Image forming apparatus having mechanism for allowing photosensitive drum and developing roller to contact during insertion of cartridge-mounted drawer

A cartridge has a first frame supporting a photosensitive member and a second frame supporting a developer carrying member. The first and second frames can take either a contact position where the two members are in contact with each other or a separated position where the two members are separated. A supporting member supporting the cartridge is movable between a mount position in a housing and a pull-out position outside the housing. When the supporting member is held in the pull-out position, the first and second frames are retrained in the separated position. The cartridge is supported on the supporting member to be movable between a first position where image formation is disabled and a second position where image formation is enabled. The cartridge is moved from the first position to the second position attendant to the movements of the supporting member from the pull-out position to the mount position.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2011-096552 filed Apr. 22, 2011. The entire content of the priority application is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an electrophotographic image forming apparatus.

BACKGROUND

Electrophotographic printers have been known and used in various fields. Typically, such a printer accommodates a photosensitive drum and a developing roller. To print an image on a recording medium, an electrostatic latent image is formed on the photosensitive drum. The developing roller is held in pressure contact with the photosensitive drum to supply toner to the photosensitive drum and develop the electrostatic latent image with the toner. The toner image is transferred onto and thermally fixed on the recording medium.

When the printer of the typed described above is shipped while holding the developing roller in pressure contact with the photosensitive roller, the developing roller may be deformed during transportation or movement to the custody. When the printer with the deformed developing roller is used for printing by an end user, the printed image would be defective.

Japanese Patent Application Publication No. 2002-40905 discloses a mechanism for temporarily separating the developing roller from the photosensitive drum. In the printer disclosed in Japanese Patent Application Publication No. 2002-40905, a process cartridge is mounted in the printer body. The process cartridge includes a drum unit and a developing unit, in which both units are combined to form the process cartridge and normally held in an urged state. The outer wall of the drum unit is formed with a hole, and the outer wall of the developing unit with a dowel extending into the hole of the drum unit to engage therewith. The engagement of the dowel with the hole restricts the movements of the developing unit relative to the drum unit, and the developing roller can be held in spaced-apart from the photosensitive drum.

The dowel-hole engagement mechanism is configured to disengage the dowel from the hole when the process cartridge is mounted in the printer body. The process cartridge needs to be pushed into the printer body to mount it therein with stronger pushing force than force required to mount a process cartridge with no dowel-hole engagement mechanism. In other words, with the process cartridge having the dowel-hole engagement mechanism, additional force is needed to disengage the dowel from the hole. As the stronger pushing force is needed, it may be difficult for a certain user to mount the process cartridge in the printer body.

When the dowel-hole engagement mechanism disclosed in Japanese Patent Application Publication No. 2002-40905 is applied to a color printer having a plurality of process cartridges corresponding to a plurality of colors of toner, the user is imposed upon far more difficulty in mounting the plurality of process cartridges in the color printer body. The difficulty may invite such a problem that disengagement of the dowel from the hole is not accomplished during mounting of the process cartridges. If such a problem occurs, printing cannot be performed even if the process cartridges are believed to be properly mounted in the color printer.

SUMMARY

In view of the foregoing, it is an object of the invention to provide an image forming apparatus which facilitates mounting of a cartridge while minimizing damages of the components contained in the cartridge.

In order to attain the above and other objects, the invention provides an image forming apparatus having such a basic configuration as to include a housing, a cartridge, a supporting member, and a separation releasing mechanism. The cartridge has a first frame, a second frame, and a separation retaining member. The first frame is configured to support a photosensitive member. The second frame is configured to support a developer carrying member carrying developer thereon to supply the developer onto the photosensitive member. The first frame and the second frame are engaged so as to move relative to each other between a contact position where the developer carrying member and the photosensitive member are in contact with each other and a separated position where the developer carrying member and the photosensitive member are separated. The separation retaining member is configured to retain the first frame and the second frame in the separated position. The supporting member is configured to support the cartridge to be movable between a first position where image formation with the developer is disabled and a second position where image formation with the developer is enabled. The supporting member is movable between a mount position in the housing and a pull-out position outside the housing. The separation releasing mechanism is configured to move the cartridge from the first position to the second position and disable the separation retaining member attendant to movements of the supporting member from the pull-out position to the mount position.

DETAILED DESCRIPTION

A color printer1shown inFIG. 1is one example of an image forming apparatus of the invention. The color printer1is of an intermediate image transfer type in which a toner image is once transferred onto the intermediate image transfer belt and the image thereon is finally transferred onto a sheet of paper P. A sheet of paper P is one example of a recording medium on which the image is formed. Throughout the specification, the terms “upper”, “lower”, “right”, “left”, “front”, “rear” and the like will be used assuming that the color printer1is disposed in an orientation in which it is intended to be used.

As shown inFIG. 1, the color printer1includes a housing2within which a sheet supplying section3and an image forming unit4are provided. The sheet supplying section3is provided for feeding a sheet of paper P toward the image forming unit4where images are formed on the sheet of paper P.

The housing2is substantially of a box-shape as viewed from right or left side. The image forming unit4is housed in the housing2. A front cover5is provided in the front wall of the housing2. Opening of the front cover5allows a drawer frame12(to be described later) to slidably move out of the housing2.

It should be noted that the side in which the front cover is provided (right side in the drawing) is the front side of the color printer1whereas the opposite side (left side in the drawing) is the rear side of the color printer1. The right side of the housing1as viewed from the front side is far side inFIG. 1whereas the left side of the housing1as viewed from the front side1is near side inFIG. 1.

A pair of registration rollers7is disposed at a position above the rear end portion of the sheet feed tray6. The topmost sheet of paper P stacked in the sheet tray8is fed toward the registration rollers7. The registration rollers7feed the sheet of paper P at a prescribed timing into a nip between the image forming unit4(intermediate image transfer belt22to be described later) and a secondary image transfer roller19(to be described later).

The image forming unit4includes a scanner unit8, a process unit9, a transfer unit10, and a fixing unit11. The scanner unit8is disposed above the sheet tray6. The scanner unit8irradiates laser beams onto photosensitive drums16as indicated by solid lines inFIG. 1to expose the photosensitive drums16to light based on image data.

The process unit9is disposed on above the scanner unit8and includes the drawer frame12and four process cartridges13. The drawer frame12is reciprocally movable in a direction from front to rear or rear to front (hereinafter referred to as “front-to-rear direction”) between a mount position (seeFIG. 1) in the housing2and a pull-out position (seeFIG. 8) outside the housing2. The drawer frame12can be drawn from the housing2to the pull-out position to facilitate replacement of the used process cartridge13with a new one. The process cartridges13are detachably mounted on the drawer frame12and arranged in parallel with one another with spacing between adjacent two process cartridges13. The process cartridges13are arranged in the drawer frame12so that the longitudinal axis of each process cartridge13is orthogonal to the direction from the mount position to the pull-out position. In this embodiment, black process cartridge13K, yellow process cartridge13Y, magenta process cartridge13M and cyan process cartridge13C are arranged in the stated order in the drawer frame12.

Each process cartridge13includes a drum unit (first frame)14and a developing unit (second frame)15. The drum unit14is configured to rotatably support the photosensitive drum16. The photosensitive drum16is substantially a cylindrical shape extending in the left-to-right direction and rotatably movably supported above the drum unit14. The photosensitive drum16is exposed to light directed upward. The drum unit14includes a Scorotron charger (not shown) disposed in confrontation with the lower part of the photosensitive drum16. The developing unit15is configured to rotatably support a developing roller (developing agent carrying member)17. The developing roller17is rotatably supported at the rear side in the upper portion of the developing unit15. The rear side of the developing roller17is exposed in the developing unit15in which toner of one of four colors is stored. The developing roller17is in contact with the front side of the photosensitive drum16.

In operation, the toner stored in the developing unit15is carried on the surface of the developing roller17in accordance with rotations of the developing roller17. On the other hand, the surface of the photosensitive drum16has been uniformed charged by the charger before reaching the position of the developing unit15. After being charged, the photosensitive drum16is exposed to laser beam (see dotted line inFIG. 1) emitted from the scanner unit8. The laser beam scans the surface of the photosensitive drum16at a high speed to form an electrostatic latent image corresponding to an image to be formed on a sheet of paper P.

In accordance with further rotations of the photosensitive drum16, the toner carried on the surface of the developing roller17is supplied to the electrostatic latent image formed on the surface of the photosensitive drum16. The electrostatic latent image is then visualized and a reversely developed toner image is carried on the surface of the photosensitive drum16.

The image transfer unit10includes a belt unit18and the secondary image transfer roller19. The belt unit18is disposed above the process unit9to confront the respective photosensitive drums16. The belt unit18includes a drive roller20, a follower roller21, the intermediate image transfer belt22, and four primary image transfer rollers23. The drive roller20and the follower roller21are spaced apart in the front-to-rear direction to confront each other. The intermediate image transfer belt22is circularly movably wound onto the two spaced-apart rollers20,21with taut. The intermediate image transfer belt22driven by the drive roller20has a lower part moving rearward and an upper part moving frontward. The photosensitive drums16are disposed to contact the lower part of the intermediate image transfer belt22.

The primary image transfer roller23is rotatably disposed above the corresponding photosensitive drum16to be in confrontation therewith the lower part of the intermediate image transfer belt22interposed therebetween. The belt unit18per se is configured to be rotatably movable about a fulcrum positioned at the rear end of the belt unit18. The belt unit18is movable in interlocking relation with the movements of the front cover5. Specifically, the belt unit18is in a transfer position (seeFIG. 1) when the front cover5is closed, in which the belt unit18is in contact with the photosensitive drums16, whereas the belt unit18is moved to a retracted position (seeFIG. 8) when the front cover5is opened, in which the belt unit18is separated from the photosensitive drums16.

The secondary image transfer roller19is rotatably disposed at the rear side of the belt unit18to confront the drive roller20of the belt unit18with the intermediate image transfer belt22inter posed therebetween.

The toner images held on the respective photosensitive drums16are sequentially transferred onto the lower part of the intermediate image transfer belt22moving rearward, thereby forming a color image on the intermediate image transfer belt22. The image transfer onto the intermediate image transfer belt22is referred to as a “primary image transfer”. The color image on the intermediate image transfer belt22is transferred onto a sheet of paper P fed from the sheet supplying section3when the color image passes past the secondary image transfer roller19. The image transfer by the secondary image transfer roller19is referred to as a “secondary image transfer” in contrast to the “primary image transfer”.

The color image thus transferred onto the sheet of paper P is thermally fixed by a fixing unit11. The fixing unit11includes a heat roller24and a pressure roller25. The sheet of paper P with the color image thermally fixed thereon is discharged onto a discharge tray26formed on the upper surface of the housing2.

As shown inFIGS. 2 and 3, the process unit9includes a plurality of process cartridges13, and a drawer frame12for mounting the process cartridges13thereon. As shown inFIG. 2, in this embodiment, mounted on the drawer frame12are four process cartridges including black process cartridge13K, yellow process cartridge13Y, magenta process cartridge13M and cyan process cartridge13C. It should be noted that the process cartridges are generally denoted by reference numeral13but a specific color process cartridge is denoted by a combination of reference numeral13and an alphabetical letter designating a color of toner. To facilitate the following description, it is assumed that the yellow process cartridge13Y is unused new one and the remaining three process cartridges are used ones but are still usable as the toner remains therein.

The process cartridge13is generally of a prism-shape and elongated in the left-to-right direction. Each process cartridge13includes the drum unit14and the developing unit15. The drum unit14has a pair of supporting plates31provided at the left and right sides thereof for rotatably supporting the photosensitive drum16. Beneath the photosensitive drum16, a frame (not shown) is bridged between the pair of supporting plates31for supporting the charger. Each supporting plate31is generally rectangular as viewed from right or left side. The supporting plate31is formed with drum supporting portion32, sleeve bearing36, developing unit supporting hole33, guide groove34, projected portion35and stop portion58(seeFIG. 5).

The drum supporting portion32formed in each of the pair of supporting plates31is a generally circular notched portion or a through-hole formed at the upper rear position thereof. The drum supporting portion32is formed for receiving the left and right ends of the photosensitive drum16. The sleeve bearing36is generally of a cylindrical shape projecting outward from the supporting plate31. The outer diameter of the sleeve bearing36is the same as the diameter of the drum supporting portion32. The sleeve bearing36and the drum supporting portion32in each of the pair of supporting plates31rotatably support the left or right end portion of the photosensitive drum16.

The developing unit supporting hole33is a circular through-hole formed at the central portion of the supporting plate31. The developing unit supporting hole33receives the supporting boss52(to be described later) of the developing unit15to be rotatable therein. The guide groove34is formed linearly to extend upward from the lower center of the supporting plate31. The guide groove34has a groove width in the front-to-rear direction capable of receiving a separation release rib62(to be described later) of the drawer frame12.

An engagement hole37is formed at a position slightly higher than the center of the guide groove34. The engagement hole37has an opening of a rectangular shape and penetrates the bottom wall42of the guide groove34. As shown in3A, the engagement hole37is provided for receiving the engaging projection55(to be described later) of the developing unit15when the drum unit14and the developing unit15are positionally separated (to be described later). In other words, the bottom wall42of the guide groove34functions as an engaging portion.

The projected portion35is a trapezoidal shape with the upper sider shorter than the lower side. Specifically, the front side of the projected portion35projects upward from the upper end of the supporting plate31further than the rear side of the projected portion35. The upper surface38in the rear portion of the projected portion35is slanted diagonally upward toward the front side. The upper surface38of the rear portion and the upper surface39of the front portion both defining the projected portion35are continuous and extend in the front-to-rear direction.

The stop portion58is in the form of a rectangular column extending in the left-to-right direction and disposed between the inner surfaces of the left and right side supporting plates31(seeFIG. 5). The left side supporting plate31is formed with a coupling view window41. The coupling view window41is formed in front of the drum supporting hole32and in the upper side of the guide groove34. The coupling view window41is a circular hole with a diameter same as that of a development coupling support hole48(to be described later). The coupling view window41and the development coupling support hole48are brought into coincidence with each other when the drum unit14and the developing unit15are in a contact position where the two are in contact with each other (to be described later) as shown inFIG. 3B.

As shown inFIG. 4, the developing unit15includes a development housing46made of a resin. The development housing46is an elongated box-shape extending in the left-to-right direction. As shown inFIG. 6, the development housing46is formed with a development opening47. The development housing46includes left and right side support arms49, left and right side engagement member accommodating grooves54, and an engagement member53functioning as a separation member.

As best shown inFIG. 6, the development opening47is formed in the upper rear portion of the development housing46and open to rearward. The developing roller17is rotatably supported inside the development opening47so that the rear portion of the developing roller17is exposed. Each support arm49is generally in a convex shape having a protruded portion protruding rearward as viewed from the side. The support arm49is provided with a support boss52. The support boss52is in the form of a round column extending outward from the support arm49. The outer diameter of the support boss52is approximately equal to or slightly smaller than the diameter of the developing unit supporting hole33.

The engagement member accommodating groove54is formed in the lower portion of each side wall of the development housing46. The groove54is formed in the outer surface of the side wall to be recessed inward and extends in the front-to-rear direction. The outer profile of the groove54is seen to be a rectangular shape. The groove54has a depth (rightward depth for the left side wall and leftward depth for the right side wall) for absorbing resilient deformation (deflection) of the engagement member53deformed inward when the drum unit14and the developing unit15are in a contact position.

The engagement member53is a rectangular plate-shaped member disposed within the engagement member accommodating groove54. The engagement member53extends rearward from the frontmost end of the groove54. The engagement member53is made of resin and formed integral with the development housing46. The engagement member53has a front end functioning as a fulcrum and a rear end or free end having resiliency to be deformable in the left-to-right direction. The direction in which the engagement member53extends is in coincidence with the left-to-right direction when the drum unit14and the developing unit15are separated. The engagement member53is formed with the engagement projection55.

The engagement projection55is formed in the rearmost end of the engagement member53and has an apex projecting outward in the left-to-right direction. The engagement projection55is a triangular shape when viewed from front to rear. The engagement projection55has an upwardly slanted lower surface56functioning as a second slanted surface.

The development coupling support hole48is formed in the left side wall of the development housing46. The support hole48is circular in rightward view and a development coupling51is rotatably engaged with the support hole48. The development coupling51is a female member in the form of a rounded column. A coupling male member (not shown) of the housing2is fitted to the left end of the female member51so that the male member and the female member are not rotatable relative to each other. The development coupling51is operatively coupled via gear trains (not shown) to the developing roller17and other members to be rotatable.

The developing unit15is rotatably supported between the two supporting plates31of the drum unit14. To support the developing unit15, the support bosses52are inserted into the developing unit supporting holes33formed in the left and right supporting plates31of the drum unit14.

As shown inFIG. 5, a compression spring57functioning as an urging member is disposed in the lower portion of the developing unit15. The compression spring57has a front end secured to the rear surface in the lower part of the developing unit15and a rear end secured to the stop portion58of the drum unit14. The compression spring57urges the developing unit15to rotate counterclockwise as viewed from the left side, so that the developing roller17is normally positioned closely to the photosensitive drum16. At the time of shipment, the developing unit15is fixed between the left and right supporting plates31of the drum unit14. Specifically, as shown inFIG. 3A, the engaging projections55are inserted into the engagement holes37of the drum unit14, thereby holding the developing roller17in a position spaced apart from the photosensitive drum16at the front lower position thereof against the expansion force of the compression spring57. That is, the drum unit14and the developing unit15are in a separated position as shown inFIG. 4B.

At this time, the front upper end portion of the development housing46projects frontward from the front end portion of the drum unit14. Also, the front lower end portion of the development housing46projects downward from the lower end portion of the drum unit14. When the engagement projection55of the developing unit15is compressed inward, the rear end portion of the engagement member53is resiliently deformed inward in the left-to-right direction. As a result, the engagement projection is retracted inward from the engagement hole37of the drum unit14, thereby disengaging the engagement projection55from the engagement hold37of the drum unit14. Then, by virtue of the expansion force of the compression spring57, the developing unit15is rotated counterclockwise as view from the left side from the separated position. This brings the developing roller17into pressure contact with the photosensitive drum16and thus the drum unit14and the developing unit15are disposed in a contact position as shown inFIG. 5. At this time, the outer end portion of the engagement projection55is brought into abutment with the inner surface of the supporting plate31of the drum unit14, thereby remaining the rear end portion of the engagement member52in an inwardly deformed condition. In other words, the supporting plates31of the drum unit14functions as a holding member.

When the drum unit14and the developing unit15are in the contact position, the front upper end portion of the development housing46is in flush with the front end portion of the drum unit14, and the front lower end portion of the development housing46is in flush with the lower end portion of the drum unit14.

As shown inFIG. 6, the drawer frame12is generally rectangular in plan view and is defined by a front wall, a rear wall, and a pair of side walls60disposed in spaced apart and in confronting relation with each other. Each side wall60is formed with four guide ribs61and four separation release ribs62. Each side wall60is further formed with four drum supporting grooves63. The guide ribs61in each side wall60are aligned in the front-to-rear direction with a predetermined interval between two adjacent guide ribs61. The predetermined interval is equal to or slightly longer than the front-to-rear length of the supporting plate31of the process cartridge13. The frontmost guide rib61is provided to be continuous to the rear side of the front wall of the drawer frame12. The rearmost guide rib61is provided at a position in front of the rear wall of the drawer frame12with an interval equal to or slightly longer than the front-to-rear length of the supporting plate31of the process cartridge13.

The guide ribs61are provided corresponding to the respective ones of the process cartridges13individually. The guide ribs61in each side wall60project inward and extend in vertical direction over the entire vertical width of the side wall60.

The separation release ribs62are provided corresponding to the respective ones of the process cartridges13individually. Each separation release rib62projects inward and extends in vertical direction from the lower edge portion to the center of the side wall60. The separation release ribs62are provided one by one between the rearmost guide rib61and the rear wall of the drawer frame12and between two adjacent guide ribs61.

Each separation release rib62is formed with a position restricting surface (first slanted surface)65. The upper slanted surface of the separation release rib62serves as the position restricting surface65. The upper surface65of the separation release rib62is slanted to decrease its height toward the inner side.

The drum supporting grooves63are provided one by one at the rear side of the separation release ribs62between the rearmost guide rib61and the rear wall of the drawer frame12and between two adjacent guide ribs61. The drum supporting groove63is of a concave shape as viewed from the left or right side and formed at the upper end face of the side wall60. Specifically, the drum supporting groove63has inner tapered surfaces. The front-to-rear distance between the opposing inner tapered surfaces decreases as the groove63goes deeper level. The front-to-rear distance of the groove63at the upper end face is longer than the outer diameter of the sleeve bearing36.

Four coupling view windows64are formed in the left side wall60. The coupling windows64are formed one by one in the front side of the drum supporting grooves63and are circular having a diameter as large as that of the coupling view window41of the process cartridge13. The coupling view window64is brought into coincidence with the coupling view window41of the process cartridge13when the process cartridge13is disposed in the second position (to be described later), as shown inFIG. 10.

At the time of shipping the color printer1, the drawer frame12is separated from the housing2. The process cartridges13are supported on the drawer frame12in such a state that the drum unit14and its associated developing unit15are separated. To support the process cartridges13on the drawer frame12, the user has to grasp the process cartridge13while maintaining the rear side of the photosensitive drum14at the upper position, and then place the sleeve bearing36of the process cartridge13above the drum supporting groove63so that the associated guide groove34is positioned above the separation release rib62of the drawer frame12.

Next, the process cartridge13is mounted on the drawer frame12from the upper side thereof. Then, the guide groove34of the drum unit14is brought into engagement with the separation release rib62. As shown inFIG. 7, the lower surface56of the engaging projection55of the developing unit15is brought into abutment with the position restricting surface65of the separation release rib62of the drawer frame12from the upper side. That is, the guide groove34functions to guide the abutment of the separation release rib62and the engagement projection55.

Due to the structure described above, the process cartridge13is prevented from being further inserted into the drawer frame12, so that the process cartridge13is forced to be in the first position. This description applies to the yellow process cartridge12Y shown inFIG. 8. That is, the upper portion of the separation release rib62functions as a position restricting portion.

At this time, the engagement projection55of the developing unit15is engaged with the engagement hole37, thereby bringing the drum unit14and the developing unit15to be in a separated condition. As in the yellow process cartridge13Y shown inFIG. 2, the sleeve bearing36of the process cartridge13is in confrontation with the lower wall of the drum supporting member53with an interval therebetween.

The engagement member53of the developing unit15is so rigid that it does not deform by the external force which may be applied thereto at the time of shipping.

As shown inFIG. 8, the housing2is provided with a interfering member71. The interfering member71is generally semi-circular shaped having a semicircular portion at the lower portion. The interfering member71is provided at the front end of the housing2. Specifically, the interfering member41is disposed in the upper side of the cartridge mounting/removal path where the interfering member41is in abutment with the projected portion35of the process cartridge13disposed in the first position whereas the interfering member41is not in abutment with the process cartridge13disposed in the second position (to be described later with reference toFIG. 10). A separation release mechanism is configured by the interfering member71together with the separation release rib62.

Next, mounting of the process cartridge13will be described. The following description pertains to a replacement procedure of the yellow process cartridge13Y.

In order to place the yellow process cartridge13Y in the housing2, it is firstly necessary to open the front cover5as shown inFIG. 8. Then the process unit9is pulled out of the housing2and the used yellow process cartridge13Y is removed upward from the drawer frame12. A new yellow process cartridge13Y is mounted on the drawer frame12to be stopped in first position, whereupon the drawer frame12is moved to the mount position.

As shown inFIG. 9, the rear surface38of the projected portion35of the yellow process cartridge13Y is brought into abutment with the interfering member71on the way to the mount position from the pull-out position. When the user further inserts the drawer frame12into the housing2, the yellow process cartridge13Y is urged downward by the interfering member71as the slanted rear surface of the projected portion35slides along the lower part of the circular section of the interfering member71. The yellow process cartridge13Y is moved downward and the lower surface56of the engaging projection of the developing unit15is inwardly urged by the position restricting surface65of the separation release rib62. This causes the rear end of the engagement member53to resiliently deform inward in the left-to-right direction, so that the engagement projection55is disengaged from the engagement hole37of the drum unit14. As a result, the developing unit15is rotated counterclockwise as viewed from the left side from the separated position by virtue of the expansion force of the compression spring57.

The developing roller17is then brought into pressure contact with the photosensitive drum16, thereby placing the drum unit14and the developing unit15in the contact state. In this state, the yellow process cartridge13Y is available for forming images (seeFIG. 5). At this time, when the engagement projection55is retracted inward from the engagement hole37of the drum unit14, the lower surface56of the engagement projection55of the developing unit15is no longer in abutment with the position restricting surface65of the separation release rib62formed in the drawer frame12.

Then, the yellow process cartridge13Y is no longer restricted to the first position. As shown inFIG. 10, the yellow process cartridge13Y is moved downward and the sleeve bearing36of the yellow process cartridge13Y is brought into engagement with the drum support groove63. The yellow process cartridge13Y is thus held in the second position. (Refer to the process cartridges other than the yellow process cartridge13Y shown inFIG. 2.) To summarize, the replaced process cartridges13are firstly placed in the first position before the drawer frame12is in the pull-out position and then placed in the second position upon completion of the cartridge mounting procedure and during movements of the drawer frame12toward the mount position.

Thereafter, the drawer frame12is accommodated in the mount position and the front cover5is closed. Then, the belt unit18is placed in the transfer position and the upper part of the belt unit18is brought into contact with the photosensitive drums16. This completes mounting the yellow process cartridge13Y on the housing2.

A new, unused printer1is in such a condition that the process unit9is separated from the housing2or the process cartridges13are placed in the first position on the drawer frame12. In this case, the process unit9is accommodated into the housing2while holding the process cartridges13in the first position. In accordance with the movements of the process unit9toward the mount position, each process cartridge13is sequentially brought into abutment with the interfering member71and moved from the first position to the second position. In this way, in all the process cartridges13, the drum unit14and the developing unit15are brought to a contact state.

The printer1is operable either in a monochromatic printing mode for printing a monochromatic (black and white) images or a color printing mode for printing a full color images. In order to switch the color printing mode to the monochromatic printing mode, the photosensitive drums16of the color (yellow, magenta and cyan) process cartridges13and the associated developing rollers17are separated by a distance shorter than the distance between the photosensitive drum16and the developing roller17which are disposed in the above-described separated condition. That is, the developing unit15is rotated less than the rotating amount of the developing unit15in the separated condition. The engagement projection55is not engaged with the engagement hole37again at the time of switching between the monochromatic print mode and the color printing mode but is held under the condition in which the engagement projection55is disengaged from the engagement hole37.

Next, operational advantages of the embodiment will be described.

(1) As shown inFIG. 3, the printer1uses a process cartridge13in which the engagement member53is provided for holding the drum unit14and the developing unit15in the separated position.

As shown inFIGS. 9 and 10, the drawer frame12movably supports the process cartridge13to be movable between the first position where image formation with toner (developer) is disabled and a second position where image formation with toner is enabled.

The separation release mechanism (interfering member71and the separation release rib62) not only moves the process cartridge13from the first position to the second position attendant to the movement of the drawer frame12from the pull-out position to the mount position but also releases holding the drum unit14and the developing unit15in the separated position.

As such, at the time of transportation or storage in the course of shipping the printer1, insofar as the drum unit14and the developing unit15are held in the separated position, deformation of the developing roller17may not occur.

Under a condition where the process cartridge13is placed in the first position, the drawer frame12is inserted into the housing2in order to place the printer2in a print ready condition. The movements of the drawer frame12from the pull-out position to the mount position can move the process cartridge13from the first position to the second position. Also, the drum unit14and the developing unit15are no longer held in the separated position.

The process cartridge13can be set to the second position where images can be formed and also the developing roller17can be brought into contact with the associated photosensitive drum16in linking relation with the insertion of the drawer frame12into the housing2.

(2) In the printer1, the separation release mechanism is provided with the interfering member71and the separation release rib62. When the drawer frame12is moved from the pull-out position to the mount position, the process cartridge13restricted to the first position by the separation release rib62can be moved to the second position by virtue of the interfering member71provided at the side of the housing2. At this time, holding the drum unit14and the developing unit15in the separated position by the engagement member53can be released by the separation release rib62. As such, the drum unit14and the developing unit15are no longer restricted to be held in the separated position in interlocking relation with the insertion of the drawer frame12into the housing2.

As shown inFIGS. 9 and 10, the printer1has the drawer frame12on which the process cartridges13are detachably mounted. The process cartridge13is vertically moved for mounting on the drawer frame12along a direction from the first position of the process cartridge13to the second position thereof. Thus, easy mounting of the process cartridges13onto the drawer frame12can be achieved.

As shown inFIG. 3, the engagement hole37for engaging the engagement member53therewith is formed in the bottom wall42of the guide groove34formed in the drum unit14. By such a simple structure, the developing roller17can remain separated from the photosensitive drum16.

As shown inFIG. 7, the separation release rib62projects inward in the left-to-right direction from the side wall60of the drawer frame12and extends vertically. Further, the engagement member53is provided in the outside end portion in the left-to-right direction of the process cartridge13. With such a simple structure, the separation release rib62can be brought into abutment with the engagement member53.

As shown inFIGS. 6 and 7, the position restricting surface65is formed in the upper end portion of the separation release rib62. The position restricting surface65restricts the process cartridge13to be in the first position by the abutment with the engagement member53. As such, with the use of the upper end portion of the separation release rib62, the process cartridge13can be restricted to the first position. Accordingly, without increasing the number of parts, yet with a simple structure, restricting the process cartridge13to the first position and also disengagement of the engagement member53from the engagement hole37can be accomplished.

As shown inFIG. 7, the position restricting surface65which is a slanted surface facing upward is formed in the upper end portion of the separation release rib62, and the lower surface56of the engagement projection65formed in the engagement member53is brought into abutment with the position restricting surface65. As such, when the process cartridge13is moved from the first position to the second position, the engagement projection55can be smoothly urged inward due to the slanted position restricting surface65. In other words, moving the process cartridge13from the first position to the second position enables smooth disengagement of the engagement member53from the engagement hole37.

As shown inFIG. 3, the engagement hole37is formed within the vertically elongated guide groove34. Further, the engagement projection55is engaged with the engagement hole37within the guide groove34. The separation release rib62is guided relative to the engagement projection55while being engaged with the guide groove34. Accordingly, by utilizing the guide groove34, the separation release rib62can be guided relative to the engagement projection55when the process cartridge13is placed in the first position. Additional guide member for guiding the separation release rib62relative to the engagement projection64is not required. Abutment of the separation release rib62with the engagement projection55can be ensured with such a simple structure.

The engagement member53is made of a resilient material. Against the resiliency of the engagement member53, the separation release rib62resiliently deforms the engagement member53, thereby causing the engagement projection55to move inward in the left-to-right direction. Accordingly, the resiliency of the engagement member53allows the engagement member52to be kept engaged with the engagement hole37, and resilient deformation of the engagement member53easily disengages the engagement member55from the engagement hole37.

As shown inFIG. 5, the process cartridge13used in the printer1is provided with the compression spring57for urging the developing unit15against the drum unit14so as to bring the developing roller17into contact with the photosensitive drum16. When the engagement projection55is disengaged from the engagement hole37, the developing roller17can be brought into contact with the photosensitive drum16due to the expansion force of the compression spring57.

As shown inFIG. 3B, the supporting plate31of the process cartridge13holds the engagement member53in a position to no longer keep the drum unit14and the developing unit15in the separation position once the process cartridge13is moved to the second position. Accordingly, once the process cartridge13is moved to the second position, the developing roller17can be constantly held in a state to contact the photosensitive drum16.

As shown inFIG. 11, the process cartridges13are arranged in the front-to-rear direction with spacing between the adjacent two. The developing roller17can be brought into contact with the photosensitive drum16when the process cartridges13are mounted on the housing2of the drawer frame12and the latter is moved to the image formable second position.

As shown inFIGS. 9 and 10, the drawer frame12of the printer1is movable in the front-to-rear direction between the mount position and the pull-out position. Provision of a single interfering member71in between the two positions, the process cartridge13disposed in the first position can be brought into abutment with the interfering member71bwithout fail. In this way, all of the process cartridges13can be accurately shifted to the second position with such a simple structure. In addition, the developing roller17can be brought into contact with the photosensitive drum16.

While referring toFIG. 11, a first modification of the above-described embodiment will be described. In the following description relating to the first modification, the same reference numerals used in the description of the embodiment will also be used in the description of the first modification to denote the same components, and the duplicated description thereof will be omitted.

In the above-described embodiment, the engagement member53is formed within the engagement member accommodating groove54. The engagement member53extends continuously from the outer end of the front wall defining the engagement member accommodating groove54to the rear side. Also, the engagement member53is integrally formed with the development housing46. However, in accordance with the first modification, as shown inFIG. 11, the engagement member76is provided independently of the development housing46and disposed within the engagement member accommodating groove54to be rotatable.

More specifically, the engagement member76is generally in the form of a plate-shape. The engagement member76is formed with a pair of rotational shafts77at the center thereof in the front-to-rear direction. The rotational shafts77are generally in the form of a rounded column one extending upward and the other extending downward from the respective outer edges of the engagement member76. The center axial lines of the two rotational shafts77are in alignment with each other.

The engagement member76is rotated clockwise in the plan view in accordance with the pushing action of the engagement protrusion55. The engagement protrusion55is pushed inward in the left-to-right direction by the separation release rib62. The engagement protrusion55is accommodated in the engagement accommodating groove54due to the clockwise rotations of the engagement member76, and disengaged from the engagement hole37. The engagement member accommodating groove54has a front wall to which the stop78is provided. The stop78functions as the holding member.

The stop78is generally in the form of a rectangular shape as viewed from the side that projects from the vertical center of the front wall of the engagement member accommodating groove54toward the rear side. As shown inFIG. 11A, when the engagement projection55of the engagement member76is in engagement with the engagement hole37, the stop78abuts the front end portion of the engagement member76from the outer side in the left-to-right direction, resulting in restricting the clockwise rotation of the engagement member76. When the engagement projection55is disengaged from the engagement hole37, the stop78is brought into abutment with the front end portion of the engagement member76from the inner side in the left-to-rear direction, restricting the counterclockwise rotation of the engagement member76. At the time of shipping the printer1, the stop78holds the front end portion of the engagement member76so as not to rotate.

Operational advantages as obtained in the above-described embodiment can also be obtained in the first modification.

While referring toFIG. 12, a second modification will be described. In the following description, the same reference numerals used in the description of the embodiment and/or the first modification will also be used in the description of the second modification to denote the same or corresponding components, and the duplicated description thereof will be omitted.

In the above-described embodiment, the engagement member53is provided in the developing unit15, and the guide groove34with the engagement hole37is formed in the drum unit14. Insertion of the engagement member53into the engagement hole37holds the developing unit15and the drum unit14to be fixedly disposed.

As shown inFIG. 12, in accordance with the second modification, a first holding member81functioning as the separation member is provided in the drum unit14, and a second holding member82functioning as a holding portion is formed in the developing unit15.

More specifically, the supporting plate31of the drum unit14is formed with a cut-away portion84. The cut-way portion84is generally rectangular as viewed from the side and is formed in the lower end and front half of the supporting plate31. The cut-away portion84has a rear wall from which an elongated plate-like member functioning as the first holding member81extends frontward. The first holding member81is a resiliently deformable material, such as resin, and is formed integrally with the supporting plate31. The first holding member81has a front tip end formed with an engagement projection55similar to the corresponding component in the above-described embodiment.

The development housing46of the developing unit15is provided with a second holding member82and the guide wall83. The second holding member82is formed in the lower portion of the development housing46and is generally an L-shape extending outward in the left-to-right direction from the outer side surface of the development housing46and bent downward.

The guide wall83is provided in front of the second holding member82. The guide wall83and the engaging projection55are spaced apart by a distance equal to or slightly longer than the front-to-rear length of the engaging projection55. The guide wall83is generally rectangular as viewed from the side and protrudes outward in the left-to-right direction from the development housing46.

The engaging projection55of the first holding member81is brought into engagement from the inner side into a gap between the second holding member82and the guide wall83, thereby maintaining the drum unit14and the developing unit15in a separated condition. Further, the space between the second holding member82and the guide wall83serves as a groove for bringing the separation release rib62and the engaging projection55into abutment with each other. The first holding member82has a front end portion that is resiliently deformed inward in the left-to-right direction by the engaging protrusion55urged inward in the left-to-right direction by the separation release rib62. The resilient deformation of the first holding member82causes the engaging protrusion55to be unrestricted by the gap between the second holding member82and the guide wall83. As a result, the drum unit14and the developing unit15are no longer restricted to the separated condition.

Advantageous as obtained in the above-described embodiment are also obtainable in the second modification.