Image formation apparatus

An image formation apparatus has a belt unit and a drawer casing configured to accommodate the plurality of process units. The drawer casing is movable in a horizontal direction so that it is insertable in and/or drawable from a main body of the image formation apparatus. An openable cover for an opening formed on an end face of the drawer casing is provided. The drawer casing is arranged above an imaginary plane including the bridging surface of an endless belt, while a sheet tray is arranged below the imaginary plane. A pair of rollers is arranged on the sheet tray side with respect to the movable path and configured to feed the sheet fed from the sheet tray to the belt unit. A first guide and a second guide, which is provided opposite to the first guide with a predetermined clearance therebetween, are provided to form a sheet feed path.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 from Japanese Patent Application No. 2010-110485 filed on May 12, 2010. The entire subject matter of the application is incorporated herein by reference.

BACKGROUND

1. Technical Field

Aspects of the present invention relate to a direct tandem type image formation apparatus.

2. Related Art

Conventionally, there has been known an image formation apparatus such as one disclosed in United States Provisional Publication No. 2009/190978 A1. Such a conventional image formation apparatus is provided with a drawer casing, which accommodates a plurality of process units and is configured to be inserted in and/or drawn from a housing of the image formation apparatus, through an opening formed on the housing. In such an apparatus, a cover which can open/close the opening is provided, and a guide is provided to the cover. The guide is for guiding a printing sheet transferred from a pair of register rollers to an endless belt for feeding the printing sheet inside the image formation apparatus.

SUMMARY

According to the conventional structure as above, since the guide is for guiding the printing sheet fed from the register rollers to the endless belt, accuracy of relative positions between the guide and the photoconductive drum, and accuracy of relative positions between the guide and the belt unit should be high. Otherwise, the positioning of the printing sheet becomes inaccurate, which causes a bad effect on image quality.

According to the publication, since the guide is provided on the cover which is movable, it is difficult to obtain high accuracy in relative positions between the guide and the photoconductive drum, and between the guide and the belt unit.

In order to improve the positional accuracy, a mechanism that enables accurate positioning of the movable cover with respect to the housing may be required. However, employment of such a mechanism may increase a manufacturing cost of the image formation apparatus.

According to aspects of the invention, there is provided an image formation apparatus configured to form an image on a printing sheet in accordance with an electrophotographic image formation method, which includes a belt unit including a pair of belt rollers and an endless belt wound around the pair of belt rollers, the endless belt including a bridging surface bridging between the pair of rollers, the printing sheet being fed between the photoconductive drum and the bridging surface of the endless belt facing the photoconductive drum, a plurality of process units each having a photoconductive drum arranged to face a bridging surface of the endless belt and bear developing agent corresponding to an image, a drawer casing configured to accommodate the plurality of process units, the drawer casing being movable along a feed path which is parallel with the bridging surface of the endless belt so that the drawer case casing is insertable in and/or drawable from a main body of the image formation apparatus, an openable cover which is provided to cover an opening formed on one end face at one end in a drawing direction of the drawer casing, the openable cover being movable between an open position where the openable cover does not cover the opening and a close position where the openable cover covers the opening, a sheet tray arranged on an side opposite to the drawer casing with respect an imaginary plane that includes the bridging surface, the sheet to be fed by the belt unit being mounted on the sheet tray, a pair of rollers arranged on a sheet tray side with respect to the movable path and configured to feed the sheet fed from the sheet tray to the belt unit, a first guide provided to the drawer casing and configured to guide the sheet fed by the pair of rollers toward the bridging surface, and a second guide provided opposite to the first guide with a predetermined clearance therebetween, the second guide forming a sheet feed path in association with the first guide.

According to aspects of the invention, there is provided an image formation apparatus configured to form an image on a sheet in accordance with an electrophotographic image formation method, which includes a main body including a housing formed with an opening, and an openable cover which is movable between an open position where the openable cover uncovers the opening and a close position where the openable cover covers the opening, a plurality of process units each having a photoconductive drum bearing developing agent, a belt unit including a pair of belt rollers and an endless belt, the endless belt including a stained bridging surface tensioning between the pair of rollers and facing the photoconductive drum, the sheet being fed between the photoconductive drum and the strained bridging surface, a drawer casing accommodating the plurality of process units, the drawer casing being drawable from the main body, through the opening, along a moving path which is parallel with the strained bridging surface, a sheet tray arranged at a position opposite to the drawer casing with respect the belt unit, the sheets to be fed to the belt unit being mounted on the sheet tray, a first guide provided to the drawer casing, a second guide provided to face the first guide with a predetermined clearance therebetween, and a pair of rollers configured to feed the sheet from the sheet tray toward the first guide and the second guide, the pair of rollers being arranged in a space sandwiched between the strained bridging surface and the sheet tray.

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment according to aspects of the present invention will be described with reference to the accompany drawings.

In an image formation apparatus1(FIG. 1), an image formation unit5is accommodated. The image formation unit5is for forming an image on a printing sheet such as a recording sheet or an OHP sheet by transferring developer agent in accordance with an electrophotographic image formation method. The image formation unit5is provided with, as is well known, a plurality of process units7(7K,7Y,7M and7C), an exposure unit9and a fixer unit11.

The image formation unit1according to the embodiment is a so-called direct tandem type color image formation apparatus, and a plurality of process units (four process units)7corresponding to four color components are arranged along a sheet feed direction. Specifically, the four process units7are process units7K,7Y,7M and7C for printing black, yellow, magenta and cyan images, respectively, which are arranged in this order from the upstream side to the downstream side in the sheet feed direction which is indicated by arrow FD inFIG. 1.

In each of the drawings, directions (i.e., up and down directions, right and left directions, and front and rear directions, sheet feed direction, etc.) are indicated for the purpose of explanation. In the following description, the indicated directions in each drawing are referred to for explaining directions.

It should be noted that the four process units7K,7Y,7M and7C have substantially the same structures, and only the color of the developing agents are different. Therefore, in the following description, the process unit7will be described. The process unit7represents any one of the four process units7K,7Y,7M and7C.

The process unit7has a photoconductive drum7A, and a charger7B that charges the outer circumferential of the photoconductive drum7A. The charged photoconductive drum7A is exposed to light representing an image which is emitted by the exposure unit9so that an electrostatic latent image is formed on the outer circumferential of the photoconductive drum7A. Then, by supplying charged toner to the photoconductive drum7A, the toner is selectively adhered on the circumferential surface of the photoconductive drum7A in accordance with the latent image so that a toner image is formed thereon.

At a position opposite to the photoconductive drum7A with respect to a strained bridging surface13H of a transfer belt13A, which functions also as a sheet feed belt, a transfer roller15is provided (seeFIG. 1). It should be noted that there are four photoconductive drums7and four corresponding transfer rollers15, but in the description, one transfer roller15corresponding to one process unit7will be described for brevity. For the (image) transferring operation, the transfer roller15is applied with a voltage necessary for transferring the toner image from the photoconductive drum7A to the printing sheet.

The transfer belt13A is an endless belt wound between a driving roller13B and a driven roller13C. Both end portions (right and left end portions) of each of the driving roller13B and driven roller13C are supported by right and left belt frames13D (seeFIG. 2) which extend in a bridging direction (i.e., front and rear direction).

The strained bridging surface13H is defined as a surface of a portion of the transfer belt13A, which portion is a planar portion that bridges between the driving roller13B and the driven roller13C and faces the photoconductive drum7A with a certain tension being applied (i.e., with being strained). The bridging direction is defined as a direction parallel with a direction directed from the driving roller13B to the driven roller13C.

The plurality of the photoconductive drums7A are arranged above the strained bridging portion13H to face the strained bridging portion13H, along the sheet feed direction. Each of the photoconductive drums7A are oriented such that a rotational axis is perpendicular to the sheet feed direction. The toner image carried on the circumferential surface of the photoconductive drum7A is transferred on the sheet that is fed by the transfer belt13A.

When the toner image is transferred onto the sheet fed by the transfer belt13A, the printing sheet is fed toward a fixing unit11where heat is applied to the toner image so that the toner image is fused and fixed onto the sheet. Thereafter, the printing sheet is moved upward and discharged onto a discharge tray3A which is formed on an upper surface of the housing3.

On one side of each belt frame13D (on a front side in this embodiment), a bridge frame13E that extends between the pair of belt frames13D is provided. As above, the belt unit13includes the bridge frame13E, the transfer belt13, the driving roller13B, the driven roller13C and the belt frames13D.

The belt unit13is detachably attached to a main body of the image formation apparatus1(seeFIG. 3). The main body includes the housing3and a pair of support frames which will be described later. In order to detach the belt unit13from the main body, it is necessary to detach a drawer casing21A that accommodates the process unit7beforehand. The image formation unit5including the process units7accommodated in the drawer casing21A, the belt unit13, the sheet tray33, the feeder mechanism35, and the register rollers19are supported by the common frames (support frames), which are accommodated in the housing3.

The pair of belt frames13D is provided with positioning protrusions13F (seeFIG. 2). The positioning protrusions13F contact protrusions provided to the main body (supporting frames), not shown, so that the position of the belt unit13with respect to the main body is adjusted.

The four process units7K,7Y,7M and7C are arranged inside the drawer casing21A as shown inFIG. 1. The drawer casing21A has a substantially rectangular outlined shape viewed from the above (i.e., in a plan view) and has a pair of side walls, front wall and a rear wall. The drawer casing21A has an opened upper face, and accommodates the four processing units7K,7Y,7M and7C, which are arranged in the sheet feed direction FD.

The photoconductive drum7A and the charger7B of each process unit7extend in a direction perpendicular to the sheet feed direction, which direction is parallel with the front and rear walls of the drawer casing21A.

The drawer casing21A is attached to the main body with being guided by a rail structure provided to each of the pair of frames so that it is movable in a direction where the sheet is fed by the transfer belt13A, which is substantially parallel with the direction in which the four process units7K,7Y,7M and7C are arranged.

The drawer casing21A is supported at a lowered position at which the photoconductive drum7A contacts the transfer belt13A at a position opposite to the transfer roller15with the transfer belt13A located therebetween, when the drawer casing21A is located at an attached position inside the main body. The rail member has an inclined guiding surface which is configured such that, when a pulling force to move the drawer casing21A toward outside of the main body is applied to the drawer casing21A at the attached position, the drawer casing21A is lifted to an upper front direction so that the photoconductive drum7A is moved up away from the transfer belt13A. The rail member also has a linear guiding surface which is configured to guide the drawer casing21A, with the photoconductive drum7A being lifted and separated from the transfer belt13A, in a direction substantially parallel with an imaginary plane S1which includes the strained bridging surface13H.

With the above configuration, a moving path DL of the bottom end of the drawer casing21A (hereinafter, simply referred to as a moving path DL of the drawer casing21A) extends substantially parallel with the imaginary plane S1with a predetermined distance from the imaginary plane S1. The distance between the moving path DL and the imaginary plane S1is sufficient if the bottom end of the photoconductive drum7A does not interfere with a protection cover19A and a second guide31(described later) when the drawer casing21A is pulled out from the main body. According to the embodiment, the minimum distance may be, for example, within a range between 3 mm to 10 mm.

By opening a front cover17provided at the front face of the housing3, the drawer casing21A can be drawn through the front opening3B of the housing3. The position of the drawer casing21A when it is fully drawn from the housing3will be referred to as a drawn position. When the drawer casing21A is located at the drawn position, the four process units7are located outside the housing3. Therefore, if one or more of the processing units7run out of the toner, a user can refill the toner. Further, the user can remove the drawer casing21A for dealing with a sheet jam, or exchanging the belt unit13or a belt cleaning unit. The user can attach the drawer casing21A easily by pushing the same, from the drawn position, rearward.

As described above, according to the embodiment, it is possible to insert/remove the four process units7K,7Y,7M and7C unitarily with respect to the main body. In the following description, the four process units7K,7Y,7M and7C and other units accommodated in or attached to the drawer casing21A will be generally referred to as a drawer unit21.

According to the embodiment, the photoconductive drum(s)7A and the charger(s)7B are secured to the drawer casing21A, while container unit(s) containing the toner and cartridge(s)7D provided with developing roller(s) for supplying the toner to the photoconductive drum(s)7A are detachably attached to the process units7. Therefore, simply by exchanging the cartridge units7D, the toner can be refilled.

It should be noted that the above-described configuration is an exemplary one and can be modified in various ways. For example, each process unit7may be configured such that the developing unit is integrally secured to the drawer casing21A with only the toner container remained detachable. Alternatively, the process unit7including the photoconductive drum7A may be configured to be detachable from the drawer casing21A.

The drawer casing21A has position adjustors21B and21C provided at both ends in the drawing/inserting direction thereof (seeFIG. 6). When the drawer casing21A is inserted and attached to the main body (i.e., body frame), the position adjustors21B and21C are abut against contact portions provided to the main body, respectively, so that the position of the drawer casing21A is adjusted. When the drawer casing21A is located to its coupled position, the photoconductive drum7A and the transfer roller15face each other with the transfer belt13A located therebetween.

On a front face of the main body, the opening3B and the front cover17which is rockable between an open position where the front cover17uncovers the opening3B and a close position where the front cover17covers the opening3B are provided (seeFIGS. 1,3and4). To the front cover17, a cover tray17B is formed so that it faces a sheet supply opening17A. The cover tray17B serves as a multi-purpose sheet supply tray (hereinafter, referred to as an MP tray).

The sheet supply opening17A is formed on the front face of the housing3, which is on a front side with respect to the register roller19. Thus, the sheet supply opening17A serves as a sheet supply opening for the MP tray. The sheet is supplied to the belt unit13in a substantially flat state. The cover tray17B is secured to the front cover17and configured to be rockable so that the sheet supply opening17A can be opened/closed with the front cover17covering the opening3B. As described above, when the sheet supply opening17A is opened, the cover tray17B serves as the MP tray.

In the vicinity of the sheet supply opening17A, between the opening3B and the belt unit13, provided are a pick-up roller23which sends the uppermost sheet mounted on the cover tray17B to the pair of register rollers19, and separation roller25A and separation pad25B which separate a plurality of sheets so that the sheets is fed one by one toward the register roller19.

According to the embodiment, the register roller19has a function to adjust a timing when the sheet is transferred to the belt unit13, and a function to correct a skew (i.e. an obliquely fed condition) of the sheet transferred to the belt unit13. It is noted that the register roller19needs not have both functions, and may have only one function. Alternatively, instead of the register roller19, another roller, which simply feeds a sheet toward the belt unit13but does not have the above functions, may be provided.

In the main body, on a side opposite to the drawer casing21A with respect to the imaginary plane S1that includes the strained bridging surface13H (i.e., below the imaginary plane S1), a sheet tray33on which sheets to be fed toward the belt unit13is provided as shown inFIG. 1. The sheet tray33may be configured to be drawable in a direction parallel with a direction where the drawer casing21A is drawn. Optionally, the sheet tray33may be slidable and removable from the housing3.

The pair of register rollers19is arranged on the sheet tray side with respect to the moving path D of the drawer casing21A. That is, the pair of register rollers19is arranged substantially at the same level (height) as the imaginary plane S1or lower than the moving path D of the drawer casing21A.

On an upper side of the pair of register rollers19, that is, on the moving path D side, a protection cover19A for covering the pair of register rollers19is secured to the main body. The protection cover19A is arranged such that a surface on the moving path D side of the protection cover19A (i.e., an upper surface of the protection cover19) is lower than the moving path DL (seeFIG. 4).

Further, on the register roller side with respect to the drawer casing21A and on the belt unit side (i.e., on a lower end side in the embodiment), a first guide29that guides the sheets fed by the pair of register rollers19toward the strained bridging surface13H is provided as shown inFIG. 7. The first guide29is formed on the lower end of the front wall of the drawer casing21A as shown inFIG. 6.

On a bridge frame13E of the belt unit13, a second guide31that defines, in association with the first guide29, a sheet feed path is provided. The second guide31and the first guide29are arranged to face each other with a predetermined distance therebetween.

The second guide31has a pentroof-like inclined portion31A (seeFIG. 2) that protrudes from the belt unit13toward the pair of register roller19, and inclines downward with respect to the imaginary plane S1such that the register roller side end of the inclined portion31A is lower than the other side.

The first guide29is arranged to cover the inclined portions31A (i.e., the second guide31) entirely from the above. Specifically, the first guide29extends to cover a range from a portion corresponding to an upside of the inclined portions31A to a portion corresponding to the strained bridging portion31H of the transfer belt13A. The guide surface29A of the first guide29is curved such that the guide surface29A has an upwardly convex shape when viewed from a direction perpendicular to the sheet feed direction and to a direction of the thickness of the first guide29.

With the above configuration, the sheet is initially fed in an obliquely upward direction from the nip P1between the pair of register rollers19to proceed above the imaginary plane S1. Then, by the first guide29, the feeding direction is changed downward and the sheet is directed to the strained bridging portion13H at an acute angle (i.e., the sheet and the surface of the strained bridging portion13H form an angle less than 90 degrees).

The bridge frame13E has a gripper portion13G which is gripped by a user when the belt unit13is detached from the main body. As shown inFIG. 2, the gripper portion13G is formed as if a part of the pentroof-like inclined portion31A is cut out. It should be noted that the gripper portion13G does not have any structures which protrude from the bridge frame13E.

When the user grips the gripper portion13G, the user may insert fingers from upper side to lower side through the cutout-like portions of the gripper portion13G, and hook the fingers onto the lower surfaces of the pentroof-like inclined portion31A as shown by two-dotted line inFIG. 8.

Below the belt unit3113, the sheet feed tray33is detachably attached as shown inFIG. 1. Sheets to be fed toward the image formation unit5and transfer belt13A are mounted on the sheet feed tray33. With a feeder mechanism35, the sheets mounted on the sheet feed tray33is fed one by one toward the pair of register rollers19.

The feeder mechanism35includes, as shown inFIG. 7, a pickup roller35A configured to feed the sheets stacked on the sheet feed tray33to the pair of register rollers19, and a separation roller35B and a separation pad35C configured to separate a plurality of sheets fed from the pickup roller35A so that one sheet is fed to the pair of register rollers19at a time.

On the downstream side, in the sheet feed direction, of the separation roller35B, there are provided a pair of feed rollers36configured to feed the sheet, which has been separated by the separation roller35B and the separation pad35C, to the pair of register rollers19. The feed rollers36, the separation roller35B and the pickup roller35A are accommodated, similarly to the pickup roller23and the register rollers19, in the housing3at a location close to the front cover17and below the imaginary plane51.

According to the embodiment, the first guide29and the photoconductive drums7A are accommodated in the same member (i.e., in the drawer casing21A), accuracy of the positional relationship between the first guide29and each of the photoconductive drums7A can be made higher in comparison with a case where the first guide is provided on a front cover that is different from the drawer casing.

The drawer casing21A, which is provided with the first guide29, and the belt unit13are supported by the same frames, positional relationship therebetween can be made more accurate in comparison with a case where the first guide is provided to a front cover which is movable with respect to the frame supporting the belt unit.

According to the embodiment, the sheet fed from the register rollers19is directed to a predetermined position on the belt unit13(i.e., the transfer belt13A) as designed. Therefore, with the above configuration, deterioration of the quality of the image formed on the sheet can be suppressed.

Still further, according to the embodiment, the pair of register rollers19and the belt unit13are supported by the common frame inside the image formation apparatus. Therefore, positional relationship among the pair of register rollers19and the belt unit13can easily be made accurate.

Further, as the pair of register rollers19are is provided inside the image formation apparatus, a mechanism that transmits a rotational force to the pair of register rollers19can be made simple in comparison with a case where the pair of register rollers are is provided to the front cover.

According to the embodiment, it is unnecessary to locate the front cover accurately with respect to the main body when the front cover is closed. Therefore, the front cover can be configured to have a relatively simple structure.

According to the embodiment, the pair of register rollers are arranged on the sheet feed tray side with respect to the moving path DL of the drawer casing21A. Therefore, the drawer casing21A and the pair of register rollers do not interfere with each other when the drawer casing21A is drawn from the main body or inserted in the main body. That is, no particular structures for avoiding the interference between the drawer casing and register rollers are required. Therefore, manufacturing cost can be suppressed since the front cover can be made to have a simple structure, without detracting the operability of insertion/removal movement of the drawer casing21A.

According to the embodiment, the second guide31is provided to the belt unit13. Therefore, relative positional accuracy between the second guide31and the transfer belt13A of the belt unit13can be made higher. With this configuration, the sheet fed along the second guide31can be guided to the transfer belt13A accurately.

According to the embodiment, the drawer casing21A is arranged above the imaginary plane S1and the sheet tray33is arranged below the imaginary plane S1. The second guide31is provided with the inclined portion31A which extends from the strained bridging surface13H of the belt unit13to the pair of register rollers19, and is inclined with respect to the imaginary plane S1such that the height of the inclined portion31A is lower at a position closer to the register rollers19. The first guide29extends within a range from a position above the inclined portion31A to a position corresponding to the transfer belt13A.

According to the above configuration, a sheet fed from the pair of register rollers19toward the image formation unit5is guided by the inclined portion31A and the second guide31, and is accurately directed onto the transfer belt13A.

According to the embodiment, the gripper portion13G is formed to the bridge frame13E of the belt unit13to enable the user to remove the belt unit13easily. Therefore, even if the pair of register rollers19is provided to the main body, the user can attach/detach the belt unit13to/from the image formation apparatus easily.

According to the embodiment, the bridge frame13E is formed as if a part of the bridge frame13E has been removed in order to form the gripper portion13G. With this configuration, no part of the bridge frame13E protrudes in order to form the gripper portion. Thus, the gripper portion can be formed without causing a bad affect to sheet feeding. The gripper portion thus provided allows a user to exchange the belt unit without touching the endless belt.

According to the embodiment, the cover tray17B is provided to the front cover17. Since the pickup roller23is provided to the main body, but not to the front cover, the structure of the front cover17can be made relatively simple, and manufacturing cost can be suppressed.

According to the embodiment, the pair of register rollers19, the pickup roller23and the pickup roller35A are provided to the main body, on the front cover side. With this configuration, the pair of register rollers19, the pickup roller23and the pickup roller35A are arranged relatively closely to each other. Thus, the image formation apparatus1can be downsized and the mechanism that supplies rotational force to the rollers.

According to the embodiment, the protection cover19A is provided, which covers the moving path DL of the drawer casing21A to the pair of register rollers19. Since the protection cover19A is arranged below the moving path DL of the drawer casing21A, damage of the pair of register rollers19as they are struck by the drawer casing21A when it is drawn can be prevented.

According to the embodiment, the second guide31is provided to the belt unit13(bridge frame13E). The invention needs not be limited to such a configuration, and the second guide may be provided to, for example, the main body (i.e., housing).

The invention need not be limited to the configuration described above, and various embodiments can be provided without departing from the scope of the invention.