Image forming apparatus having supporting member for supporting cartridges

An image forming apparatus includes: a main casing; a plurality of cartridges each extending in a first direction substantially perpendicular to a vertical direction; and a supporting member configured to detachably support the plurality of cartridges such that the cartridges are arrayed in a second direction substantially perpendicular to the vertical direction and the first direction. The supporting member is movable between an inner position disposed within the main casing and an outer position disposed outside of the main casing. The supporting member includes: a first side plate; a second side plate positioned opposite to and spaced away from the first side plate in the first direction; and a prescribed number of beam plate connecting between the first side plate and the second side plate, the prescribed number being in a range of from one to not more than a number of the cartridges.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2013-072076 filed Mar. 29, 2013. The entire content of the priority application is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an electro-photographic image forming apparatus.

BACKGROUND

A known tandem-type color printer includes a main body and a plurality of cartridges detachably mountable in the main body.

One of such conventional color printers includes a main body and a cartridge tray configured to be held in the main body so as to be slidable relative to the main body. In this color printer, the cartridge tray supports therein a plurality of cartridges juxtaposed to one another (see Japanese Patent Application Publication No. 2008-165025).

SUMMARY

It is an object of the present invention to provide an improved image forming apparatus.

In order to attain the above and other objects, there is provided an image forming apparatus including: a main casing; a plurality of cartridges; and a supporting member. Each of the plurality of cartridges extends in a first direction substantially perpendicular to a vertical direction and accommodates developer. The supporting member is configured to detachably support the plurality of cartridges such that the cartridges are arrayed in a second direction substantially perpendicular to the vertical direction and the first direction, the supporting member being movable between an inner position disposed within the main casing and an outer position disposed outside of the main casing. The supporting member includes a first side plate, a second side plate, and a prescribed number of beam plate. The second side plate is positioned opposite the first side plate to be spaced away therefrom in the first direction. The prescribed number of beam plate connects between the first side plate and the second side plate, the prescribed number being in a range of from one to not more than a number of the cartridges.

According to another aspect of the present invention, there is provided an image forming apparatus including a main casing, a drawer and a plurality of cartridges. The drawer is movable in a first direction between an inner position disposed within the main casing and an outer position disposed outside of the main casing. Each of the plurality of cartridges accommodates developer therein and is configured to be detachable and attachable relative to the drawer. The drawer includes a first side wall, a second side wall and a prescribed number of beam plate. The second side wall is disposed at a position opposite to the first side wall with respect to the plurality of cartridges in a second direction perpendicular to the first direction. The prescribed number of beam plate connects between the first side plate and the second side plate, the prescribed number being in a range of from one to not more than a number of the cartridges.

DETAILED DESCRIPTION

1. General Structure of the Printer

A printer1is a horizontal direct tandem-type color laser printer, as shown inFIG. 1. The printer1is an example of an image forming apparatus according to a first embodiment of the present invention.

First, a general structure of the printer1will be described with reference toFIG. 1.

Throughout the specification, the terms “above”, “below”, “right”, “left”, “front”, “rear” and the like will be used assuming that the printer1is resting on a level surface. More specifically, inFIG. 1, a right side, a left side, a near side and a far side will be referred to as a front side, a rear side, a left side and a right side of the printer1, respectively.

(1) Main Casing

The main casing2has a substantially rectangular box shape in a side view. The main casing2has a front wall formed with a main body opening6, and a front cover7. The front cover7is configured to be pivotally movable about a lower end portion thereof between a closing position closing the main body opening6(show by a solid line inFIG. 1) and an opening position opening the main body opening6(shown by a dotted line inFIG. 1). The main casing2houses therein a sheet supply section3and an image forming section4.

(2) Sheet Supply Section

The sheet supply section3has a sheet cassette8, a sheet supply guide9and a pair of registration rollers10. The sheet cassette8serves to accommodate sheets of paper P therein. The sheet cassette8is detachably attached to a bottom portion of the main casing2.

The sheets P stacked in the sheet cassette8are fed one by one, and directed upward and rearward toward between the pair of registration rollers10while being guided along a U-shaped path by the sheet guide9, and then conveyed at a prescribed timing toward between a photosensitive drum18(described later) and a conveying belt25(described later) of the image forming section4.

(3) Image Forming Section

The image forming section4includes a scanner unit11, a drawer unit12, a transfer unit13, and a fixing unit14.

(3-1) Scanner Unit

The scanner unit11is disposed at an upper portion of the main casing2. The scanner unit11emits a laser beam to each of a plurality of photosensitive drums18(described later) based on image data to expose the corresponding photosensitive drum18to light.

(3-2) Drawer Unit

The drawer unit12is disposed at a position generally center of the main casing2in an up-down direction and below the scanner unit11.

The drawer unit12includes a drawer frame40and four process cartridges17corresponding to respective four colors used in the printer1. The four process cartridges17are attachable to and detachable from the drawer frame40.

The drawer unit12is configured to move in a front-rear direction between an inner position (denoted by a solid line) at which the drawer unit12is positioned inside the main casing2and an outer position (denoted by an imaginary line) at which the drawer unit12is positioned outside the main casing2.

The four process cartridges17are arranged spaced apart from one another in the front-rear direction in the drawer frame40. The process cartridges17include a black process cartridge17K, a yellow process cartridge17Y, a magenta process cartridge17M, and a cyan process cartridge17C arranged in the drawer frame40in the mentioned order from the front to the rear.

Each of the four process cartridges17has the photosensitive drum18, a charging roller19, a developing roller20, a supply roller21, and a thickness regulation blade22.

The photosensitive drum18has a substantially cylindrical shape extending in a left-right direction. The photosensitive drum18is rotatably supported by a lower end portion of the process cartridge17. A lower end portion of the photosensitive drum18is exposed downward from the process cartridge17.

The charging roller19has a substantially columnar shape extending in the left-right direction. The charging roller19is rotatably supported in the process cartridge17to be in contact with an upper rear portion of the photosensitive drum18.

The developing roller20has a substantially columnar shape extending in the left-right direction. The developing roller20is rotatably supported in the process cartridge17to be in contact with an upper portion of the photosensitive drum18.

The supply roller21has a substantially columnar shape extending in the left-right direction. The supply roller21is rotatably supported in the process cartridge17to be in contact with an upper portion of the developing roller20.

The thickness regulation blade22is rotatably supported in the process cartridge17to be in contact with a rear portion of the developing roller20.

Each process cartridge17houses toner of one of respective colors.

The toner in the process cartridge17is supplied to the supply roller21, then to the developing roller20. At this time, the toner is tribo-charged with a positive polarity between the supply roller21and developing roller20.

Then, as the developing roller20rotates, the toner on the developing roller20is regulated by the thickness regulation blade22and carried as a thin toner layer of a uniform thickness on a surface of the developing roller20.

In the meantime, a surface of the photosensitive drum18is uniformly and positively charged by the charging roller19as the photosensitive drum18rotates. Then, the scanner unit11emits a laser beam to the charged surface of the photosensitive drum18to expose the surface of the photosensitive drum18to light. As a result, an electrostatic latent image corresponding to an image to be formed on the sheet P is formed on the surface of the photosensitive drum18.

As the photosensitive drum18further rotates, the toner carried on the surface of the developing roller20and having a positive polarity is supplied to the electrostatic latent image formed on the surface of the photosensitive drum18. In this way, a toner image is formed on the surface of the photosensitive drum18through a reversal phenomenon.

(3-3) Transfer Unit

In the main casing2, the transfer unit13is disposed above the sheet supply section3but below the drawer unit12within the main casing2. The transfer unit13extends in the front-rear direction.

The transfer unit13includes a drive roller23, a driven roller24, the conveying belt25, and four transfer rollers26.

The drive roller23and driven roller24are arranged to be spaced apart from each other in the front-rear direction. The conveying belt25is mounted on and around the drive roller23and driven roller24in a tout state. Each of the four transfer rollers26is disposed to correspond to the corresponding one of the four photosensitive drums18such that an upper portion of the conveying belt25is interposed between each of the pairs of the transfer roller26and the photosensitive drum18. Each pair of the transfer roller26and the photosensitive drum18defines a transfer position therebetween on the conveying belt25.

The sheet P supplied from the sheet supply section3is conveyed by the conveying belt25conveys from the front side to rear side to sequentially passes through the four transfer positions. During passage of the sheet P through the transfer positions, the toner images of the respective colors carried on the respective photosensitive drums18are sequentially superimposed onto the sheet P to form a color image thereon.

(3-4) Fixing Unit

The fixing unit14is disposed rearward of the transfer unit13. The fixing unit14includes a heating roller29and a pressure roller30. The pressure roller30is disposed adjacent to the heating roller29to be positioned at a lower rear side of the heating roller29.

As the sheet P passes between the heating roller29and pressure roller30, the toner image transferred onto the sheet P is thermally fixed thereon due to application of heat and pressure by the heating roller29and pressure roller30.

(4) Sheet Discharge Section

The sheet discharge section5is disposed above the fixing unit14. The sheet discharge section5includes a discharge guide29, a discharge port30, a pair of discharge rollers31, and a discharge tray32.

The sheet P on which the toner image has been thermally fixed in the fixing unit14is fed upward and frontward while making a U-turn with a guide by the discharge guide29. The sheet P then passes between the pair of discharge rollers31, and is finally discharged onto the discharge tray32through the discharge port30.

2. Drawer Unit of the First Embodiment

The drawer unit12of the first embodiment includes the drawer frame40and the four process cartridges17detachably accommodated in the drawer frame40.

The drawer frame40is configured to support the four process cartridges17arranged in the front-rear direction. Further, the drawer frame40is configured to be slidable in the front-rear direction relative to the main casing2. Specifically, the drawer frame40supporting the process cartridges17is capable of moving between the inner position at which the drawer unit12is attached to the main casing2and the outer position at which the drawer unit12is detached from the main casing2as described above.

As illustrated inFIG. 2, the drawer frame40includes a left side plate41and a right side plate42arranged to be spaced away from each other in the left-right direction, and three beam plates43connecting between the left side plate41and the right side plate42. The left side plate41and right side plate42extend in the front-rear direction.

The left side plate41is substantially rectangular flat plate shaped in a side view. Although not illustrated, the left side plate41has a bottom end portion that is bent rightward. The left side plate41thus has a substantially L-like shape in a front view. Further, the left side plate41has a right side surface from which two left protruding plates71protrude rightward up to a position midway between the left side plate41and right side plate42in the left-right direction. Each left protruding plate71has substantially a rectangular flat plate in a front view. Each left protruding plate71has a right end portion (protruding end) that is positioned leftward of a center between the left side plate41and right side plate42in the left-right direction. The left protruding plates71are configured of a front-left intermediate protruding plate71aand a rear-left intermediate protruding plate71b.

The front-left intermediate protruding plate71aprotrudes rightward from the right side surface of the left side plate41and is positioned at an intermediate position between the front end portion and center portion of the left side plate41in the front-rear direction (front intermediate position of the left side plate41).

The rear-left intermediate protruding plate71bprotrudes rightward from the right side surface of the left side plate41and is positioned at an intermediate position between the rear end portion and center portion of the left side plate41in the front-rear direction (rear intermediate position of the left side plate41).

The right side plate42is substantially a rectangular flat plate in a side view. Although not illustrated, the right side plate42has a bottom end portion that is bent leftward. The right side plate42thus has a substantially L-like shape in a front view. The right side plate42has a left side surface from which two right protruding plates72protrude leftward up to a position midway between the left side plate41and right side plate42in the left-right direction. Each right protruding plate72has substantially a rectangular flat plate in a front view. Each right protruding plate72has a left end portion (protruding end) that is positioned rightward of the center between the left side plate41and right side plate42in the left-right direction. The right protruding plate72are configured of a front-right intermediate protruding plate72aand a rear-right intermediate protruding plate72b.

The front-right intermediate protruding plate72aprotrudes leftward from the left side surface of the right side plate42and is positioned at an intermediate position between the front end portion and center portion of the right side plate42in the front-rear direction (front intermediate position of the right side plate42).

The rear-right intermediate protruding plate72bprotrudes leftward from the left side surface of the right side plate42and is positioned at an intermediate position between the rear end portion and center portion of the right side plate42in the front-rear direction (the rear intermediate position of the right side plate42).

The front-left intermediate protruding plate71aand front-right intermediate protruding plate72aare aligned with each other with respect to the left-right direction. Similarly, the rear-left intermediate protruding plate71band rear-right intermediate protruding plate72bare aligned with each other with respect to the left-right direction.

The left side plate41and right side plate42are formed of the same resin material (e.g., ABS) and have the same linear expansion coefficient as each other (e.g., 80×10−6/° C.).

The three beam plates43include a front beam43a, a rear beam43b, and a center beam43c. The beam plates43are formed of the same resin material and have the same linear expansion coefficient as one another. Further, the beam plates43are formed of the same resin material as those of the left side plate41and right side plate42and have the same linear expansion coefficient as those of the left side plate41and right side plate42.

The front beam43ais a flat plate having a substantially rectangular shape extending in the left-right direction in a front view. The front beam43aconnects the front end portion of the left side plate41and front end portion of the right side plate42. The front beam43ahas a front surface and a gripping part46protrudes frontward from the front surface at a center thereof in the left-right direction.

The rear beam43bhas substantially a rectangular shape in a front view and extends in the left-right direction. The rear beam43bhas a thickness larger than that of the front beam43ain the front-rear direction. The rear beam43bconnects the rear end portion of the left side plate41and rear end portion of the right side plate42.

The center beam43cis a flat plate having a substantially rectangular shape extending in the left-right direction in a front view. The center beam43cconnects the center portion of the left side plate41and center portion of the right side plate42and is positioned at a center between the front beam43aand rear beam43bin the front-rear direction.

The left side plate41, right side plate42, three beam plates43, left protruding plates71, and right protruding plates72define four cartridge housing spaces75.

Specifically, the front beam43a, front-left and front-right intermediate protruding plates71aand72a, and left and right side plates41and42between the front beam43aand front-left and front-right intermediate protruding plates71aand72adefine a first cartridge housing space75aextending in the left-right direction. The first cartridge housing space75ais located frontmost in the front-rear direction among the four cartridge housing spaces75.

The center beam43c, front-left and front-right intermediate protruding plates71aand72a, and left and right side plates41and42between the center beam43cand front-left and front-right intermediate protruding plates71aand72adefine a second cartridge housing space75bextending in the left-right direction. The second cartridge housing space75bis positioned to be the second from the front in the front-rear direction among the four cartridge housing spaces75.

The center beam43c, rear-left and rear-right intermediate protruding plates71band72b, and left and right side plates41and42between the center beam43cand rear-left and rear-right intermediate protruding plates71band72bdefine a third cartridge housing space75cextending in the left-right direction. The third cartridge housing space75cis positioned to be the second from the rear in the front-rear direction among the four cartridge housing spaces75.

The rear beam43b, rear-left and rear-right intermediate protruding plates71band72b, and left and right side plates41and42between the center beam43cand rear-left and rear-right intermediate protruding plates71band72bdefine a fourth cartridge housing space75dextending in the left-right direction. The fourth cartridge housing space75dis positioned rearmost in the front-rear direction among the four cartridge housing spaces75.

(2) Process Cartridge

Each process cartridge17includes a cartridge frame60.

As illustrated inFIG. 1, the cartridge frame60has a substantially box-like shape extending in the left-right direction and having a lower end portion that is open downward. The cartridge frame60supports the photosensitive drum18, charging roller19, developing roller20, supply roller21, and thickness regulation blade22.

The cartridge frame60has a front side surface61and a rear side surface62both extending in the left-right direction. The front side surface61and the rear side surface62constitute a front end and a rear end of the cartridge frame60respectively.

When the process cartridges17are respectively accommodated in the corresponding cartridge housing spaces75, the lower end portions of the left and right side plates41and42(the lower ends protruding inward in the left-right direction) support the cartridge frames60. As a result, the process cartridges17are supported in the drawer frame40.

The black process cartridge17K, yellow process cartridge17Y, magenta process cartridge17M and cyan process cartridge17C are respectively housed in the first cartridge housing space75a, second cartridge housing space75b, third cartridge housing space75cand fourth cartridge housing space75d. The black process cartridge17K has a cartridge frame60awith a front side surface61aand a rear side surface62a. The yellow process cartridge17Y has a cartridge frame60bwith a front side surface61band a rear side surface62b. The magenta process cartridge17M has a cartridge frame60cwith a front side surface61cand a rear side surface62c. The cyan process cartridge17C has a cartridge frame60dwith a front side surface61dand a rear side surface62d.

When the black process cartridge17K is housed in the first cartridge housing space75a, the front beam43ais positioned frontward of the front side surface61aof the cartridge frame60aof the black process cartridge17K to be spaced away therefrom in the front-rear direction. The front-left intermediate protruding plate71aand front-right intermediate protruding plate72aare positioned rearward of the rear side surface62aof the cartridge frame60aso as to be spaced apart therefrom in the front-rear direction.

Incidentally, when the black process cartridge17K is attached to and detached from the first cartridge housing space75a, the rear side surface62aof the black process cartridge17K is guided by the front-left intermediate protruding plate71aand front-right intermediate protruding plate72a.

When the yellow process cartridge17Y is housed in the second cartridge housing space75b, the center beam43cis positioned rearward of the rear side surface62bof the cartridge frame60bof the yellow process cartridge17Y to be spaced away therefrom in the front-rear direction. The front-left intermediate protruding plate71aand front-right intermediate protruding plate72aare positioned frontward of the front side surface61bof the cartridge frame60bso as to be spaced apart therefrom in the front-rear direction.

Incidentally, when the yellow process cartridge17Y is attached to and detached from the second cartridge housing space75b, the front side surface61bof the yellow process cartridge17Y is guided by the front-left intermediate protruding plate71aand front-right intermediate protruding plate72a.

When the magenta process cartridge17M is housed in the third cartridge housing space75c, the center beam43cis positioned frontward of the front side surface61cof the cartridge frame60cof the magenta process cartridge17M to be spaced away therefrom in the front-rear direction. The rear-left intermediate protruding plate71band rear-right intermediate protruding plate72bare positioned rearward of the rear side surface62cof the cartridge frame60cso as to be spaced apart therefrom in the front-rear direction.

Incidentally, when the magenta process cartridge17M is attached to and detached from the third cartridge housing space75c, the rear side surface62cof the magenta process cartridge17M is guided by the rear-left intermediate protruding plate71band rear-right intermediate protruding plate72b.

When the cyan process cartridge17C is housed in the fourth cartridge housing space75d, the rear beam43bis positioned rearward of the rear side surface62dof the cartridge frame60dof the cyan process cartridge17C to be spaced away therefrom in the front-rear direction. The rear-left intermediate protruding plate71band rear-right intermediate protruding plate72bare positioned frontward of the front side surface61dof the cartridge frame60dso as to be spaced apart therefrom in the front-rear direction.

Incidentally, when the cyan process cartridge17C is attached to and detached from the fourth cartridge housing space75d, the front side surface61dof the cyan process cartridge17C is guided by the rear-left intermediate protruding plate71band rear-right intermediate protruding plate72b.

When the process cartridges17are housed in the cartridge housing spaces75, respectively, a number of the beam plates43is equal to or smaller than a number of the process cartridges17. Specifically, in the first embodiment, the number of beam plates43is three, and the number of process cartridges17is four.

Focusing on the first cartridge housing space75a, the front beam43ais positioned to face the front side surface61aof the black process cartridge17K, and the other beam plates43(rear beam43band center beam43c) do not face the rear side surface62aof the black process cartridge17K.

Focusing on the second cartridge housing space75b, the center beam43cis positioned to face the rear side surface62bof the yellow process cartridge17Y, and the other beam plates43(front beam43aand rear beam43b) do not face the front side surface61bof the yellow process cartridge17Y.

Focusing on the third cartridge housing space75c, the center beam43cis positioned to face the front side surface61cof the magenta process cartridge17M, and the other beam plates43(front beam43aand rear beam43b) do not face the rear side surface62cof the magenta process cartridge17M.

Focusing on the fourth cartridge housing space75d, the rear beam43bis positioned to face the rear side surface62dof the cyan process cartridge17C, and the other beam plates43(front beam43aand center beam43c) do not face the front side surface61dof the cyan process cartridge17C.

Further, the front beam43ais positioned to face the front side surface61aof the black process cartridge17K positioned frontmost in the front-rear direction, and the rear beam43bis positioned to face the rear side surface62dof the cyan process cartridge17C positioned rearmost in the front-rear direction.

The center beam43cis positioned to face the rear side surface62bof the yellow process cartridge17Y adjacent to the black process cartridge17K positioned frontmost in the front-rear direction as well as to face the front side surface61cof the magenta process cartridge17M adjacent to the cyan process cartridge17C positioned rearmost in the front-rear direction.

(3) Operational and Technical Advantages of the Drawer Unit of the First Embodiment

(3-1) According to the printer1and drawer unit12of the first embodiment, the number of the beam plates43can be reduced when compared to a case where the beam plates43are positioned to face each of the front side surface61and rear surface side62of each process cartridge17. Hence, reduced number of components are required, thereby resulting in reduction in production costs.

Further, each beam plate43is positioned to be spaced apart from the front side surface61or rear side surface62of each process cartridge17. This structure permits deformation of the drawer frame to some extent.

As a result, the drawer frame40can have a relatively flexible structure in which deflection and distortion (twisting) are allowed to some extent at the outer position, while having a relatively rigid structure in which deflection and distortion (twisting) relative to the main casing2are restricted at the inner position.

Thus, when the drawer frame40is situated at the inner position, positioning of the photosensitive drum18, charging roller19, developing roller20, supply roller21, and thickness regulation blade22which are provided in each process cartridge17can be accurately performed relative to the main casing2. As a result, enhanced image quality can be obtained in the printer1.

(3-2) According to the printer1and drawer unit12, any one of the beam plates43is positioned to face either the front side surface61or the rear side surface62of one process cartridge17, thereby ensuring rigidity of the drawer frame40.

(3-3) According to the printer1and drawer unit12, the front beam43afaces the front side surface61(61a) of the black process cartridge17K positioned frontmost in the front-rear direction, and the rear beam43bfaces the rear side surface62(62d) of the cyan process cartridge17C positioned rearmost in the front-rear direction.

Thus, rigidity of the drawer frame40can be ensured.

Further, the front side surface61(61a) of the black process cartridge17K and rear side surface62(62d) of the cyan process cartridge17C are respectively protected by the front beam43aand rear beam43b. Thus, damages to the process cartridge17can be suppressed.

(3-4) Further, according to the printer1and drawer unit12, the center beam43cis positioned to face the rear side surface62bof the yellow process cartridge17Y adjacent to the black process cartridge17K positioned frontmost in the front-rear direction and also to face the front side surface61cof the magenta process cartridge17M adjacent to the cyan process cartridge17C positioned rearmost in the front-rear direction. That is, the center beam43cis positioned at a center of the drawer frame40in the front-rear direction and between the yellow process cartridge17Y and magenta process cartridge17M. Thus, rigidity of the drawer frame40can be ensured.

(3-5) According to the printer1and drawer unit12, the left protruding plate71and right protruding plate72can guide mounting of the process cartridges17to their proper positions in the drawer frame40. That is, even without the beam plates43, the process cartridges17can be housed properly in the drawer unit12due to the guide by the left protruding plate71and right protruding plate72.

Further, the left protruding plate71and right protruding plate72can restrict occurrence of backlash of the process cartridge17supported in the drawer frame40in the front-rear direction.

(3-6) According to the printer1and drawer unit12, the front beam43a, rear beam43b, and center beam43chave the same linear expansion coefficient. Thus, the front beam43a, rear beam43b, and center beam43ccan expand or contract substantially at the same rate as one another in length in response to a temperature change. Distortion of the beam plates43attributed to a temperature change can be restrained. As a result, deformation of the drawer frame40can be suppressed.

(3-7) According to the printer1and drawer unit12, the front beam43a, rear beam43b, and center beam43care formed of the same resin material. Thus, rigidity of the front beam43a, rear beam43b, and center beam43ccan be made uniform, resulting in enhancement of rigidity of the drawer frame40.

(3-8) According to the printer1and drawer unit12, the left side plate41and right side plate42have the same linear expansion coefficient. Thus, the left side plate41and right side plate42expand or contract substantially at the same rate as each other in length in response to a temperature change. Distortion of the left and right side plates41and42attributed to a temperature change can therefore be suppressed.

(3-9) According to the printer1and drawer unit12, the left side plate41and right side plate42are formed of the same resin material. Thus, rigidity of the left side plate41and right side plate42can be made uniform, resulting in enhancement of rigidity of the drawer frame40.

(3-10) According to the printer1and drawer unit12, the left side plate41, right side plate42, front beam43a, rear beam43b, and center beam43chave the same linear expansion coefficient as one another. Thus, the left side plate41, right side plate42, front beam43a, rear beam43b, and center beam43ccan expand or contract substantially at the same rate as one another in length in response to a temperature change. Distortion attributed due to a temperature change can be suppressed.

This structure can also lead to reduction in occurrence of expansion or contraction between the left and right side plates41,42and each beam plate43(front, rear, center beams43a,43b,43c). As a result, backlash of the left and right side plates41and42relative to each beam plate43(front, rear, center beams43a,43b,43c) can be suppressed.

3. Drawer Unit of the Second Embodiment

Next, detailed constructions of a drawer unit112according to a second embodiment of the present invention will be described with reference toFIG. 3. In the following description, like parts and components are designated by the same reference numerals with those of the first embodiment to avoid duplicating description.

In the drawer unit12of the first embodiment, the drawer frame40has the left side plate41, right side plate42, front beam43a, rear beam43b, and center beam43c.

The drawer unit112of the second embodiment has a drawer frame140configured of the left side plate41, the right side plate42, a front intermediate beam43dand a rear intermediate beam43e.

Specifically, the left side plate41of the second embodiment has a front-left end protruding plate71c, a center-left protruding plate71d, and a rear-left end protruding plate71e, as the left protruding plates71. The front-left end protruding plate71cprotrudes rightward from a front end portion of the left side plate41. The center-left protruding plate71dprotrudes rightward from a center portion of the left side plate41. The rear-left end protruding plate71eprotrudes rightward from a rear end portion of the left side plate41. The rear-left end protruding plate71ehas a thickness larger than that of the front-left end protruding plate71cin the front-rear direction.

The right side plate42of the second embodiment has a front-right end protruding plate72c, a center-right protruding plate72d, and a rear-right end protruding plate72e, as the right protruding plate72. The front-right end protruding plate72cprotrudes leftward from a front end portion of the right side plate42. The center-right protruding plate72dprotrudes leftward from a center portion of the right side plate42. The rear-right end protruding plate72eprotrudes leftward from a rear end portion of the right side plate42. The rear-right end protruding plate72ehas a thickness larger than that of the front right end protruding plate72cin the front-rear direction.

The front-left end protruding plate71cand front-right end protruding plate72care positioned to be aligned with each other in the left-right direction. Similarly, the center-left protruding plate71dand center-right protruding plate72dare positioned to be aligned with each other in the left-right direction, and the rear-left end protruding plate71eand rear-right end protruding plate72eare positioned to be aligned with each other in the left-right direction.

The front intermediate beam43dis a flat plate having a substantially rectangular shape extending in the left-right direction in a front view. The front intermediate beam43dconnects the respective front intermediate positions of the left side plate41and right side plate42, each front intermediate position being positioned between the front end portion and the center portion of the left side plate41or the right side plate42.

The rear intermediate beam43eis a flat plate having a substantially rectangular shape extending in the left-right direction in a front view. The rear intermediate beam43econnects the respective rear intermediate positions of the left side plate41and right side plate42, each rear intermediate position being positioned between the rear end portion and the center portion of the left side plate41or the right side plate42.

The front intermediate beam43d, front-left end and front-right end protruding plates71cand72c, and left and right side plates41and42between the front-left end and front-right end protruding plates71cand72cdefine the first cartridge housing space75aextending in the left-right direction. The first cartridge housing space75ais positioned frontmost in the front-rear direction among the four cartridge housing spaces75, as in the first embodiment. The first cartridge housing space75ahouses a black process cartridge117K of the second embodiment, instead of the black process cartridge17K. The black process cartridge117K has a front surface161aand a gripping part86formed on the front surface161aat a center thereof in the left-right direction to protrude frontward therefrom.

The front intermediate beam43d, center-left and center-right protruding plates71dand72d, and left and right side plates41and42between the center-left and center-right protruding plates71dand72ddefine the second cartridge housing space75bextending in the left-right direction. The second cartridge housing space75bis positioned second from the front in the front-rear direction among the four cartridge housing spaces75. The second cartridge housing space75bhouses the yellow process cartridge17Y.

The rear intermediate beam43e, center-left and center-right protruding plates71dand72d, and left and right side plates41and42between the center-left and center-right protruding plates71dand72ddefine the third cartridge housing space75cextending in the left-right direction. The third cartridge housing space75cis positioned second from the rear in the front-rear direction among the four cartridge housing spaces75. The third cartridge housing space75chouses the magenta process cartridge17M.

The rear intermediate beam43e, rear-left end and rear-right end protruding plates71eand72e, and left and right side plates41and42between the rear-left end and rear-right end protruding plates71eand72edefine the fourth cartridge housing space75dextending in the left-right direction. The fourth cartridge housing space75dis positioned rearmost among the four cartridge housing spaces75in the front-rear direction. The fourth cartridge housing space75dhouses the cyan process cartridge17C.

Focusing on the first cartridge housing space75a, the front intermediate beam43dis positioned to face the rear side surface62aof the black process cartridge117K, and the other beam plate43(rear intermediate beam43e) does not face the front side surface161aof the black process cartridge117K.

Focusing on the second cartridge housing space75b, the front intermediate beam43dis positioned to face the front side surface61bof the yellow process cartridge17Y, and the other beam plate43(rear intermediate beam43e) does not face the rear side surface62bof the yellow process cartridge17Y.

Focusing on the third cartridge housing space75c, the rear intermediate beam43eis positioned to face the rear side surface62cof the magenta process cartridge17M, and the other beam plate43(front intermediate beam43d) does not face the front side surface61cof the magenta process cartridge17M.

Focusing on the fourth cartridge housing space75d, the rear intermediate beam43eis positioned to face the front side surface61dof the cyan process cartridge17C, and the other beam plate43(front intermediate beam43d) do not face the rear side surface62dof the cyan process cartridge17C.

According to the drawer unit112of the second embodiment, any one of the beam plates43(front intermediate beam43dor rear intermediate beam43e) is positioned to face the front side surface61or rear side surface62of one process cartridge17. Rigidity of the drawer frame140can be thus ensured. Further, the drawer frame140and process cartridges17supported by the drawer frame140can be reliably moved between the inner position (at which the drawer unit112is positioned inside the main casing2) and outer position (at which the drawer unit112is positioned outside the main casing2) by holding the holding part86of the black process cartridge117K.

4. Drawer Unit of the Third Embodiment

Next, detailed constructions of a drawer frame240A-240C according to a third embodiment of the present invention will be described with reference toFIGS. 4A to 4C. In the following description, like parts and components are designated by the same reference numerals with those of the forgoing embodiments to avoid duplicating description.

The drawer frame40of the first embodiment has three beam plates43(front beam43a, rear beam43band center beam43c). However, the number of beam plates43is not necessarily limited to three, as long as the number of beam plates43is equal to or smaller than the number of process cartridges17provided in the drawer frame40.

As an example, in the third embodiment, each drawer frame240A-240C has four beam plates43, as illustrated inFIGS. 4A to 4C.

Referring toFIG. 4A, in the drawer frame240A, the front intermediate beam43d, center beam43c, rear intermediate beam43e, and rear beam43bare provided to connect between the left side plate41and right side plate42.

In the drawer frame240A, the left side plate41has the front-left end protruding plate71c, and the right side plate42has the front-right end protruding plate72c.

Referring toFIG. 4B, in the drawer frame240B, the front beam43a, front intermediate beam43d, center beam43c, and rear intermediate beam43eare provided to connect between the left side plate41and right side plate42. InFIG. 4B, the gripping part46is omitted.

In the drawer frame240B, the left side plate41has the rear-left end protruding plate71e, and the right side plate42has the rear-right end protruding plate72e.

Referring toFIG. 4C, in the drawer frame240C, the front beam43a, front intermediate beam43d, rear intermediate beam43e, and rear beam43bare provided to connect between the left side plate41and right side plate42. InFIG. 4C, the gripping part46is omitted.

In the drawer frame240C, the left side plate41has the center-left protruding plate71d, and the right side plate42has the center-right protruding plate72d.

5. Drawer Unit of the Fourth Embodiment

Next, detailed constructions of a drawer frame340A-340G according to a fourth embodiment of the present invention will be described with reference toFIGS. 5A to 5G. In the following description, like parts and components are designated by the same reference numerals with those of the forgoing embodiments to avoid duplicating description.

The drawer frame340A-340G of the fourth embodiment includes three beam plates43or less than three less beam plates43.

In the drawer frame340A illustrated inFIG. 5A, three beam plates43(i.e., the front intermediate beam43d, center beam43c, and rear intermediate beam43e) connect the left side plate41and right side plate42.

In the drawer frame340A, the left side plate41has the front-left end protruding plate71cand rear-left end protruding plate71e, and the right side plate42has the front-right end protruding plate72cand rear-right end protruding plate72e.

In the drawer frame340B illustrated inFIG. 5B, three beam plates43(i.e., the front intermediate beam43d, rear intermediate beam43e, and rear beam43b) connect the left side plate41and right side plate42.

In the drawer frame340B, the left side plate41has the front-left end protruding plate71cand center-left protruding plate71d, and the right side plate42has the front-right end protruding plate72cand center-right protruding plate72d.

In the drawer frame340C illustrated inFIG. 5C, three beam plates43(i.e., the front beam43a, center beam43c, and rear intermediate beam43e) connect the left side plate41and right side plate42. InFIG. 5C, the gripping part46is omitted.

In the drawer frame340C, the left side plate41has the front-left intermediate protruding plate71aand rear-left end protruding plate71e, and the right side plate42has the front-right intermediate protruding plate72aand rear-right end protruding plate72e.

In the drawer frame340D illustrated inFIG. 5D, two beam plates43(i.e., the front beam43aand rear beam43b) connect the left side plate41and right side plate42. InFIG. 5D, the gripping part46is omitted.

In the drawer frame340D, the left side plate41has the front-left intermediate protruding plate71a, center-left protruding plate71d, and rear-left intermediate protruding plate71b, and the right side plate42has the front-right intermediate protruding plate72a, center-right protruding plate72d, and rear-right intermediate protruding plate72b.

In the drawer frame340E illustrated inFIG. 5E, two beam plates43(i.e., the center beam43cand rear beam43b) connect the left side plate41and right side plate42.

In the drawer frame340E, the left side plate41has the front-left end protruding plate71c, front-left intermediate protruding plate71aand rear-left intermediate protruding plate71b, and the right side plate42has the front-right end protruding plate72c, front-right intermediate protruding plate72aand rear-right intermediate protruding plate72b.

In the drawer frame340F illustrated inFIG. 5F, one beam plate43(i.e., the center beam43c) connects the left side plate41and right side plate42.

In the drawer frame340F, the left side plate41has the front-left end protruding plate71c, front-left intermediate protruding plate71a, rear-left intermediate protruding plate71b, and rear-left end protruding plate71e, and the right side plate42has the front-right end protruding plate72c, front-right intermediate protruding plate72a, rear-right intermediate protruding plate72b, and rear-right end protruding plate72e.

In the drawer frame340G illustrated inFIG. 5G, one beam plate43(i.e., the rear beam43b) connects the left side plate41and right side plate42.

In the drawer frame340G, the left side plate41has the front-left end protruding plate71c, front-left intermediate protruding plate71a, center-left protruding plate71d, and rear-left intermediate protruding plate71b, and the right side plate42has the front-right end protruding plate72c, front-right intermediate protruding plate72a, center-right protruding plate72d, and rear-right intermediate protruding plate72b.

6. Drawer Unit of the Fifth Embodiment

Next, detailed constructions of a drawer unit412(having a drawer frame440) according to a fifth embodiment of the present invention will be described with reference toFIG. 6. In the following description, like parts and components are designated by the same reference numerals with those of the forgoing embodiments to avoid duplicating description.

The drawer unit12of the first embodiment includes four process cartridges17. However, the number of process cartridges17may be fewer than four. As an example, the drawer unit412of the fifth embodiment includes three process cartridges17instead of four process cartridges17, as shown inFIG. 6.

Specifically, the drawer frame412has the left side plate41, right side plate42, front beam43a, and an intermediate beam43f.

Further, the left side plate41has an intermediate-left protruding plate71fand the rear-left end protruding plate71e. The intermediate-left protruding plate71fprotrudes rightward from a right surface of the left side plate41at a position substantially one-third of the left side plate41from the front end thereof in the front-rear direction.

The right side plate42has an intermediate-right protruding plate72fand the rear-right end protruding plate72e. The intermediate-right protruding plate72fprotrudes leftward from a left surface of the right side plate42at a position substantially one-third of the right side plate42the front end portion thereof in the front-rear direction.

The intermediate beam43fconnects between a general center of the left side plate41and a general center of the right side plate42in the front-rear direction, the general center of the left side plate41being a general center between the intermediate-left protruding plate71fand the rear-left end protruding plate71eand the general center of the right side plate42being a general center between the intermediate-right protruding plate72fand the rear-right end protruding plate72ein the front-rear direction.

7. Drawer Unit of the Sixth Embodiment

Next, detailed constructions of a drawer frame540according to a sixth embodiment of the present invention will be described with reference toFIGS. 7A and 7B. In the following description, like parts and components are designated by the same reference numerals with those of the forgoing embodiments to avoid duplicating description.

As illustrated inFIG. 7A, the drawer frame540according to the sixth embodiment is generally identical to the drawer frame340D illustrated inFIG. 5D, but drawer frame540is further provided with a bar steel member7171.

That is, the drawer frame540includes the left side plate41, right side plate42, the front beam43aand rear beam43b. The front beam43aand rear beam43bconnect between the left side plate41and right side plate42. The left side plate41has the front-left intermediate protruding plate71a, center-left protruding plate71d, and rear-left intermediate protruding plate71b, and the right side plate42has the front-right intermediate protruding plate72a, center-right protruding plate72d, and rear-right intermediate protruding plate72b.

Further, each of the center-left protruding plate71dand center-right protruding plate72dis formed with an engagement groove110. The engagement grooves110are in a form of a bored hole recessed into an upper end face of the center-left protruding plate71dand upper end face of the center-right protruding plate72d, respectively.

As illustrated inFIG. 7B, the bar steel member97is formed of a bar-like shaped steel extending in the left-right direction. The bar steel member97has a length (thickness) smaller than the beam plates43(front beam43aand rear beam43b) with respect to the front-rear direction. More specifically, the bar steel member97has a substantial U-shape and includes a body portion97a, a left engagement portion97b, and a right engagement portion97c.

The body portion97ahas a round bar shape extending in the left-right direction and has a length spanning between the center-left protruding plate71dand the center-right protruding plate72din the left-right direction.

The left engagement portion97bhas a round bar shape and extends downward from a left end portion of the body part97a. The right engagement portion97chas a round bar shape and extends downward from a right end portion of the body part97a.

As illustrated inFIG. 7A, the left engagement portion97bis engaged with the engagement groove110of the center-left protruding plate71d, and the right engagement portion97cis engaged with the engagement groove110of the center-right protruding plate72d.

With this configuration, although the drawer frame540is not provided with the center beam43c, the bar steel member97in place of the center beam43ccan restrict a left-right distance between the left side plate41and right side plate42from getting longer than a left-right distance that could have been maintained if the center beam43cconnects between the left side plate41and right side plate42.

In other words, the left-right distance between the left side plate41and right side plate42is suppressed from becoming longer by the bar steel member97. The left-right distance between the left side plate41and right side plate42can be thus properly maintained.

As a result, when the process cartridges17are mounted in the drawer frame540, distances between each process cartridges17and each side plate (the left and right side plates41,42) is maintained as prescribed, thereby suppressing backlash of the process cartridges17relative to the left and right side plates41and42.

The bar steel member97is engaged with the center-left protruding plate71dand center-right protruding plate72din the sixth embodiment, but the bar steel member97may be engaged with any one of pairs of the left protruding plates71and right protruding plates72depending on an intended use.

For example, the bar steel member97may be engaged with the pair of the front-left intermediate protruding plate71aand front-right intermediate protruding plate72aor the pair of rear-left intermediate protruding plate71band rear-right intermediate protruding plate72b.

8. Drawer Unit of the Seventh Embodiment

A drawer frame640according to a seventh embodiment of the present invention will be described with reference toFIG. 8.

The drawer frame640of the seventh embodiment has the same structure as the drawer frame540of the sixth embodiment except the97except the bar steel member97. That is, in the drawer frame640, a wire rod99is provided instead of the bar steel member97. In the drawer frame640, the wire rod99is engaged with the center-left protruding plate71dand center-right protruding plate72d.

Specifically, each of the center-left protruding plate71dand center-right protruding plate72dhas an engagement portion120. The engagement portions120are formed in a front surface of the center-left protruding plate71dand a front surface of the center-right protruding plate72d, respectively.

The wire rod99is formed of a wire extending in the left-right direction and has a length spanning between the center-left protruding plate71dand center-right protruding plate72d.

A left end portion of the wire rod99is engaged with the engagement portion120of the center-left protruding plate71d, and a right end portion of the wire rod99is engaged with the engagement portion120of the center-right protruding plate72d.

Providing the wire rod99in the drawer frame640can be simple and easy. At the same time, the same technical advantages as those of the sixth embodiment can be achieved.

Incidentally, the wire rod99may be engaged with any one of pairs of the left protruding plates71and right protruding plates72, depending on an intended use.

For example, the wire rod99may be engaged with the pair of the front-left intermediate protruding plate71aand front-right intermediate protruding plate72aor the pair of rear-left intermediate protruding plate71band rear-right intermediate protruding plate72b.

9. Drawer Unit of the Eighth Embodiment

A drawer frame740according to an eighth embodiment will be described next with reference toFIG. 9. In the following description, like parts and components are designated by the same reference numerals with those of the first embodiment to avoid duplicating description

In the drawer unit12of the first embodiment, the left side plate41, right side plate42, and three beam plates43integrally constitute the drawer frame40as a single member.

However, as illustrated inFIG. 9, in the drawer frame740according to an eighth embodiment, the left side plate41, right side plate42, and three beam plates43are formed as separate members and constitute the drawer frame40when assembled to one another.

Specifically, in a drawer unit712of the eighth embodiment, the drawer frame740has the left side plate41, right side plate42, and three beam plates43(front beam43a, rear beam43band center beam43c) each as an independent member.

Each of the three beam plates43is screw-fixed to the left side plate41and right side plate42by screws102.

The drawer unit712as assembled above can also achieve the same operational and technical advantages as those of the drawer unit12of the first embodiment.

10. Variations and Modifications

In the depicted embodiments, the left side plate41, right side plate42, and beam plates43are formed of the same resin material. However, the beam plates43may be made of a material different from those of the left side plate41and right side plate42. For example, the left and right side plates41,42may be formed of a resin, while the beam plates43may be made of a metal steel plate.