US20150239688A1

US20150239688A1 - Sheet feeding apparatus, image forming apparatus, and image reading apparatus

Info

Publication number: US20150239688A1
Application number: US14/613,641
Authority: US
Inventors: Yuichiro Inaba
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2014-02-26
Filing date: 2015-02-04
Publication date: 2015-08-27
Also published as: JP2015160682A

Abstract

A sheet feeding apparatus includes a stacking member configured to be rotatably provided and to stack a sheet, a feeding member configured to feed the sheet by rotating in a state of coming in contact with the sheet stacked on the stacking member, an elastic member configured to generate a pressing force to make the sheet stacked on the stacking member come in contact with the feeding member, and a restricting unit configured to abut on an uppermost sheet stacked on the stacking member and to restrict a position of the uppermost sheet to a position separated from the feeding member.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a sheet feeding apparatus which feeds a stacked sheet, an image forming apparatus which includes the sheet feeding apparatus, and an image reading apparatus which includes the sheet feeding apparatus.
2. Description of the Related Art
Conventionally, in an image forming apparatus such as a printer, a copying machine, and a facsimile machine, and an image reading apparatus such as a scanner, there is provided a sheet feeding apparatus to feed a sheet such as a recording target sheet or a sheet such as a reading target original to an image forming portion or an image reading portion.
Then, the image forming apparatus sequentially feeds the sheets stacked in a sheet cassette to the image forming portion by the sheet feeding apparatus, and forms an image on the sheet in the image forming portion. In addition, the image reading apparatus sequentially feeds the originals stacked on an original base plate by the sheet feeding apparatus to the image reading portion, and reads an original image in the image reading portion.
Herein, for example, the sheet feeding apparatus provided in the image forming apparatus may include a sheet supporting plate which is rotatable (movable) in a vertical direction (a direction of stacking sheet) and a feeding roller which feeds the sheets stacked on the sheet supporting plate. The sheet feeding apparatus is configured such that the uppermost sheet of the sheet supporting plate is pressed toward the feeding roller by a biasing member such as a spring, and in this state, the feeding roller is rotated to feed the uppermost sheet toward the image forming portion.
However, in this sheet feeding apparatus, in a case where the sheet is left under pressure of the feeding roller after a feeding operation is completed and then the sheet is fed, a plurality of sheets may be simultaneously fed to the image forming portion due to adsorption generated between the sheets. Therefore, in order to prevent that the sheets are fed in an overlapping manner, when the feeding operation is completed, the sheet supporting plate is separated from the feeding roller at a predetermined position by a lift mechanism configured by a cam or a motor.
However, in this sheet feeding apparatus, since the sheet supporting plate falls down to a certain position regardless of an amount of stacked sheets so as to separate the sheet supporting plate from the feeding roller, when the amount of stacked sheets is less, a gap between the uppermost sheet stacked on the sheet supporting plate and the feeding roller becomes wide compared to a large amount of sheets. In this way, in a case where the gap between the uppermost sheet and the feeding roller stacked on the sheet supporting plate becomes wide, when the feeding operation is performed on the next sheet, a moving amount of the sheet supporting plate is increased, and a large time loss is caused when the sheet supporting plate is pressed by a roller for feeding the sheet. In addition, since the moving amount of the sheet supporting plate becomes large, kinetic energy generated when the sheet supporting plate makes the sheet abut on the feeding roller becomes large, so that there is a problem in that a larger collision noise is generated.
Therefore, there is proposed a technology in which the sheet supporting plate is moved to make the sheet pressed by the feeding roller when the sheet is fed, and a feeding motor is reversely rotated when the feeding operation is completed, so that the sheet supporting plate is retracted from the feeding roller with respect to a press spring (see Japanese Patent No. 2601532). According to Japanese Patent No. 2601532, it is possible to separate the stacked uppermost sheet from the feeding roller to set a constant distance therebetween regardless of the amount of stacked sheets.
Japanese Patent Laid-Open No. 2008-68949 discloses a configuration in which after the sheet is fed, a moving portion (which is movable) is moved down to a position where a biasing force of the press spring of the sheet supporting plate is reduced, the sheet supporting plate is moved by the weight of the stacked sheets against the biasing force of the press spring, and thus the sheet is separated from a sheet feeding portion. According to Japanese Patent Laid-Open No. 2008-68949, since the weight of the sheet supporting plate is changed according to the amount of stacked sheets, a separating amount of the sheet supporting plate varies to keep a constant distance between the stacked uppermost sheet and the feeding roller.
However, in Japanese Patent No. 2601532 and Japanese Patent Laid-Open No. 2008-68949, after the feeding operation is completed, the sheet supporting plate is configured to be retracted from the feeding roller before the feeding operation of the next sheet, so that a driving source and a driving transmission system for transferring a driving force are required. Therefore, the configuration becomes complicated, thereby causing an increase in cost and an increase in size.
Specifically, according to the feeding apparatus disclosed in Japanese Patent No. 2601532, the feeding motor for driving the feeding roller is connected to the sheet supporting plate by a pinion and a rack. Then, when the feeding operation is performed, the feeding motor is forwardly rotated, moves to a position where the sheet supporting plate comes in press contact with the feeding roller, and after the feeding operation is completed, the feeding motor is reversely rotated, and the sheet supporting plate moves to a position to be retracted from the feeding roller. In addition, a one way clutch is disposed between the feeding motor and the feeding roller described above. By the operation of such a one way clutch, the feeding roller rotates to feed the sheet stacked on the sheet supporting plate when the feeding motor is forwardly rotated, and does not rotate when the feeding motor is reversely rotated, so that the sheet stacked on the sheet supporting plate is not damaged.
In addition, according to the feeding apparatus disclosed in Japanese Patent Laid-Open No. 2008-68949, the sheet supporting plate with the stacked sheet comes in press contact with the feeding roller by a sheet supporting plate pressing spring disposed in the moving portion which is movable by being driven from an arbitrary driving source and applies the biasing force. The above-mentioned moving portion is configured such that the sheet supporting plate moves to a first position where the sheet supporting plate is retracted from the feeding roller and no biasing force is generated, and to a second position where the sheet supporting plate comes in press contact with the feeding roller and the sheet stacked on the sheet supporting plate is fed. Furthermore, the moving portion is configured to move to a third position which is set between the first position and the second position. When the moving portion moves to the third position, the biasing force with respect to the feeding roller of the sheet supporting plate is reduced according to the amount of sheets stacked on the sheet supporting plate, and the sheet supporting plate is retracted from the feeding roller.
As described above, in Japanese Patent No. 2601532 and Japanese Patent Laid-Open No. 2008-68949, in order to configure the sheet supporting plate to be retracted from the feeding roller, the driving transmission system such as a gear train or the driving source such as the motor is additionally required. For this reason, in particular, as the feeding apparatus to be used in a low-end printer or a scanner of a small size and popular type, there are problems such that the configuration is complicated, the cost is increased, and the size is increased.

SUMMARY OF THE INVENTION

It is desirable to provide a sheet feeding apparatus having a simple and inexpensive configuration.
In order to achieve the above object, the invention provides a representative sheet feeding apparatus including: a stacking member configured to be rotatably provided and to stack a sheet; a feeding member configured to feed the sheet by rotating in a state of coming in press contact with the sheet stacked on the stacking member; an elastic member configured to generate a pressing force to make the sheet stacked on the stacking member come in press contact with the feeding member; and a restricting unit configured to abut on an uppermost sheet stacked on the stacking member and to restrict a position of the uppermost sheet to a position separated from the feeding member.
According to the invention, it is possible to provide a sheet feeding apparatus having a simple and inexpensive configuration.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating the entire image forming apparatus which includes a sheet feeding portion.

FIGS. 2A and 2B are diagrams for describing the sheet feeding portion and a sheet cassette body.

FIGS. 3A and 3B are diagrams for describing a feeding operation when the sheet feeding portion of a first example is in a full load state of sheets.

FIGS. 4A and 4B are diagrams for describing a feeding operation when the sheet feeding portion of the first example is in a light full load state of sheets.

FIGS. 5A and 5B are diagrams for describing standby states when a sheet feeding portion of a comparative example is in the full and light load states of sheets.

FIGS. 6A and 6B are diagrams for describing a sheet feeding portion of a second example.

FIG. 7 is a diagram for describing a sheet feeding portion of a third example.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, exemplary embodiments of the invention will be described in detail with reference to the drawings. However, dimensions, materials, shapes, relative arrangement of components described in the following embodiments may be suitably changed depending on a configuration or various conditions of the apparatus of the invention. Therefore, if not otherwise specified, there is no purpose of limiting the scope of the invention only to these embodiments.

First Example

An image forming apparatus which includes a sheet feeding portion as a sheet feeding apparatus according to the example will be described using FIG. 1. Herein, a printer is exemplified as the image forming apparatus, which includes the sheet feeding portion to feed a sheet such as a recording sheet serving as a recording target. FIG. 1 is a schematic cross-sectional view of the image forming apparatus which includes the sheet feeding portion.

[Image Forming Apparatus]

In FIG. 1, an apparatus body 1 of the image forming apparatus and an image forming portion 1B which forms an image on a sheet such as a recording target sheet are illustrated. The sheet feeding portion as the sheet feeding apparatus is disposed below the image forming portion 1B. Further, the image forming portion 1B is provided with a laser scanner 50, an image forming process unit which includes a photosensitive drum 49 a as an image bearing member, and a transfer roller 49 b which transfers a toner image formed on the photosensitive drum 49 a onto a sheet S.
Further, after the toner image formed on the photosensitive drum 49 a is transferred onto the sheet S by the transfer roller 49 b in the image forming portion 1B, the toner image on the sheet S is fixed by a fixing device 51. Then, after the toner image is fixed by the fixing device 51, the sheet S are sequentially discharged and stacked onto a discharge tray 54 which is provided on the apparatus body.
The sheet feeding portion includes a sheet cassette 2 serving as a sheet storage portion to stack and store the sheet, and a feeding roller 3 serving as a sheet feeding member to feed the sheet S stored in the sheet cassette 2.
Furthermore, on a downstream side in the conveying direction of the feeding roller 3, a separation roller 5 serving as a sheet separation member is provided to come in press contact with the feeding roller 3, and a separation unit serving as a sheet separation portion is provided to separate the sheets S fed out of the feeding roller 3 one by one. Further, the separation roller 5 is pressed by a separation spring 24 in the separation unit, and comes in press contact with the feeding roller 3 by pressure of the separation spring 24, so that the sheets S can be separated one by one.
Further, in the example, the sheet cassette 2 is guided and instructed by a guide (not illustrated) serving as a guide instruction portion, and is drawn out in the sheet conveying direction. In the sheet cassette 2, a sheet supporting plate 6 serving as a stacking member to stack the sheet S is provided to be rotated about a rotation center 11 in the vertical direction. Then, a sheet supporting plate spring 10 serving as an elastic member is disposed on the lower side of the sheet supporting plate 6. The sheet supporting plate spring 10 generates a pressing force to make the sheet supporting plate 6 come in press contact with the feeding roller 3.
In addition, the separation unit which includes the separation roller 5 and the separation spring 24 is also provided in the sheet cassette 2. With such a configuration, when the sheet cassette 2 is detached or attached, the separation unit and the sheet supporting plate 6 is moved integrally with the sheet cassette 2 in a state where the feeding roller 3 is left in the apparatus body.
Herein, the uppermost sheet stacked in the sheet supporting plate 6 is restricted in its position by a restricting unit 4 which abuts on the uppermost sheet to restrict the position of the uppermost sheet to a position separated from the feeding roller 3. The restricting unit 4 includes a sheet supporting plate auxiliary member 12 serving as a restricting portion and a cam 14 serving as a moving portion as illustrated in FIGS. 2A and 2B, and the detailed configuration will be described below.
The feeding roller 3 is provided in the apparatus body to be rotated, and comes in press contact with an uppermost sheet S1 stacked on the sheet supporting plate 6 during a feeding operation and abuts on the separation roller 5 on the downstream side in the sheet feeding direction.
Then, in such a configuration of the apparatus body 1, when a signal indicating a sheet feeding start is transmitted from a controller unit (not illustrated), the feeding roller 3 receives a driving force of a driving motor (not illustrated) to be rotated in the counterclockwise direction in FIG. 1. When the feeding roller 3 is rotated, the cam 14 (see FIGS. 2A and 2B) disposed coaxially with the feeding roller 3 is rotated in synchronization therewith. As the cam 14 is rotated in synchronization with the rotation of the feeding roller 3, the sheets S stacked on the sheet supporting plate 6 abut on the feeding roller 3, and the sheets S stacked on the sheet supporting plate 6 are fed by the feeding roller 3. Thereafter, only the uppermost sheet S1 among the fed sheets S is separated from the other sheets by the separation roller 5 and conveyed in a downstream direction.
Thereafter, the uppermost sheet S1 separated by one sheet passes through a pair of conveying rollers 16 along a conveyance path 46, and is conveyed to a transfer portion configured of the photosensitive drum 49 a and the transfer roller 49 b through a pair of registration rollers 48. At this time, a toner image visualized by a development device (not illustrated) is formed on the surface of the photosensitive drum 49 a based on a scanning laser beam output from the laser scanner 50. The toner image formed on the photosensitive drum 49 a is transferred onto the conveyed sheet S1 by the transfer roller 49 b in the transfer portion.
In this way, the sheet S1 transferred with the toner image is conveyed in the downstream direction, and the toner image is melt and fixed while being heated and pressed by the fixing device 51. Thereafter, the sheets pass through a pair of conveying rollers 52 and a pair of discharge rollers 53 and are sequentially stacked on the discharge tray 54.

[Sheet Feeding Portion and Sheet Cassette]

FIGS. 2A and 2B are diagrams for describing the configurations of the sheet feeding portion and the sheet cassette 2. FIG. 2A is a diagram illustrating the entire sheet cassette, and FIG. 2B is an enlarged diagram of mechanisms operated by the sheet supporting plate auxiliary member 12 and the cam 14 to be described below.
In FIG. 2A, there are illustrated a sheet cassette case 2A and side regulating plates 7 and 8 which restrict the end positions of the sheet in a direction (hereinafter, referred to as a width direction) perpendicular to the sheet conveying direction. A rear-end regulating plate 9 restricts the rear end position of the sheet. These side regulating plates 7 and 8 and the rear-end regulating plate 9 are provided to slide in the sheet cassette body in order to restrict the positions of end portions of various-sized sheets.
The sheet supporting plate 6 is disposed to be rotated by the rotation center 11 with respect to the sheet cassette case 2A, and receives a pressing force (a pressing force) by the sheet supporting plate spring 10 disposed on the lower surface of the sheet supporting plate 6 as described above with reference to FIG. 1. In addition, on either side of the sheet cassette case 2A, the sheet supporting plate auxiliary member 12 is disposed in each end in the width direction as a restricting portion which is freely rotated about the same rotation center as the rotation center 11 of the sheet supporting plate 6. The sheet supporting plate auxiliary member 12 is formed to restrict the upper surface of the sheet supporting plate 6 having the pressing force by the sheet supporting plate spring 10, and includes a regulating roller 13. The regulating roller 13 is held on the sheet supporting plate auxiliary member 12 to be rotated, and at least two or more regulating rollers are provided in the width direction of the sheet so as to support all types of sheet stacked in the sheet cassette case 2A. In addition, the sheet supporting plate auxiliary member 12 includes a cam follower portion 12 a which abuts on the cam 14 at a position facing the cam 14 disposed coaxially with the driving shaft of the feeding roller 3.
In addition, as described above with reference to FIG. 1, the separation roller 5 and the separation spring 24 which presses the separation roller 5 are integrally disposed in the sheet cassette 2. In other words, when the sheet cassette 2 is drawn out of the apparatus body 1, the sheet supporting plate 6 and the separation roller 5 retract from the feeding roller 3. Therefore, for example, the sheet stuck on a sheet conveyance path can be easily removed.
FIGS. 3A and 3B are diagrams for describing the feeding operation in a state where the sheet cassette is in a full load state of sheets. FIG. 3A illustrates a standby state immediately before a feeding start signal is transmitted. FIG. 3B illustrates a state after the feeding operation starts.
In FIGS. 3A and 3B, the sheet cassette 2 is in the full load state of the sheets S, the sheets S are stacked on the upper surface of the sheet supporting plate 6, and the sheet supporting plate 6 is always pressed from the lower side toward the feeding roller 3 by the sheet supporting plate spring 10. The sheet S is always pressed toward the feeding roller 3 by the pressing force from the sheet supporting plate spring 10 similarly to the sheet supporting plate 6. Herein, a posture of the sheet supporting plate auxiliary member 12 is determined by the regulating roller 13 which abuts on the uppermost sheet S1 by the weight of the sheet supporting plate auxiliary member 12 itself. In other words, the sheet supporting plate auxiliary member 12 receives the pressing force indirectly from the sheet supporting plate spring 10 through the sheet S, and thus is pressed toward the feeding roller 3.
Next, the cam 14 serving as the moving portion will be described. The cam 14 is disposed coaxially with the rotation shaft of the feeding roller 3, and is rotated in synchronization with the rotation of the feeding roller. Herein, the cam follower portion 12 a of the sheet supporting plate auxiliary member 12 is located at a position facing the cam surface of the cam 14, and the rotation of the cam 14 causes the sheet supporting plate auxiliary member 12 to move. The sheet supporting plate auxiliary member 12 is provided to be rotated independently of the sheet supporting plate 6. The regulating roller 13 abuts on the uppermost sheet stacked on the sheet supporting plate 6 by the weight of the sheet supporting plate auxiliary member 12 itself, and the position of the uppermost sheet is restricted to a position separated from the feeding roller 3 through the regulating roller 13. The cam 14 makes the sheet supporting plate auxiliary member 12 rotate to restrict the uppermost sheet S1 stacked on the sheet supporting plate 6 to the position separated from the feeding roller 3. In addition, when the feeding roller 3 feeds the sheet, the cam 14 releases the position of the uppermost sheet S1 restricted by the sheet supporting plate auxiliary member 12 in order to make the uppermost sheet stacked on the sheet supporting plate 6 come in press contact with the feeding roller 3 by the sheet supporting plate spring 10. As described above, since the sheet supporting plate auxiliary member 12 comes into contact with the sheet supporting plate 6 through the sheet S, the rotation of the cam 14 causes the sheet supporting plate 6 to move.

[Feeding Operation of Sheet]

Next, the feeding operation of the sheet will be described. FIG. 3A is a diagram illustrating the standby state before the feeding starts. As illustrated in FIG. 3A, the cam 14 abuts on the cam follower portion 12 a of the sheet supporting plate auxiliary member 12, and stops in a phase where the sheet supporting plate 6 is restricted in a direction of compressing the sheet supporting plate spring 10. In other words, the cam 14 abuts on the uppermost sheet S1 stacked on the sheet supporting plate 6, and comes into contact with the sheet supporting plate auxiliary member 12, so that the sheet supporting plate auxiliary member 12 is positioned to make the position of the uppermost sheet S1 separated from the feeding roller 3. With this configuration, the regulating roller 13 having the sheet supporting plate auxiliary member 12 abuts on the uppermost sheet stacked on the sheet supporting plate 6, and the sheet is retracted (separated) from the feeding roller 3. A distance from the surface of the feeding roller 3 at this time to the uppermost sheet S1 is set to Lf. The position illustrated in FIG. 3A is a position at which the uppermost sheet S1 is separated from the feeding roller 3.
FIG. 3B is a diagram illustrating a state after the feeding operation starts. As illustrated in FIG. 3B, the feeding roller 3 and the cam 14 starts to rotate in a clockwise direction in the drawing and rotatably moves to a phase where the positional restriction of the sheet supporting plate 6 is released, so that the abutting of the cam 14 on the cam follower portion 12 a of the sheet supporting plate auxiliary member 12 is released. In other words, the cam 14 rotatably moves to a position separated from the sheet supporting plate auxiliary member 12. Therefore, the positional restriction of the sheet by the regulating roller 13 of the sheet supporting plate auxiliary member 12 is released. When the sheet supporting plate 6 is released from the restriction by the regulating roller 13 of the sheet supporting plate auxiliary member 12, the uppermost sheet S comes in press contact with the feeding roller 3 by the pressing force of the sheet supporting plate spring 10. At the same time, the sheet receives a conveying force from the feeding roller 3 and fed out, and then conveyed to a separation nip formed by the separation roller 5 and the feeding roller 3. One sheet among the sheets S which reach the separation nip finally is separated by a separation pressure exerted on the separation roller 5 from the separation spring 24, and then conveyed to the subsequent procedure.
Next, the feeding operation in a state where the sheet cassette is in a light load state of the sheets will be described using FIGS. 4A and 4B. FIGS. 4A and 4B are diagrams for describing the feeding operation in a state where the sheet cassette is in the light load state of the sheets. FIG. 4A illustrates the standby state immediately before a signal indicating the feeding start is transmitted. FIG. 4B illustrates a state after the feeding operation starts. Further, the operation is similar to that of the full load state described using FIGS. 3A and 3B, and the detailed description thereof will not be repeated. Herein, a difference between the full load state and the light load state will be described.
Comparing the light load state with the full load state of the sheets, the distance Lf described with reference to FIG. 3A and a distance Le denoted in FIG. 4A are the same. In addition, the relation satisfies Lf=Le. This is because the position of the sheet supporting plate auxiliary member 12 is determined only by the phase where the cam 14 is stopped. In other words, it means that the position of the uppermost sheet S1 on which the regulating roller 13 abuts is not influenced by an amount of the sheets S stacked on the sheet supporting plate 6. In other words, no change of the uppermost position of the sheets S according to the stacked amount means that the position of the sheet supporting plate 6 stacked with the sheets S is changed according to the stacked amount. Further, similarly to FIG. 3A, the position illustrated in FIG. 4A is a position where the uppermost sheet S1 is separated from the feeding roller 3.
Herein, a comparative example of the present example will be described using FIGS. 5A and 5B. In the comparative example, the cam 14 is configured to directly operate the sheet supporting plate 6 as illustrated in FIGS. 5A and 5B. FIG. 5A illustrates a standby position at the time of the full load state of the sheets, and FIG. 5B illustrates a standby position at the time of the light load state of the sheets.
In the comparative example, as illustrated in FIGS. 5A and 5B, the operation of the sheet supporting plate 6 becomes constant regardless of the stacked amount of the sheets S, and a relation of the distance between the feeding roller 3 and the uppermost position of the sheets S becomes Lf<Le. In the comparative example, a moving distance of the sheet supporting plate from the standby state before the feeding operation at the time of the light load state of the sheets until the feeding operation starts, and a time between the operations become large compared to the full load state of the sheets. These increased distance and time cause a collision noise between the sheet supporting plate and the feeding roller at the time of the light load state of the sheets and an increase in operation interval, so that the flexibility of a sequence is degraded.
Unlike the comparative example, according to the example, the cam 14 pushes down the stacked sheets through the sheet supporting plate auxiliary member 12 and thus the sheet supporting plate 6 is operated. With this configuration, it is possible to constantly maintain a distance between the feeding roller and the uppermost position of the sheets regardless of the amount of the sheets stacked in the sheet cassette. Therefore, it is possible to constantly maintain the moving distance of the sheet supporting plate from the standby state before the feeding operation until the feeding operation starts, and a time between the operations regardless of the stacked amount of the sheets. Furthermore, the collision noise generated by a difference in amount of the stacked sheets can be reduced and the varying operation interval can be made to be constant, so that it is possible to contribute greatly to the flexibility of the sequence. In addition, the above effects can be achieved through a simple and inexpensive configuration without requiring a unique driving source.

Second Example

An image forming apparatus which includes the sheet feeding portion serving as a sheet feeding apparatus according to a second example will be described using FIGS. 6A and 6B. The image forming apparatus according to the example has the same configuration as the image forming apparatus described in the first example except the configuration to be described below.
FIGS. 6A and 6B are cross-sectional views illustrating main parts of a sheet feeding portion according to the second example, in which FIG. 6A illustrates the standby state immediately before a signal indicating the feeding start is transmitted. FIG. 6B illustrates the state after the feeding operation starts.

[Sheet Feeding Portion]

The sheets S are stacked in the sheet cassette 2, and the stacked sheets S are disposed on the upper surface (sheet stacking surface) of the sheet supporting plate 6 which is rotatably provided. In a case where a distance of the sheet stacking surface on a side near the feeding roller (on the downstream side in the feeding direction) from the rotation center 11 is set to W and a distance of the sheet stacking surface on a side opposite to the feeding roller is set to Q, the sheet supporting plate 6 is configured to satisfy a relation of W<Q.
With the above configuration, since a barycentric position of the sheet supporting plate 6 is inclined toward the sheet stacking surface of the distance Q from the rotation center 11, the sheet supporting plate 6 is always pressed toward the feeding roller 3 by a rotational inertia force. Similarly, the sheet S is also always pressed toward the feeding roller 3 by the rotational inertia force of the sheet supporting plate 6.
Herein, the sheet supporting plate auxiliary member 12 is disposed to be rotated about the rotation center coaxially with the rotation center 11 of the sheet supporting plate 6, and the posture thereof is determined by the weight of the sheet supporting plate auxiliary member 12 itself. In other words, the sheet supporting plate auxiliary member 12 is provided with the regulating roller 13 such that the regulating roller 13 is rotated by the weight of the sheet supporting plate auxiliary member 12. Further, the regulating roller 13 is held in a state of abutting on the uppermost sheet among the sheets S stacked on the sheet supporting plate 6. In other words, the sheet supporting plate auxiliary member 12 indirectly receives the rotational inertia force from the sheet supporting plate 6 through the sheet S, and pressed toward the feeding roller 3.
Next, the cam 14 will be described. The cam 14 is disposed coaxially with the rotation shaft of the feeding roller 3, and is rotated in synchronization with the rotation of the feeding roller 3. Herein, the sheet supporting plate auxiliary member 12 is located at a position facing the cam surface of the cam 14, and the operation of the cam 14 is transferred to the sheet supporting plate auxiliary member 12. The sheet supporting plate auxiliary member 12 is configured such that the regulating roller 13 abuts on the uppermost sheet stacked on the sheet supporting plate 6 by the weight of the sheet supporting plate auxiliary member 12, and thus restricts the position of the uppermost sheet to a position separated from the feeding roller 3 through the regulating roller 13. The cam 14 rotates (moves) the sheet supporting plate auxiliary member 12 to restrict the uppermost sheet S1 stacked on the sheet supporting plate 6 to the position separated from the feeding roller 3. In addition, when the feeding roller 3 feeds the sheet, the cam 14 releases the restriction on the position of the uppermost sheet S1 by the sheet supporting plate auxiliary member 12 such that the uppermost sheet stacked on the sheet supporting plate 6 comes in press contact with the feeding roller 3 by the sheet supporting plate spring 10. As described above, in order to make the sheet supporting plate auxiliary member 12 abut on the sheet supporting plate 6 through the sheet S, the cam 14 (that is, the sheet supporting plate 6) is operated.
In addition, the cam 14 is connected to the sheet supporting plate 6 by a sheet supporting plate tension spring 15. The sheet supporting plate tension spring 15 is an elastic member to generate the pressing force with which the sheet supporting plate 6 comes in press contact with the feeding roller 3. As described below, the sheet supporting plate tension spring 15 does not generate the pressing force at the position where the uppermost sheet is separated from the feeding roller 3, but generates the pressing force to be large as the uppermost sheet moves from the position separated from the feeding roller 3 until the uppermost sheet comes in press contact with the feeding roller 3.

[Feeding Operation of Sheet]

Next, the feeding operation of the sheet will be described. FIG. 6A is a diagram illustrating the standby state before the feeding start. As illustrated in FIG. 6A, the cam 14 abuts on the cam follower portion 12 a of the sheet supporting plate auxiliary member 12, and stops in a phase where the sheet supporting plate 6 is restricted at a retracting position from the feeding roller 3. In other words, the cam 14 abuts on the uppermost sheet S1 stacked on the sheet supporting plate 6 and comes in contact with the sheet supporting plate auxiliary member 12 such that the sheet supporting plate auxiliary member 12 is located at a position where the position of the uppermost sheet S1 is separated from the feeding roller 3. In this way, the regulating roller 13 of the sheet supporting plate auxiliary member 12 abuts on the uppermost sheet S1 stacked on the sheet supporting plate 6 to retract (separate) the sheet S1 from the feeding roller 3. At this time, the tension spring 15 connected between the cam 14 and the sheet supporting plate 6 is disposed at a position where the spring pressure is not generated. In other words, a force applied to the sheet supporting plate 6 toward the feeding roller 3 in the standby state before the feeding corresponds only to the rotational inertia force of the sheet supporting plate 6. Further, the position illustrated in FIG. 6A is a position where the uppermost sheet S1 is separated from the feeding roller 3.
FIG. 6B is a diagram illustrating a state after the feeding operation starts. As illustrated in FIG. 6B, the feeding roller 3 and the cam 14 start to rotate in a clockwise direction in the drawing, and rotatably move to be a phase where the restriction of the sheet supporting plate 6 is released, so that the abutment of the cam 14 on the cam follower portion 12 a of the sheet supporting plate auxiliary member 12 is released. In other words, the cam 14 rotatably moves to a position separated from the sheet supporting plate auxiliary member 12. With this configuration, the positional restriction of the sheet by the regulating roller 13 of the sheet supporting plate auxiliary member 12 is released. Furthermore, the tension spring 15 connected between the cam 14 and the sheet supporting plate 6 moves up to a position where a spring pressure is generated according to the rotation of the cam 14, and the sheet supporting plate 6 comes in press contact with the feeding roller 3 by the spring pressure of the tension spring 15. In other words, the uppermost sheet S1 stacked on the sheet supporting plate 6 comes in press contact with the feeding roller 3. At the same time, the sheet S1 receives the conveying force from the feeding roller 3, and is conveyed to the separation nip formed by the separation roller 5 and the feeding roller 3. One sheet among the sheets S which reach the separation nip finally is separated by a separation pressure exerted on the separation roller 5 from the separation spring 24, and then conveyed to the subsequent procedure.
With the above configuration, the sheet supporting plate 6 gradually raises the pressing force in a process of abutting on the feeding roller 3 according to the rotation of the cam 14 between a retraction position (see FIG. 6A) where no spring pressure is generated and an abutment position (see FIG. 6B). Therefore, it is possible to suppress a large collision which may occur when the compressed spring is suddenly released.
Further, the description herein has been made about the configuration where the cam 14 and the sheet supporting plate 6 are connected by the tension spring 15 and the spring pressure of the tension spring 15 is not generated at the retraction position illustrated in FIG. 6A, but the invention is not limited thereto. It is no matter that a weak spring pressure is generated at the retraction position as long as the pressing force is configured to gradually rise in the process of abutting on the feeding roller 3 according to the rotation of the cam 14 between the retraction position illustrated in FIG. 6A and the abutment position illustrated in FIG. 6B. Even in such a configuration, it is possible to suppress a large collision generated at the time when the compressed spring is released.
As described above, by employing the configuration of the example, in addition to the effect obtained in the first example, it is possible to more reduce the collision caused in process of making the sheet supporting plate come in press contact with the feeding roller, and the sheet feeding apparatus having a high silence property can be provided.

Third Example

An image forming apparatus which includes a sheet feeding portion serving as a sheet feeding apparatus according to a third example will be described using FIG. 7. The image forming apparatus according to the example has the same configuration as the image forming apparatus described in the second example except the configuration to be described below.
FIG. 7 is a cross-sectional view illustrating main parts of the sheet feeding portion according to the third example, and illustrates a state after the feeding operation starts.
The sheet feeding portion according to the example includes a sheet supporting plate auxiliary spring 25 instead of the above-mentioned configuration of the sheet supporting plate 6 of the second example. The sheet supporting plate auxiliary spring 25 is disposed on the lower side of the sheet supporting plate 6. The sheet supporting plate auxiliary spring 25 is a biasing member which generates a biasing force to always apply a force to the sheet supporting plate 6 toward the feeding roller 3, and is an elastic member having a low pressure compared to the sheet supporting plate tension spring 15. In the state where the sheet supporting plate 6 is in the full load state of with the sheets S, the sheet supporting plate auxiliary spring 25 is set to the lowest value (a possibly low pressure of the spring pressure) of the spring pressure under which the sheet supporting plate 6 is movable toward the feeding roller 3.
According to the example, compared to the above-mentioned second example, it is possible to reduce the collision generated in process of making the sheet supporting plate 6 come in press contact with the feeding roller 3 while applying a force to the sheet supporting plate 6 toward the feeding roller 3 by the biasing force stabilized by the spring pressure, and the sheet feeding apparatus having a high silence property can be provided.

Other Examples

In the above-mentioned example, the description has been made about the sheet feeding apparatus which is integrally provided with the image forming apparatus, but the invention is not limited thereto. For example, the sheet feeding apparatus may be detachably attachable to be optionally connected to the image forming apparatus, and the same effect can be obtained by applying the invention to the sheet feeding apparatus.
In addition, in the above-mentioned example, the description has been made about the sheet feeding apparatus which feeds the sheet such as the recording target sheet, but the invention is not limited thereto. For example, even in a case where the invention is applied to the sheet feeding apparatus which feeds the sheet such as a reading target original, the same effect can be obtained.
In the above-mentioned example, the printer has been exemplified as the image forming apparatus, but the invention is not limited thereto. For example, the invention may be applied to another image forming apparatus such as an image reading apparatus (for example, a scanner), a copying machine, and a facsimile machine, or other image forming apparatuses such as a multifunction peripheral in which these functions are combined. The same effect can be obtained by applying the invention to the image reading apparatuses or to the sheet feeding apparatuses used in the image forming apparatus.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2014-035117, filed Feb. 26, 2014, which is hereby incorporated by reference herein in its entirety.

Claims

What is claimed is:

1. A sheet feeding apparatus comprising:

a stacking member configured to be rotatably provided and to stack a sheet;

a feeding member configured to feed the sheet by being rotated in a state of coming in contact with the sheet stacked on the stacking member;

an elastic member configured to generate a pressing force to make the sheet stacked on the stacking member come in contact with the feeding member; and

a restricting unit configured to abut on an uppermost sheet stacked on the stacking member and to restrict a position of the uppermost sheet to a position separated from the feeding member.

2. The sheet feeding apparatus according to claim 1,

wherein the restricting unit includes

a restricting portion which abuts on the uppermost sheet stacked on the stacking member and restricts a position of the uppermost sheet to the position separated from the feeding member, and

a moving portion which moves the restricting portion to restrict the uppermost sheet stacked on the stacking member to the position separated from the feeding member and releases the positional restriction of the uppermost sheet caused by the restricting portion to make the uppermost sheet stacked on the stacking member come in contact with the feeding member by the elastic member when the feeding member feeds the sheet.

3. The sheet feeding apparatus according to claim 2,

wherein the restricting portion is provided to be rotated independently of the stacking member, and a rotation center of the restricting portion is the same as a rotation center of the stacking member.

4. The sheet feeding apparatus according to claim 2,

wherein the restricting portion includes a regulating roller which is rotatably provided and abuts on the sheet stacked on the stacking member.

5. The sheet feeding apparatus according to claim 2,

wherein the moving portion is provided coaxially with the feeding member, and

wherein the moving portion rotates in synchronization with the feeding member to a position abutting on the restricting portion and to a position separated from the restricting portion in order to make a restricting portion abut on the uppermost sheet stacked on the stacking member and locate the uppermost sheet to the position separated from the feeding member.

6. The sheet feeding apparatus according to claim 4,

wherein the elastic member connects the stacking member and the moving portion, and generates the pressing force to be increased according to the movement from the position separated from the feeding member of the uppermost sheet to the position coming in contact with the feeding member.

7. The sheet feeding apparatus according to claim 6,

wherein the stacking member is configured such that a rotation center is positioned to make the center of gravity inclined in a direction abutting on the feeding member, and is always pressed toward the feeding member by a rotational inertia force.

8. The sheet feeding apparatus according to claim 6,

wherein the stacking member includes a biasing member which generates a biasing force to be always applied to the feeding member, and

wherein the biasing member is an elastic member having a low pressure compared to the elastic member.

9. An image forming apparatus which forms an image in a recording target sheet, comprising:

a sheet feeding apparatus configured to feed the sheet,

wherein the sheet feeding apparatus includes:

a stacking member which is rotatably provided and stacks the sheet;

a feeding member which comes in contact with the sheet stacked on the stacking member and rotates to feed the sheet;

an elastic member which generates a pressing force to make the sheet stacked on the stacking member come in contact with the feeding member; and

a restricting unit which abuts on the uppermost sheet stacked on the stacking member to restrict a position of the uppermost sheet to a position separated from the feeding member.