US20130154180A1

US20130154180A1 - Image forming apparatus

Info

Publication number: US20130154180A1
Application number: US13/711,353
Authority: US
Inventors: Naoichi Asakura; Kouki Muramoto
Original assignee: Konica Minolta Business Technologies Inc
Current assignee: Konica Minolta Business Technologies Inc
Priority date: 2011-12-15
Filing date: 2012-12-11
Publication date: 2013-06-20
Also published as: JP2013124175A; CN103159050B; CN103159050A

Abstract

An image forming apparatus includes a sheet cassette, a sheet feed roller, and a separating blade. An image forming section and a sheet conveying path for conveying a sheet to the image forming section are placed in a position within the width of a cassette body defined in a sheet feeding direction and above the cassette. The tip of the separating blade is placed in a portion of stacked sheets accommodated in the cassette between a front end portion and a rear end portion of the cassette. The sheet feed roller is placed in a position between the front end portion and the rear end portion of the cassette and apart from the tip of the separating blade toward the rear end portion.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2011-274864 filed on Dec. 15, 2011, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to an image forming apparatus and more particularly to an image forming apparatus provided with a sheet feeding device configured to separate sheets one by one from stacked sheets and convey each sheet to an image forming section.
2. Description of Related Art
Some image forming apparatus each include an image forming section to form an image on a sheet and a sheet feeding device (feeder) to feed the sheet to the image forming section. Many of sheet feeding devices are each provided with a separating mechanism for separating sheets one by one from stacked sheets to feed one sheet each.
For example, JP-A-3(1991)-51230 discloses a sheet feeding device configured to rotate a separating roller in a reverse direction (see an arrow Tb in FIG. 1 of JP-A-3(1991)-51230) and thereafter rotate the separating roller in a forward (normal) direction (see an arrow Ta in FIG. 1 of JP-A-3(1991)-51230) to convey a sheet. This is to separate an uppermost sheet from stacked sheets and convey the sheet along a sheet conveying path. JP-A-2002-87606 discloses a sheet feeding device including an auxiliary roller which rotates in a reverse direction and thereafter rotates in a forward direction (see FIG. 2 and others in JP-A-2002-87606). This is to prevent double sheet feeding.
In recent years, meanwhile, there has been an increasing demand for downsizing of an image forming apparatus to address environmental issues or save office space. However, the width of a conventional image forming apparatus is, as shown in FIG. 1, equal to or larger than the sum (“A+B” in FIG. 1) of the width (see a dimension line A in FIG. 1) of a sheet cassette and the width (see a dimension line B in FIG. 1) of a section wherein a sheet conveying path is contained. Accordingly, the size of the image forming apparatus in a width direction has a lower limit at this width (A+B). The same applies to sheet feeding devices disclosed in JP-A-3(1991)-51230 and JP-A-2002-87606.
The present invention has been made to solve the above conventional problems and has a purpose to provide an image forming apparatus including a sheet feeding device configured to sequentially feed sheets one by one from stacked sheets and ensure a reduced width of the image forming apparatus.

SUMMARY OF THE INVENTION

To achieve the above purpose, one aspect of the invention provides an image forming apparatus comprising: a sheet cassette configured to accommodate stacked sheets; a separating member configured to separate an uppermost sheet from the stacked sheets accommodated in the sheet cassette; a sheet feed roller configured to feed the uppermost sheet from the stacked sheets accommodated in the sheet cassette; an image forming section configured to form an image on the sheet fed from the sheet cassette; and a sheet conveying path placed between the sheet cassette and the image forming section, wherein the image forming section and the sheet conveying path are placed in a position within a width of the sheet cassette defined between a front end and a rear end of the cassette in a sheet feeding direction and above the sheet cassette, the separating member has a tip to be placed to contact with a portion of the stacked sheets accommodated in the sheet cassette between the front end and the rear end of the cassette, and the sheet feed roller is placed in a position between the front end and the rear end of the sheet cassette and apart from the tip of the separating member toward the rear end of the sheet cassette. In this image forming apparatus, the overall or full width of the image forming apparatus does not greatly differ from the width of the sheet cassette. That is, downsizing of the image forming apparatus is achieved.
According to the present invention, there is provided an image forming apparatus including a sheet feeding device configured to sequentially feed sheets one by one from stacked sheets and ensure a reduced width of an image forming apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration view to explain a conventional image forming apparatus;

FIG. 2 is a schematic configuration view to explain an image forming apparatus in an embodiment of the present invention;

FIG. 3 is a schematic configuration view to explain a sheet cassette in the embodiment;

FIG. 4 is a view to illustrate conveying rollers and a separating blade in the embodiment;

FIG. 5 is a view (Part 1) to show a sheet feeding operation of the image forming apparatus in the embodiment;

FIG. 6 is a view (Part 2) to show the sheet feeding operation of the image forming apparatus in the embodiment;

FIG. 7 is a view (Part 3) to show the sheet feeding operation of the image forming apparatus in the embodiment;

FIG. 8 is a view to show a case where a number of sheets are loaded in a sheet cassette in the embodiment;

FIG. 9 is a view to show a case where only one sheet is loaded in the sheet cassette in the embodiment;

FIG. 10 is a schematic configuration view (Part 1) to explain a sheet cassette in a modified example;

FIG. 11 is a schematic configuration view (Part 2) to explain a sheet cassette in a modified example; and

FIG. 12 is a schematic configuration view (Part 3) to explain a sheet cassette in a modified example.

DESCRIPTION OF EMBODIMENTS

A detailed description of a preferred embodiment of the present invention will now be given referring to the accompanying drawings. In the present embodiment, the invention is applied to a black and white printer.

1. Image Forming Apparatus

An image forming apparatus 100 is a black and white printer having a schematic configuration shown in FIG. 2. This image forming apparatus 100 includes a sheet cassette 10, a sheet feed roller 14, a sheet conveying path 20, an image forming section 30, a transfer roller 40, a fixing unit 50, a pair of sheet discharging roller 61, a discharge tray 62, a motor M, and a controller 90.
The sheet cassette 10 is arranged to accommodate stacked sheets and feed an uppermost sheet from the stacked sheets. A fed sheet is conveyed along the sheet conveying path 20 to the image forming section 30. The details of this configuration will be explained later. The sheet cassette 10 can be pulled out to the front side (near side) in FIG. 2 from the image forming apparatus 100. In the present embodiment, hereinafter, a right-to-left direction to the image forming apparatus 100 in FIG. 2 is referred to as a width direction. A maximum size of the image forming apparatus 100 in the width direction is referred to as a “full width W” and a length of the sheet cassette 10 from a front end to a rear end in a sheet feeding direction is referred to as a “width W1”
The sheet feed roller 14 is used to pick up and feed an uppermost sheet from stacked sheets loaded in the sheet cassette 10 toward the sheet conveying path 20. This sheet conveying path 20 is arranged to convey the sheet fed out from the cassette 10 toward the image forming section 30. The sheet conveying path 20 is provided with a timing sensor 21 to determine the timing at which a sheet is fed to the transfer roller 40. The sheet conveying path 20 is located in a position within the width W1 of the cassette 10 and above the cassette 10. Accordingly, the full width W of the image forming apparatus 100 in the present embodiment is not so greatly different from the width W1 of the cassette 10. In other words, the image forming apparatus 100 in the present embodiment is smaller in size than the conventional image forming apparatus.
The image forming section 30 is arranged to form an image on a sheet. This image forming section 30 includes a photoconductor drum 31, a charging unit 32, an exposing unit 33, and a developing unit 34, and a cleaner 35. The photoconductor drum 31 is an image carrier to carry a toner image thereon. This drum 31 is therefore rotated in a direction indicated by an arrow D2 in FIG. 2. The charging unit 32 is arranged to uniformly charge the surface of the drum 31. The exposing unit 33 is configured to form an electrostatic latent image on the surface of the drum 31. The developing unit 34 is arranged to impart toner to the electrostatic latent image on the surface of the drum 31. The cleaner 35 is used to remove untransferred residual toner from the drum 31.
The transfer roller 40 is a transfer member for transferring a toner image formed on the photoconductor drum 31 to a sheet. The sheet having the toner image transferred thereon is then transported along the sheet conveying path 20 in a direction indicated by an arrow D1 in FIG. 2.
The fixing unit 50 is arranged to fix the transferred toner image on the sheet. The pair of discharging rollers 61 are arranged to discharge the sheet having the toner image fixed thereon to the discharge tray 62. This tray 62 is a tray for receiving the sheet having the toner image fixed thereon.
The motor M is a drive source to drive the photoconductor drum 31 and various rollers to rotate. The sheet feed roller 14 and conveying rollers 17 mentioned later are to be driven by the motor M. Each component such as the drum 31 is also to be driven by the motor M. These components are rotated in sync with the rotation of the motor M. However, the rotation speeds of the components are not necessary equal to each other because of the use of a reduction gear or the like. The controller 90 is configured to control the operation of each component of the image forming section 30 and the rotation of the motor M.
As shown in FIG. 2, the image forming section 30 and the sheet conveying path 20 are located in a position within the width W1 of the sheet cassette 10 in the image forming apparatus 100 and above the cassette 10.

2. Sheet Feeding Device

2-1. Configuration of Sheet Feed Cassette
The configuration of the sheet cassette 10 will be explained below. FIG. 3 is a schematic configuration view to explain the sheet cassette 10. Specifically, this cassette 10 is configured to separate an uppermost sheet P1 from stacked sheets P and sequentially feed one sheet each to the sheet conveying path 20. Herein, an end portion of the sheet P1, which becomes the head (leading edge) of the sheet P1 during conveyance to the image forming section 30, is referred to as a leading end PT. The other end portion of the sheet P1, which becomes the tail (bottom edge) of the sheet P1 during conveyance to the image forming section 30, is referred to as a rear end PE. As shown in FIG. 3, the sheet cassette 10 includes a cassette body 11, a lifting spring 12, and a lifting plate 13.
The cassette body 11 is a sheet feed case for accommodating stacked sheets P. The cassette body 11 has a bottom plate 11 a, a front end portion 11T, and a rear end portion 11E. The front end portion 11T is a side wall of the cassette body 11 on a side facing the leading end PT of the sheet P1 before conveyance (in a loaded state). The rear end portion 11E is a side wall of the cassette body 11 on the other side facing the rear end PE of the sheet P1 before conveyance (in the loaded state).
The rear end portion 11E of the cassette body 11 includes a slanted surface 11 b. This slanted surface 11 b is slanted from the bottom plate 11 a to an upper end of the rear end portion 11E so that the rear end portion 11E is more apart from the front end portion 11T of the cassette body 11 with distance from the bottom plate 11 a. The slanted surface 11 b can function, as mentioned later, to guide the sheet P1 moved back by the sheet feed roller 14 to be warped or curved upward from the sheet cassette 10. The lifting spring 12 is arranged to lift up the portions of the stacked sheets P near the leading end PT by way of the lifting plate 13. This lifting plate 13 is a sheet loading section to actually load thereon the stacked sheets P.
2-2. Sheet Feed Roller, Guide Member, and others
The sheet feeding device includes the sheet feed roller 14 and the guide member 15 in addition to the sheet cassette 10. The sheet feed roller 14 and the guide member 15 are provided in a main body of the image forming apparatus 100 and are not allowed to be pulled out together with the sheet cassette 10. The sheet feed roller 14 is placed in a position upstream from the guide member 15 and a separating blade 16 mentioned later in a sheet conveying path. Further, the sheet feed roller 14 is located between the front end portion 11T and the rear end portion 11E of the cassette body 11 and somewhat apart from the tip of the separating blade 16 toward the rear end portion 11E. The sheet feed roller 14 is configured to, under the control of the controller 90, rotate in a forward (normal) direction (indicated by an arrow DN in FIG. 3) to move forward the sheet P1 to the sheet conveying path 20 and rotate in a reverse direction (indicated by an arrow DR in FIG. 3) to move backward the sheet P1 from the sheet conveying path 20.
The guide member 15 is an element for guiding conveyance of the sheet P1 toward the sheet conveying path 20. The guide member 15 includes the separating blade 16 and the conveying rollers 17 a, 17 b. The blade 16 is attached to the leading end of the guide member 15 and serves as a separating element for picking up and separating the sheet P1 from the stacked sheets P. The blade 16 is placed in such a manner that the tip of the blade 16 is in contact with an uppermost surface of the stacked sheets P between the front end portion 11T and the rear end portion 11E of the cassette body 11. The conveying rollers 17 a, 17 b are arranged on the end portion of the guide member 15 opposite to the separating blade 16. The conveying rollers 17 a, 17 b serve to feed the sheet P1 fed by the sheet feed roller 14 to the sheet conveying path 20.
The guide member 15 is provided with a press-contact spring 18 that pulls the guide member 15 to swing, thereby swinging the separating blade 16 together, so that the tip of the blade 16 is urged in press-contact with the stacked sheets P in a thickness direction thereof. Unless the blade 16 presses against the stacked sheets P, there is a risk that the leading end PT of the sheet P1 moved back by the sheet feed roller 14 as mentioned later may go under the blade 16 when the sheet P1 is thereafter moved forward. It is to be noted that the press-contact spring 18 is not illustrated in FIG. 4 and subsequent.
2-3. Configuration of Guide Member
FIG. 4 is a view to illustrate the configuration of the guide member 15 in the present embodiment. As shown in FIG. 4, the separating blade 16 and the conveying rollers 17 b are configured integrally with the guide member 15. The blade 16 is used to press the stacked sheets P. In case the sheet feed roller 14 delivers two or more sheets in overlapping manner at a time, the blade 16 also serves as a member for preventing double-sheet feeding in order to convey only one uppermost sheet Pl. In the present embodiment, as shown in FIG. 4, the separating blade 16 and the conveying rollers 17 b are configured to be integral with the guide member 15. The guide member 15 is supported so as to swing about the rotation axis of the conveying rollers 17 b. However, the rotation center of the guide member 15 does not necessarily coincide with the rotation axis of the conveying rollers 17 b, and has only to be located near the end portion of the guide member 15 opposite the blade 16. Of course, the blade 16 and the conveying rollers 17 b may be configured to be separate from the guide member 15.
The guide member 15 and the separating blade 16 are each made of a resin film such as polyester film or polyethylene film. Instead, they may be made of stainless sheet or steel sheet. The blade 16 may also be made of a material with a high friction coefficient or designed in a shape subjected to surface finishing to provide a high friction coefficient. This is because such a separating blade 16 can easily separate the sheet P1 from the stacked sheets P.

3. Sheet Feeding Operation in Sheet Feeding Device

A sheet feeding operation carried out in the sheet feeding device will be explained below. As shown in FIG. 5, the sheet feed roller 14 is first rotated in the direction indicated by the arrow DR (reverse rotation) in FIG. 5. The amount of rotation with which this roller 14 is to be rotated reversely may be determined in advance. However, the amount of reverse rotation corresponds to the amount of rotation to move the leading end PT of the sheet P1 in a range between the tip of the separating blade 16 and the sheet feed roller 14. Specifically, it is necessary to hold the sheet P1 free from pressure contact with the blade 16 but in pressure contact with the sheet feed roller 14. This reverse rotation of the sheet feed roller 14 moves the uppermost sheet P1 from the stacked sheets P in a direction away from the sheet conveying path 20. Thus, the sheet P1 is substantially separated from the stacked sheets P. Then, the rear end PE of the sheet P1 bumps against the slanted surface 11 b, thereby curling or curving upward. At that time, the conveying rollers 17 a, 17 b are not rotated.
Subsequently, the sheet feed roller 14 is rotated in the direction indicated with the arrow DN (forward rotation) in FIG. 6, thus moving the uppermost sheet P1 toward the sheet conveying path 20. Therefore, the sheet P1 is separated from the stacked sheets P by the separating blade 16 and conveyed toward the sheet conveying path 20. At the timing when the leading end PT of the sheet P1 goes up onto the separating blade 16, the conveying rollers 17 a, 17 b start to rotate in the direction indicated by the arrow D3 in FIG. 6. Thus, the rotation of the rollers 17 a, 17 b has started before the leading end PT of the sheet P1 reaches the conveying rollers 17 a, 17 b.
As shown in FIG. 7, after the leading end PT of the sheet P1 passes the conveying rollers 17 a, 17 b, the sheet P1 is conveyed by the conveying rollers 17 a, 17 b and the sheet feed roller 14 into the sheet conveying path 20. At that time, the sheet feed roller 14 is rotated in the direction indicated by the arrow DN (forward rotation) in FIG. 7 and the conveying rollers 17 a, 17 b are rotated in the direction indicated by the arrow D3 in FIG. 7, respectively. When the leading end PT of the sheet P1 reaches the timing sensor 21, conveyance of the sheet P1 is temporarily stopped. In accordance with the timing of forming an image on the photoconductor drum 31, the conveying rollers 17 a, 17 b and the sheet feed roller 14 are rotated to move forward the sheet P1 to the location of the transfer roller 40. Thereafter, the sheet P1 is subjected to transfer of a toner image by the transfer roller 40.

4. Sheet Loading Amount

The number of stacked sheets P loaded on the sheet cassette 10 decreases every time image formation. Thus, the following explanation is given to changes in the angle of the separating blade 16 according to the amount of sheets loaded in the sheet cassette 10.
4-1. Full Loaded Condition
FIG. 8 illustrates a case where the stacked sheets P are loaded up to a maximum loading capacity. In this case, the lifting spring 12 is sufficiently compressed by the weight of the stacked sheets P. Accordingly, the angle OA of the lifting plate 13 to the bottom plate 11 a is not so large. At that time, the angle between the upper surface of the stacked sheets P and the separating blade 16 is an angle θ1.
4-2. Empty Condition
FIG. 9 illustrates a case where only one sheet P1 is accommodated in the sheet cassette 10. In this case, the lifting spring 12 is in almost fully elongated state. The angle θB of the lifting plate 13 to the bottom plate 11 a of this state is larger than the angle θA of the lifting plate 13 to the bottom plate 11 a in the full loaded condition. Also in this case, the separating blade 16 makes the pressing action. However, because no stacked sheets P exist under the blade 16, the separating blade 16 presses the lifting plate 13 directly. The angle θ2 between the upper surface of the sheet P1 (the lifting plate 13) and the separating blade 16 is smaller than the angle θ1 in the full loaded condition.
As explained in detail above, the sheet conveying path 20 is placed within the range of the sheet cassette 10 in the width direction and above the cassette 10. Thus, the full width of the image forming apparatus 100 in the present embodiment is not so greatly different from the width of the sheet cassette 10. That is, the size of the image forming apparatus 100 in the present embodiment is smaller than the size of the conventional image forming apparatus.

5. Modified Examples

5-1. Shape of Cassette Body
Modified examples of the present embodiment are explained below.
Although the above embodiment provides the slanted surface 11 b in the cassette body 11, the slanted surface 11 b is not necessarily provided. As shown in FIG. 10, a sheet cassette 210 with no slanted surface 11 b may also be adopted. A cassette body 211 of this cassette 210 includes a rear end portion 211E not slanted, located on a rear end side of the stacked sheets P, in addition to a bottom plate 211 a and a front end portion 211T.
As shown in FIG. 10, when the sheet feed roller 14 is reversely rotated (in a direction indicated by an arrow DR in FIG. 10), an uppermost sheet P1 is moved to the opposite side to the sheet conveying path 20. At that time, the sheet P1 bends in a curve while the rear end PE is in contact with the rear end portion 211E of the cassette body 211. This bending allows the sheet P1 to separate from the stacked sheets P. Since static electricity of the sheet P1 is somewhat released into the atmosphere, the sheet P1 is less likely to stick to the stacked sheets P again. The image forming apparatus including this sheet cassette 210 does not need the width for providing the slanted surface 11 b, and is smaller in full width than the image forming apparatus 100 of the above embodiment.
5-2. Shape of Lifting Plate
As shown in FIG. 11, as another example, a lifting plate 313 with an angular bent shape may be adopted for loading stacked sheets P instead of the lifting plate 13 shown in FIG. 3. In a sheet cassette 310, the stacked sheets P loaded on the lifting plate 313 are also bent in the form of an upward convex curve. Thus, when an uppermost sheet P1 is to be fed, this uppermost sheet P1 is easily separated and moved from the stacked sheets P. Furthermore, noise during sheet separation is low. The shape of the lifting plate may also be designed to take a round bent shape of an upward convex curve.
5-3. High Friction Member
As shown in FIG. 12, a sheet cassette 410 including a high friction member 412 may be used. This configuration is obtained by making the slanted surface 11 b of the cassette body 11 (see FIG. 3 and others) from the high friction member. Accordingly, the high friction member 412 is placed on a rear end portion 411E of the cassette body 411. Herein, the high friction member 412 is made of a material having a larger friction coefficient than that of any other portions (a bottom plate 411 a and a front end portion 411T) of the sheet cassette 410 than the slanted surface 11 b. For example, this material is selectable from cork, rubber, or the like. Thus, the separating blade 16 can easily separate an uppermost sheet P1 from the stacked sheets P.

6. Conclusion

As explained in detail above, the image forming apparatus 100 in the embodiment is configured such that the sheet feed roller 14 and the separating blade 16 to convey the sheet P1 to the section above the cassette body 11 are provided within the width W1 of the sheet cassette 10. Accordingly, there is realized the image forming apparatus 100 capable of feeding each sheet P1 sequentially from the stacked sheets P and conveying the sheet P1 to the sheet conveying path 20 located above the cassette 10.
In the image forming apparatus 100 in the embodiment, the sheet conveying path 20 is also placed in the upper section within the width W1 of the sheet cassette 10. Thus, the full width W of the image forming apparatus 100 is not so greatly different from the width W1 of the sheet cassette 10. That is, the image forming apparatus 100 is smaller in size than the conventional image forming apparatus. Such a size-reduced image forming apparatus can be achieved.
The above embodiments are mere examples not limiting the invention thereto. The present invention may be embodied in other specific forms without departing from the essential characteristics thereof. For instance, the invention is not limited to the black and white printer, but alternatively may be a color printer. Further, the invention is applicable to a copying machine as well as the printer. The invention can be applied to an image reading apparatus and an image forming apparatus configured to transmit/receive print jobs through public lines, and a combination machine. Moreover, the invention is applicable to any type of apparatus regardless of the kinds of toner and also to an image forming apparatus using a liquid color forming agent instead of toner. The guide member 15 and the separating blade 16 may be provided as an integral single piece.
The aforementioned image forming apparatus preferably includes a sheet feed roller controller configured to control the sheet feed roller to rotate reversely to feed the uppermost sheet of the stacked sheets in a direction opposite to the sheet conveying path and thereafter rotate forwardly to feed the sheet in a direction toward the sheet conveying path. This makes it possible to appropriately feed an uppermost sheet from stacked sheets.
In the aforementioned image forming apparatus, preferably, an amount of reverse rotation of the sheet feed roller to be controlled by the sheet feed roller controller is determined to an amount of rotation at which a leading end of a sheet is moved to a position between the tip of the separating member and the sheet feed roller. Thus, each sheet can be temporarily moved back to be appropriately separated from the stacked sheets, and fed forward one by one.
The aforementioned image forming apparatus preferably includes a press-contact member configured to bring the tip of the separating member into press-contact with the uppermost sheet of the stacked sheets accommodated in the sheet cassette. This configuration can prevent the leading end of each sheet to be fed from going under the separating member.
The aforementioned image forming apparatus preferably includes a conveying roller configured to convey the sheet toward the sheet conveying path, the sheet having been fed by the sheet feed roller from the stacked sheets accommodated in the sheet cassette and separated by the separating member. The separated sheet is thus delivered into the sheet conveying path.
In the aforementioned image forming apparatus, preferably, there is provided a guide member holding the separating member at one end, the guide member being configured to be rotatable about a position (axis) opposite to the separating member and to feed the sheet separated by the separating member toward the sheet conveying path, wherein the conveying roller is provided at the other end of the guide member opposite to the separating member. Thus, the separated sheet can be directed to the sheet conveying path irrespective of the amount of sheets in the sheet cassette.
The aforementioned image forming apparatus preferably includes a conveying roller controller configured to control the conveying roller to start rotation to convey the sheet toward the sheet conveying path before the leading end of the uppermost sheet of the stacked sheets accommodated in the sheet cassette reaches the conveying roller. Thus, the separated sheet can be reliably delivered into the sheet conveying path. The rotation of the conveying roller may also be started after the forward rotation of the sheet feed roller is started.
In the image forming apparatus, preferably, the sheet cassette includes a lifting plate having a bent or curved shape to load the stacked sheets in the form of an upward convex curve. This configuration makes it easy to separate an uppermost sheet from the stacked sheets.
In the image forming apparatus, preferably, the sheet cassette includes a slanted surface at the rear end, the slanted surface being so slanted as to be more apart from the front end of the sheet cassette with distance from a bottom plate of the sheet cassette. Accordingly, it is possible to prevent a sheet temporarily moved back from being folded.
In the image forming apparatus, preferably, the slanted surface is made of a high friction member having a larger friction coefficient than a material forming other portions of the sheet cassette than the slanted surface, so that separation of each sheet can be performed adequately.
The high friction member may include cork or rubber.

Reference Sings List

10, 210, 310, 410 Sheet cassette
11, 211, 411 Cassette body
11 a, 211 a, 411 a Bottom plate
11 b Slanted surface
11T, 211T, 411T Front end portion
11E, 211E, 411E Rear end portion
12 Lifting spring
13, 313 Lifting plate
14 Sheet feed roller
15 Guide member
16 Separating blade
17 a, 17 b Conveying roller
18 Press-contact spring
20 Sheet conveying path
30 Image forming section
40 Transfer roller
50 Fixing unit
61 Pair of discharging rollers
62 Discharge tray
90 Controller
100 Image forming apparatus
412 High friction member
P Stacked sheets
P1 Sheet
PT Leading end
PE Rear end

Claims

What is claimed is:

1. An image forming apparatus comprising:

a sheet cassette configured to accommodate stacked sheets;

a separating member configured to separate an uppermost sheet from the stacked sheets accommodated in the sheet cassette;

a sheet feed roller configured to feed the uppermost sheet from the stacked sheets accommodated in the sheet cassette;

an image forming section configured to form an image on the sheet fed from the sheet cassette; and

a sheet conveying path placed between the sheet cassette and the image forming section,

wherein the image forming section and the sheet conveying path are placed in a position within a width of the sheet cassette defined between a front end and a rear end of the cassette in a sheet feeding direction and above the sheet cassette,

the separating member has a tip to be placed to contact with a portion of the stacked sheets accommodated in the sheet cassette between the front end and the rear end of the cassette, and

the sheet feed roller is placed in a position between the front end and the rear end of the sheet cassette and apart from the tip of the separating member toward the rear end of the sheet cassette.

2. The image forming apparatus according to claim 1, further including a sheet feed roller controller configured to control the sheet feed roller to rotate reversely to feed the uppermost sheet of the stacked sheets in a direction opposite to the sheet conveying path and thereafter rotate forwardly to feed the sheet in a direction toward the sheet conveying path.

3. The image forming apparatus according to claim 2, wherein an amount of reverse rotation of the sheet feed roller to be controlled by the sheet feed roller controller is determined to an amount of rotation at which a leading end of a sheet is moved to a position between the tip of the separating member and the sheet feed roller.

4. The image forming apparatus according to claim 1, further including a press-contact member configured to bring the tip of the separating member into press-contact with the uppermost sheet of the stacked sheets accommodated in the sheet cassette.

5. The image forming apparatus according to claim 1, further including a conveying roller configured to convey the sheet toward the sheet conveying path, the sheet having been fed by the sheet feed roller from the stacked sheets accommodated in the sheet cassette and separated by the separating member.

6. The image forming apparatus according to claim 5, further including a guide member holding the separating member at one end, the guide member being configured to be rotatable about a position opposite to the separating member and to guide the sheet separated by the separating member toward the sheet conveying path,

wherein the conveying roller is provided at the other end of the guide member opposite to the separating member.

7. The image forming apparatus according to claim 5, further including a conveying roller controller configured to control the conveying roller to start rotation to convey the sheet toward the sheet conveying path before the leading end of the uppermost sheet of the stacked sheets accommodated in the sheet cassette reaches the conveying roller.

8. The image forming apparatus according to claim 2, further including:

a conveying roller configured to convey the sheet toward the sheet conveying path, the sheet having been fed by the sheet feed roller from the stacked sheets accommodated in the sheet cassette and separated by the separating member;

a guide member holding the separating member at one end, the guide member being configured to be rotatable about a position opposite to the separating member and to guide the sheet separated by the separating member toward the sheet conveying path,

wherein the conveying roller is provided at the other end of the guide member opposite to the separating member, and

a conveying roller controller configured to control the conveying roller to start rotation to feed the sheet toward the sheet conveying path after the sheet feed roller is started to rotate forwardly but before the leading end of the uppermost sheet of the stacked sheets accommodated in the sheet cassette reaches the conveying roller.

9. The image forming apparatus according to claim 1, wherein the sheet cassette includes a lifting plate having an angularly bent or round curved shape to load the stacked sheets in the form of an upward convex curve.

10. The image forming apparatus according to claim 1, wherein the sheet cassette includes a slanted surface at the rear end, the slanted surface being so slanted as to be more apart from the front end of the sheet cassette with distance from a bottom plate of the sheet cassette.

11. The image forming apparatus according to claim 10, wherein the slanted surface is made of a high friction member having a larger friction coefficient than a material forming other portions of the sheet cassette than the slanted surface.

12. The image forming apparatus according to claim 11, wherein the high friction member is made of cork.

13. The image forming apparatus according to claim 11, wherein the high friction member is made of rubber.