casing2are fitted into the corresponding coupling members58from the left side. At this time, the motor81inputs the drive force into the coupling members58and a warming-up operation is initiated.

In the warming-up operation, the drive force inputted into the coupling member58is transmitted to the detection gear63via the idler gear61and the agitator gear62(FIG. 7(a)). In other words, the gear train56transmits the drive force inputted into the coupling member58.

The drive force inputted into the coupling member58is also transmitted to the developing roller drive gear59and the supply roller gear60for rotating the developing roller17and the supply roller18, respectively.

When the drive force is transmitted to the detection gear63, the detection gear63rotates counterclockwise in a left-side view. As the detection gear63rotates, one of the contact parts66contact the one end of the process-side actuator41from above, causing the other end of the process-side actuator41to protrude from the process frame12.

A photosensor (not shown) provided in the main casing2detects the protrusion of the process-side actuator41, and a CPU (not shown) determines information related to the usage status of the developer cartridge13, such as whether the developer cartridge13is a new cartridge and the number of sheets that can be printed by the developer cartridge13, based on these detection results. Hence, the detection gear63specifies information related to the usage of the developer cartridge13when displaced counterclockwise in a left-side view.

After the detection gear63has rotated counterclockwise in a left-side view at a prescribed distance (four-fifths of a complete rotation corresponding to the periphery of the detection gear63with gear teeth), the toothless region of the detection gear63has rotated opposite the agitator gear62, and consequently the detection gear63comes into a halt. At this time, the end part of the coil spring70is recessed in the recess part69a.

If the used developer cartridge13is mounted in the process frame12, the end part of the coil spring70is recessed in the recess part69aand the toothless region of the detection gear63comes opposite to the agitator gear62. Thus, the detection gear63does not rotate even if the agitator gear62rotates. The CPU determines whether the developer cartridge13is new based on whether the detection gear63has rotated after mounted in the frame12.

4. Operations and Effects

(1) With the process unit9of the preferred embodiment illustrated inFIGS. 5(a) and7(a), when the developer cartridge13is placed in the detached position (FIG. 5(a)), the switching boss42applies pressure to the detection gear63, disengaging the detection gear63from the agitator gear62and switching the gear train56of the developer cartridge13to the interrupting state. Further, when the developer cartridge13is shifted from the detached position to the image-forming position (FIG. 7(a)), the urging force of the coil spring70engages the detection gear63with the agitator gear62, switching the gear train56of the developer cartridge13to the transmitting state.

Hence, when the developer cartridge13is in the detached position, the gear train56can prevent transmission of the drive force inputted into the coupling member58of the developer cartridge13.

This construction can prevent damage to the developer cartridge13that is caused when the drive force is inputted into the coupling member58of the developer cartridge13while the developer cartridge13is in the detached position.

(2) With the process unit9according to the preferred embodiment shown inFIG. 5(a), the switching boss42applies pressure to the detection gear63of the gear train56, reliably switching the gear train56into the interrupting state.

(3) Further, the gear train56can be switched to the interrupting state by rotating the detection gear63, as shown inFIG. 5(a). Accordingly, the gear train56can be switched to the interrupting state without greatly displacing the detection gear63.

(4) With the process unit9according to the preferred embodiment shown inFIG. 7(a), the coil spring70urges the detection gear63to engage with the agitator gear62. Accordingly, when the pressure applied by the switching boss42to the detection gear63is removed, the urging force of the coil spring70engages the detection gear63with the agitator gear62, switching the gear train56to the transmitting state. As a result, the gear train56can reliably be switched to the transmitting state when the pressure applied by the switching boss42to the detection gear63is removed.

(5) With the process unit9according to the preferred embodiment shown inFIG. 5(a), a plurality of gears (the idler gear61, the agitator gear62, and the detection gear63) in the gear train56is engaged with each other for transmitting the drive force. When the switching boss42disengages the detection gear63from the agitator gear62, the gear train56is switched to the interrupting state. Hence, by using the simple structure of the switching boss42for disengaging the detection gear63from the agitator gear62, the gear train56can be reliably switched to the interrupting state.

(6) With the process unit9according to the preferred embodiment shown inFIG. 5(a), the switching boss42disengages the detection gear63from the agitator gear62. Hence, transmission of the drive force to the detection gear63can be interrupted using a simple construction. This construction can prevent damage to the detection gear63when the drive force is inputted into the coupling member58of the developer cartridge13while the developer cartridge13is in the detached position.

(7) Further, the relative positions of the detection gear63provided on the developer cartridge13and the process-side actuator41provided on the process unit9change when the developer cartridge13is in the detached position (FIG. 6) and when the developer cartridge13is in the image-forming position (FIG. 8). Consequently, if the contact part66contacts the process-side actuator41while the developer cartridge13is in the detached position, the contact part66may press against the process-side actuator41in an abnormal direction and potentially cause damage to the process-side actuator41.

However, with the process unit9according to the preferred embodiment shown inFIG. 5(b), the switching boss42is disposed between the contact part66of the detection gear63and the process-side actuator41of the process frame12when the developer cartridge13is in the detached position, preventing the contact part66from contacting the process-side actuator41. Hence, this structure can reliably prevent the contact part66from contacting the process-side actuator41while the developer cartridge13is in the detached position and, thus, can prevent damage to the process-side actuator41through such contact.

(8) As shown inFIG. 1, the tandem-type process unit9is provided with a plurality of photosensitive drums14arranged parallel to each other in tandem and spaced at intervals, and the developer cartridges13corresponding to the photosensitive drums14. With the structure described in the preferred embodiment, the process unit9can prevent damage to the developer cartridge13when the drive force is inputted into the coupling member58of the developer cartridge13while the developer cartridge13is in the detached position.

(9) Since the color laser printer1according to the preferred embodiment is provided with the process unit9described above, the color laser printer1can prevent damage to the developer cartridge13by the drive force inputted from the motor81into the coupling member58of the developer cartridge13while the developer cartridge13is in the detached position.

5. Modification of the Embodiment

According to the preferred embodiment described above, the detection gear63of the developer cartridge13is configured of a sector gear having the toothless region. When the developer cartridge13is mounted in the process frame12, the detection gear63is rotated by pressure from the switching boss42so that the toothless region of the detection gear63is positioned opposite the agitator gear62. Consequently, the gear train56is switched from the transmitting state to the interrupting state.

However, as shown inFIGS. 9(a) and9(b), when employing a detection gear92according to a modification of the embodiment, the gear train56can be switched from the transmitting state to the interrupting state by sliding the detection gear92along the left-to-right direction. In the modification, like parts and components are designated with the same reference numerals to avoid duplicating description.

More specifically, the detection gear92is capable of sliding in the left and right directions (an axial direction of the detection gear92). When the detection gear92is slid leftward, an agitator gear91engages with the detection gear92(FIG. 9(a)). When the detection gear92is slid rightward, the agitator gear91is disengaged from the detection gear92(FIG. 9(b)).

A compression spring93is provided for urging the detection gear92leftward. A switching boss90is disposed in a position for contacting the rotational shaft of the detection gear92on the left side thereof when the developer cartridge13is in the detached position (FIG. 9(b)).

When mounting the developer cartridge13in the process frame12, the developer cartridge13is placed in the detached position. At this time, the switching boss90contacts the left side of the rotational shaft of the detection gear92and slides the detection gear92rightward against the urging force of the compression spring93. Consequently, the detection gear92is disengaged from the agitator gear91, switching the gear train56into the interrupting state.

When the developer cartridge13is placed in the image-forming position, the switching boss90is separated from the rotational shaft of the detection gear92, allowing the urging force of the compression spring93to slide the detection gear92leftward (FIG. 9(a)). Consequently, the detection gear92is engaged with the agitator gear91, switching the gear train56to the transmitting state.

According to the modification of the embodiment, the gear train56including the detection gear92and the agitator gear91is switched to the interrupting state when the switching boss90pushes the rotational shaft of the detection gear92rightward. Hence, the detection gear92and the agitator gear91can be reliably disengaged by sliding the detection gear92rightward, preventing damage to the detection gear92.

In the preferred embodiment described above, the gear train56is switched from the transmitting state to the interrupting state by disengaging the detection gear63from the agitator gear62, but the method of switching the gear train56according to the present invention is not limited to this particular combination of gears. For example, the gear train56may be switched to the interrupting state by disengaging the idler gear61and the agitator gear62.