SHEET FEEDING DEVICE AND IMAGE FORMING APPARATUS

Abstract

One aspect of the present invention provides a sheet feeding device and an image forming apparatus, in which a sheet can stably be separated and fed irrespective of stiffness of the sheet. A movable wall includes a sheet abutting surface that separates the sheet one by one by abutting on the sheet, which is stacked on a tray and fed by a feeding roller. The movable wall is movable in a sheet feeding direction, and a force applying spring applies a force to the movable wall in a direction opposite to the sheet feeding direction. A support portion supports the movable wall such that the movable wall is movable, and such that the movable wall is sloped when abutting on the sheet, which is fed by a feeding roller, and moving on a downstream side in the sheet feeding direction against an applying force of a force applying spring.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeding device and an image forming apparatus, particularly to a sheet feeding device and an image forming apparatus, in which a sheet is separated one by one using a separating slope.

2. Description of the Related Art

Conventionally, an image forming apparatus, such as a copying machine, a printer, and a facsimile machine, includes a sheet feeding device that feeds a sheet to an image forming portion, and a separating portion is provided in the sheet feeding device in order to separate the sheet one by one. For example, there is a separating portion including a slope separation system (see U.S. Pat. No. 5,622,364). In the slope separation system, a separating slope is provided on a leading end side of a tray on which the sheet is stacked, and the sheet fed by a feeding roller is pressed against the separating slope to separate the sheet one by one.

Nowadays, there are various kinds of sheets. Therefore, it is necessary even for the conventional sheet feeding device to feed different sheets having large or small stiffness. For the conventional sheet feeding device including the slope separation system, thick paper having the large stiffness is required to be fed by a large conveying force, in order that the uppermost sheet pressed against the separating slope is conveyed along the separating slope while a leading end of the uppermost sheet is bent upward and separated.

It is conceivable that an angle of the separating slope is decreased such that the uppermost sheet can be conveyed by the small force while separated, namely, such that the force necessary to separate and convey the uppermost sheet is decreased. However, for the decreased angle of the separating slope, a force, which presses the uppermost sheet such that the next sheet is not fed due to a curvature of the uppermost sheet by the slope, is smaller than a frictional force between the sheets in the case that thin paper having the small stiffness is fed. In this case, a ratio that indicates generation of multi feeding is increased because a lower sheet is conveyed together with the uppermost sheet. That is, separating performance degrades for the sheet having the small stiffness when the force necessary to separate and convey the sheet having the large stiffness is decreased, and the force necessary to separate and convey the sheet having the large stiffness increases when the sheet having the small stiffness is securely separated.

It is desirable to provide a sheet feeding device and an image forming apparatus, in which the sheet can stably be separated and fed irrespective of the stiffness of the sheet in the slope separation system.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a sheet feeding device includes: a sheet stacking portion on which a sheet is stacked; a sheet feeding portion which feeds the sheet stacked on the sheet stacking portion; a separating portion which includes a separating slope, the separating slope separating the sheet one by one by abutting on the sheet fed by the sheet feeding portion, the separating slope being movable along a sheet feeding direction; a force applying portion which applies a force to the separating portion in a direction opposite to the sheet feeding direction; and a support portion which supports the separating portion such that the separating portion is movable, and such that the separating portion is sloped in connection with the movement when abutting on the sheet fed by the sheet feeding portion and moving a downstream side in the sheet feeding direction against an applying force of the force applying portion.

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 view illustrating a configuration of an image forming apparatus including a sheet feeding device according to a first embodiment of the present invention;

FIG. 2 is a view illustrating a configuration of a separating portion provided in the sheet feeding device;

FIGS. 3A and 3B are views illustrating movement of a movable wall constituting the separating portion;

FIGS. 4A and 4B are schematic diagrams illustrating a force applied to the movable wall;

FIG. 5 is a view illustrating a relationship between an acting force of a force applying spring, which applies a force to the movable wall, and a conveying force according to a type of sheet;

FIG. 6 is a view illustrating a conveying force of a feeding roller;

FIGS. 7A, 7B, and 7C are views illustrating a sheet feeding operation of the sheet feeding device;

FIG. 8 is a view illustrating a relationship between a slope angle of the movable wall and the conveying force;

FIG. 9 is a first view illustrating a configuration of a separating portion provided in a sheet feeding device according to a second embodiment of the present invention;

FIG. 10 is a second view illustrating the configuration of the separating portion; and

FIGS. 11A, 11B, and 11C are views illustrating a sheet feeding operation of the sheet feeding device.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a view illustrating a configuration of an image forming apparatus including a sheet feeding device according to a first embodiment of the present invention. In FIG. 1, the numeral 50 designates a laser beam printer and the numeral 50A designates a laser beam printer body (hereinafter referred to as a printer body). The printer body 50A includes an image forming portion 50B. A sheet feeding device 1 that feeds a sheet S, such as a recording sheet, which is stacked on and stored in a tray 3, to the image forming portion 50B is provided in a lower portion of the printer body 50A.

The image forming portion 50B includes a process cartridge 21, and the process cartridge 21 includes a photosensitive drum 21a, a charging device (not illustrated), a development sleeve (not illustrated), and a cleaner (not illustrated). The image forming portion 50B also includes a laser scanner 20 that exposes a surface of the photosensitive drum 21a to form an electrostatic latent image on the photosensitive drum 21a. The printer body 50A includes a transfer roller 21b and a fixing portion 22. The transfer roller 21b abuts on the photosensitive drum 21a, and constitutes a transfer portion together with the photosensitive drum 21a. The fixing portion 22 fixes a toner image, which is transferred by the transfer portion, onto a sheet S.

The sheet feeding device 1 includes a feeding roller 5 and a separating portion 30. The feeding roller 5 that is of the sheet feeding portion feeds the sheet S, which is stacked on the tray 3 that is of the sheet stacking portion on which the sheet S is stacked, from the uppermost side. The separating portion 30 separates the sheet one by one. The feeding roller 5 is turnably supported by a turning end part of a turning arm 17. The turning arm 17 is supported while being vertically turnable about a turning shaft 4 that is retained by a stay (not illustrated) fixed to a sheet feeding device body (not illustrated). Irrespective of a stacking level of the sheet S stacked on the tray 3, the feeding roller 5 abuts on an upper surface of an uppermost sheet Sa by the turn of the turning arm 17. In the first embodiment, in setting the sheet S on the tray 3, the sheet S is pushed into the tray 3 from a lateral side (a right side of the printer body in FIG. 1) of the printer body 50A.

An image forming operation of the laser beam printer 50 having the above configuration will be described below. When the image forming operation is started, the photosensitive drum 21a rotates clockwise, the surface of the photosensitive drum 21a is charged by the charging device (not illustrated), and the laser scanner 20 emits a laser beam to the photosensitive drum 21a based on image information. Therefore, the electrostatic latent image is formed on the photosensitive drum. Then the electrostatic latent image is developed using toner, and visualized as the toner image.

On the other hand, in parallel with the toner image forming operation, the feeding roller 5 of the sheet feeding device 1 rotates while abutting on the uppermost sheet Sa on the tray 3, thereby feeding the uppermost sheet Sa. After the uppermost sheet Sa fed by the feeding roller 5 is conveyed by the separating portion 30 while separated one by one, the uppermost sheet Sa is conveyed to the transfer portion by a conveying roller pair 23, and the image on the photosensitive drum 21a is transferred to the uppermost sheet Sa by the transfer roller 21b. Then, the uppermost sheet Sa to which the toner image is transferred is conveyed to the fixing portion 22, and unfixed toner image is heated and pressurized by passing between a heating roller 22a and a pressure roller 22b, thereby fixing the toner image to the surface of the sheet. A sheet Sa, to which the toner image is already fixed, is discharged on a discharge tray 27 by a discharge roller 26 while the image surface of the sheet Sa is oriented downward.

FIG. 2 is a view illustrating a configuration of the separating portion 30. Referring to FIG. 2, the separating portion 30 includes a movable wall 6, support members 31 and 32 that movably support the movable wall 6, a fixed wall 33, a force applying spring 10 that is of a compression spring provided between the movable wall 6 and the fixed wall 33, and a cam 7. A sheet abutting surface 6b that is of the separating slope is provided on the feeding roller side of the movable wall 6. The sheet abutting surface 6b includes a slope. The sheet S fed by the feeding roller 5 is pressed against the slope, and the slope is inclined with respect to a vertical direction in which the sheet is conveyed while separated one by one. Two bosses (projections) 6a are projected in each of side surfaces in a width direction, which is orthogonal to the sheet feeding direction, of the movable wall 6 that is of the separating portion movable along the sheet feeding direction. The two bosses 6a are disposed along the sheet feeding direction in order to determine a moving direction of the movable wall 6 or an attitude of the movable wall 6 during the movement.

First and second boss grooves 9a and 9b, in which the bosses 6a of the movable wall 6 are movable, are formed in each of the support members 31 and 32 that are of the support portion movably supporting the movable wall 6. The support members 31 and 32 movably support the movable wall 6 with the first and second boss grooves 9a and 9b interposed therebetween. In the first embodiment, the first boss groove 9a located on the side of the sheet abutting surface 6b of the movable wall 6 is formed in substantially parallel with a sheet stacking surface 3a of the tray 3 in FIG. 1. The second boss groove 9b located on a downstream side of the boss groove 9a in the sheet feeding direction is formed sloped such that the downstream side of the second boss groove 9b in the sheet feeding direction is lowered.

As illustrated in FIG. 3A, the movable wall 6 is usually maintained in a standby state in which the bosses 6a of the movable wall 6 abut on upstream ends of the first and second boss grooves 9a and 9b in the sheet feeding direction by the force applying spring 10 provided between the movable wall 6 and the fixed wall 33. The sheet abuts on the movable wall 6 in setting the sheet on the tray, whereby a spring force of the force applying spring 10 that is of the force applying portion applying the force to the movable wall 6 in the direction opposite to the sheet feeding direction is set to magnitude at which the movable wall 6 does not move even if an external force Fx is applied. Therefore, the movable wall 6 is maintained in the standby state in FIG. 3A, when the external force Fx is not applied or when the external force Fx is smaller than a force applying spring acting force Fsp obtained by the applying force of the force applying spring 10.

When the external force Fx is larger than the force applying spring acting force Fsp of the force applying spring 10, the movable wall 6 moves onto the downstream side in the sheet feeding direction while the bosses 6a move along the first and second boss grooves 9a and 9b as illustrated in FIG. 3B. At this point, when the bosses 6a move, the movable wall 6 is guided by the first and second boss groove 9a and 9b described above that is of the guide portion such that the movable wall 6 moves onto the downstream side in the sheet feeding direction while sloped. Therefore, an angle formed between the sheet abutting surface 6b of the movable wall 6 and the sheet stacking surface 3a of the tray 3 changes. The fed sheet moves the movable wall 6 against the applying force of the force applying spring 10, and the movable wall 6 moves onto the downstream side in the sheet feeding direction from the standby position in FIG. 3A to the state in FIG. 3B, whereby the angle (a slope angle) between the sheet abutting surface 6b and the sheet stacking surface 3a changes from θ1 to θ2. That is, the acute angle between the sheet abutting surface 6b and the sheet stacking surface 3a decreases (θ1→θ2).

The cam 7 regulates the movement of the movable wall 6 on the downstream side in the sheet feeding direction, and the cam 7 abuts on the surface on the opposite side to the sheet abutting surface 6b of the movable wall 6 to regulate the movement of the movable wall 6 until the feeding roller 5 starts to feed the sheet. In feeding the sheet, while the feeding roller 5 rotates, a signal is input to a solenoid (not illustrated) from an electric board (not illustrated) to attract the solenoid, and a driving force is transmitted from a driving train (not illustrated) to rotate the cam 7. The rotation of the cam 7 that is of the regulation portion releases the regulation of the cam 7. Therefore, the movable wall 6 can move onto the downstream side in the sheet feeding direction when the sheet fed by the feeding roller 5 abuts on the movable wall 6.

FIG. 4 is a schematic diagram illustrating forces acting onto the movable wall 6, FIG. 4A is a schematic diagram illustrating the forces acting onto the movable wall 6 in the first embodiment, and FIG. 4B is a reference drawing for comparison. In FIG. 4B, a movable wall 206 turns with a turning center 206a as a supporting point. The turning center 206a is provided below the sheet stacking surface 3a. For the movable wall 206, because of a short distance (R2) between the turning center 206a and the sheet abutting surface 206b of the movable wall 206, force applying spring acting forces Fsp1, Fsp2, and Fsp3 of the force applying spring 10 are largely different depending on the position in a height direction of the sheet abutting surface 206b.

Therefore, even if external forces Fx1, Fx2, and Fx3 are equal to one another, namely, even if forces are equal to one another when the sheet fed by the feeding roller 5 abuts on the movable wall 206, the movable wall 206 easily moves in the case that external force Fx1 acts on the upper side of the sheet abutting surface 6b. The movable wall 6 hardly moves in the case that external force Fx3 acts on the lower side of the sheet abutting surface 6b.

On the other hand, in the case that the bosses 6a and the first and second boss groove 9a and 9b guide the movement of the movable wall 6 like the first embodiment, the turning center of the movable wall 6 can be located downward far away from the sheet stacking surface 3a compared with the case in FIG. 4B. In this case, because of a long distance (R1) between the turning center and the sheet abutting surface 6b of the movable wall 6, the difference among the force applying spring acting forces Fsp1, Fsp2, and Fsp3 of the force applying spring 10 can be reduced irrespective of the position in the height direction of the sheet abutting surface 6b. Therefore, a fluctuation in external force depending on the position in the height direction of the external force (the forces Fx1, Fx2, and Fx3 are equal to one another), which is of a condition that the movable wall 6 moves, namely, the fluctuation in external force depending on the stacking level of the sheet S is reduced to stably separate the sheet S.

FIG. 5 is a view illustrating a relationship between the force applying spring acting force Fsp of the force applying spring 10 and the conveying force of the sheet S according to a type of sheet. In FIG. 5, a vertical axis indicates conveying forces Fz of typical sheet S in a situation in which the movable wall 6 is fixed to the position in the standby state, namely, the forces, which are generated by the difference in stiffness of the sheet and are necessary to convey the sheet S with the leading end bent. The vertical axis also indicates a conveying force Fr obtained from the feeding roller 5 and the force applying spring acting force Fsp of the force applying spring 10.

The conveying force Fr of the feeding roller 5 will be described with reference to FIG. 6. The conveying force Fr of the feeding roller 5 is obtained by multiplying a normal reaction N, which is generated by the rotation and bite of the feeding roller 5, by a friction factor between the feeding roller 5 and the sheet S. The normal reaction N is determined by conditions such as a distance h between the turning shaft 4 and the uppermost sheet Sa and a distance L between the turning shaft 4 and the feeding roller 5. The distance h changes according to the stacking level of the sheet S. The friction factor between the feeding roller 5 and the sheet S is determined by conditions such as a material for the feeding roller 5 and the type of the sheet S.

In the first embodiment, the surface of the sheet abutting surface 6b is set such that the conveying forces Fz for the thin paper (basis weight of 60 g/m²) and the plain paper (basis weight of 80 g/m²) are less than or equal to about 3 N, and such that the conveying forces Fz for the thick paper (basis weight of 160 g/m²) and an envelope are greater than or equal to about 10 N. At this point, the conveying force Fr obtained from the feeding roller 5 is substantially kept constant even if the distance h changes. In setting the conveying force Fr to a given value, the force applying spring acting force Fsp of the force applying spring 10 is set so as to be greater than the conveying forces Fz for the plain paper and the thin paper and so as to be less than the conveying forces Fz for the thick paper and the envelope and the conveying force Fr of the feeding roller 5. Therefore, in the first embodiment, the force applying spring acting force Fsp of the force applying spring 10 is set to 5 N in order to satisfy the above conditions.

A sheet feeding operation of the sheet feeding device 1 will be described below with reference to FIG. 7. FIG. 7A illustrates the state when a user sets the sheet S into the tray 3. At this point, the cam 7 is located at a home position to abut on the surface on the opposite side to the sheet abutting surface 6b of the movable wall 6, whereby the movement of the movable wall 6 is regulated. When the user sets the sheet S into the tray 3, the movable wall 6 does not move even if the sheet S abuts on the movable wall 6. Therefore, the user can easily set the sheet S by abutting the leading end of the sheet S on the movable wall 6. That is, a good setting property can be provided in setting the sheet S.

FIG. 7B illustrates the state in which the thin paper having the basis weight of 60 g/m² is fed. In the case that the sheet is fed, the signal is input to the solenoid from the electric board (not illustrated) to start the rotation of the cam 7, the cam 7 separates from surface on the opposite side to the sheet abutting surface 6b of the movable wall 6, and the movable wall 6 is put into the movable state.

When the feeding roller 5 starts the rotation to feed the uppermost sheet Sa abutting on the feeding roller 5, the uppermost sheet Sa is pressed against the sheet abutting surface 6b of the movable wall 6 to which the applying force is applied by the force applying spring 10. At this point, although the conveying force Fr of the feeding roller 5 is applied to the movable wall 6, the conveying force Fr necessary to convey the uppermost sheet Sa with the leading end bent is smaller than the force applying spring acting force Fsp of the force applying spring 10 because the uppermost sheet Sa is the thin paper. Therefore, the movable wall 6 does not move.

When the uppermost sheet Sa is further pressed against the sheet abutting surface 6b of the movable wall 6 while the movable wall 6 does not move, the uppermost sheet Sa is fed while only the leading end of the uppermost sheet Sa is bent. Therefore, the uppermost sheet Sa separates from the lower sheet, and the uppermost sheet Sa is conveyed to the conveying roller pair 23 while guided by the sheet abutting surface 6b of the movable wall 6.

At this point, in the lower sheet, the conveying force Fr of the feeding roller 5 is insufficient because the conveying force Fr acts on the lower sheet via the frictional force between the sheets. Even if the leading end of the lower sheet abuts on the sheet abutting surface 6b of the movable wall 6, the leading end is not bent and the lower sheet is not conveyed. Therefore, the lower sheet is not fed together with the uppermost sheet Sa, and the multi feeding is not generated. After the uppermost sheet Sa is conveyed to the conveying roller pair 23, the cam 7 again reaches the home position at which the cam 7 abuts on the surface on the opposite side to the sheet abutting surface 6b of the movable wall 6, and the cam 7 stops the rotation.

FIG. 7C illustrates the state in which the thick paper having the basis weight of 160 g/m² is fed. In this case, the uppermost sheet Sa is conveyed by the rotation of the feeding roller 5, and pressed against the sheet abutting surface 6b of the movable wall 6 to which the force is applied by the force applying spring 10. At this point, although the conveying force Fr of the feeding roller 5 is applied to the movable wall 6, the conveying force Fr has predetermined stiffness or more because the sheet is the thick paper. Therefore, the conveying force Fr is larger than the force applying spring acting force Fsp of the force applying spring 10, which is necessary to convey the uppermost sheet Sa with the leading end bent.

Accordingly, the uppermost sheet Sa presses the movable wall 6 without bending the leading end, and the movable wall 6 moves along the first and second boss grooves 9a and 9b. The movement of the movable wall 6 decreases the slope angle θ formed between the sheet abutting surface 6b and the sheet stacking surface 3a.

FIG. 8 illustrates a relationship between the conveying force Fz and the slope angle θ in feeding the thick paper having the basis weight of 160 g/m². As can be seen from FIG. 8, the conveying force Fz necessary to convey the sheet S with the leading end bent decreases with decreasing slope angle θ. In FIG. 8, when the slope angle Γ reaches about 72°, the movement of the movable wall 6 is stopped by the applying force of the force applying spring 10 to bend the leading end of the uppermost sheet Sa. Then, the uppermost sheet Sa is conveyed to the conveying roller pair 23 while guided by the sheet abutting surface 6b and the guide.

At this point, in the lower sheet, the conveying force Fr of the feeding roller 5 is insufficient because the conveying force Fr acts on the lower sheet via the frictional force between the sheets, but the leading end of the lower sheet cannot be bent and conveyed even if the leading end of the lower sheet abuts on the sheet abutting surface 6b. Therefore, the lower sheet is not fed together with the uppermost sheet Sa, and the multi feeding is not generated. After the uppermost sheet Sa is conveyed to the conveying roller pair 23, the cam 7 again reaches the home position at which the cam 7 abuts on the surface on the opposite side to the sheet abutting surface 6b of the movable wall 6, and the cam 7 stops the rotation.

As described above, in the first embodiment, the movable wall 6 is movably provided, and the movable wall 6 is sloped by the movement. Therefore, a wide variety of sheets from the thin paper that is of the sheet having weak conveying force to the thick paper or envelope that is of the sheet having the strong conveying force can surely be separated and fed. The turning center of the movable wall 6 is largely separated below the sheet stacking surface 3a, so that the change in force applying spring acting force Fsp of the force applying spring 10 acting on the uppermost sheet Sa can be decreased even if the stacking level of the sheet S changes. As a result, the fluctuation of the condition that the movable wall 6 moves according to the stacking level of the sheet S can be decreased and the stable sheet separating and feeding performance can be exerted.

In the first embodiment, the movable wall 6 having the sheet abutting surface 6b is sloped when the sheet fed by the feeding roller 5 abuts on the movable wall 6 to move the movable wall 6. Therefore, the sheet can stably be separated and fed irrespective of the stiffness of the sheet.

As described above, in the first embodiment, the good setting property can be provided by providing the cam 7 when the user sets the sheet into the tray. The stable sheet separating and feeding performance can also be exerted even in the case that the cam 7 is not provided.

A second embodiment of the present invention will be described below. FIGS. 9 and 10 are views illustrating a configuration of a sheet feeding device according to a second embodiment. In FIGS. 9 and 10, the component identical or equivalent to that in FIGS. 2 and 3 is designated by the identical numeral.

In the second embodiment, as illustrated in FIGS. 9 and 10, the first boss groove 9a is formed so as to be inclined obliquely upward with increasing distance from the feeding roller 5. In the case that the first boss groove 9a in FIGS. 9 and 10 is formed, the angle formed between the sheet abutting surface 6b of the movable wall 6 and the sheet stacking surface 3a changes when the movable wall 6 moves, and the upper end of the sheet abutting surface 6b is always higher than a height H6 at the position in the standby state irrespective of a movement amount of the movable wall 6.

FIG. 11A illustrates the state in which the user sets the sheet S into the tray 3 in the second embodiment. At this point, the cam 7 abuts on the surface on the opposite side to the sheet abutting surface 6b of the movable wall 6. FIG. 11B illustrates the state in which the thin paper having the basis weight of 60 g/m² is fed. At this point, the cam 7 separates from the movable wall 6, and the movable wall 6 is in the movable state.

When the feeding roller 5 starts the rotation to feed the uppermost sheet Sa, the uppermost sheet Sa is pressed against the sheet abutting surface 6b of the movable wall 6 to which the applying force is applied by the force applying spring 10. At this point, the movable wall 6 is in the movable state, and the conveying force Fr of the feeding roller 5 is applied to the movable wall 6 via the uppermost sheet Sa. However, the conveying force Fr necessary to convey the sheet S with the leading end bent is smaller than the force applying spring acting force Fsp of the force applying spring 10 because the uppermost sheet Sa is the thin paper. Therefore, the movable wall 6 does not move.

When the uppermost sheet Sa is further pressed against the sheet abutting surface 6b of the movable wall 6 while the movable wall 6 does not move, the uppermost sheet Sa is fed while only the leading end of the uppermost sheet Sa is bent, thereby separating the uppermost sheet Sa from the lower sheet. The separated uppermost sheet Sa is conveyed to the conveying roller pair 23 while guided by the sheet abutting surface 6b of the movable wall 6.

At this point, in the lower sheet, the conveying force Fr of the feeding roller 5 is small because the conveying force Fr acts on the lower sheet via the frictional force between the sheets. Even if the leading end of the lower sheet abuts on the sheet abutting surface 6b of the movable wall 6, the leading end is not bent and the lower sheet is not conveyed. Therefore, the lower sheet is not fed together with the uppermost sheet Sa, and the multi feeding is not generated. After the uppermost sheet Sa is conveyed to the conveying roller pair 23, the cam 7 again reaches the home position at which the cam 7 abuts on the surface on the opposite side to the sheet abutting surface 6b of the movable wall 6, and the cam 7 stops the rotation.

FIG. 11C illustrates the state in which the thick paper having the basis weight of 160 g/m² is fed. At this point, the cam 7 separates from the movable wall 6, and the movable wall 6 is in the movable state. When the feeding roller 5 starts the rotation to feed the uppermost sheet Sa, the uppermost sheet Sa is pressed against the sheet abutting surface 6b of the movable wall 6 to which the force is applied by the force applying spring 10. At this point, the movable wall 6 is in the movable state, and the conveying force Fr of the feeding roller 5 is applied to the movable wall 6. However, the conveying force Fr necessary to convey the uppermost sheet Sa with the leading end bent is larger than the force applying spring acting force Fsp of the force applying spring 10 because the uppermost sheet Sa is the thick paper. Therefore, the movable wall 6 moves along the first and second boss grooves 9a and 9b.

When the movable wall 6 moves, the slope angle θ formed between the sheet abutting surface 6b and the sheet stacking surface 3a changes according to the movement amount. The relationship between the slope angle θ and the conveying force Fz for the thick paper having the basis weight of about 160 g/m² is illustrated in FIG. 8 described above, and the second embodiment conforms to the relationship in FIG. 8. Referring to FIG. 8, the leading end of the uppermost sheet Sa is bent when the slope angle θ reaches about 72°, and then the uppermost sheet Sa is conveyed to the conveying roller pair 23 while guided by the sheet abutting surface 6b and a guide on the downstream side.

At this point, in the lower sheet, the conveying force Fr of the feeding roller 5 is small because the conveying force Fr acts on the lower sheet via the frictional force between the sheets, but the leading end of the lower sheet cannot be bent and conveyed even if the leading end of the lower sheet abuts on the sheet abutting surface 6b. Therefore, the lower sheet is not fed together with the uppermost sheet Sa, and the multi feeding is not generated. After the uppermost sheet Sa is conveyed to the conveying roller pair 23, the cam 7 again reaches the home position at which the cam 7 abuts on the surface on the opposite side to the sheet abutting surface 6b of the movable wall 6, and the cam 7 stops the rotation.

In the case that the first boss groove 9a is formed in substantially parallel to the sheet stacking surface 3a, when the movable wall 6 is sloped by the movement, the level at the upper end of the sheet abutting surface 6b of the movable wall 6 is lowered compared with the height H6 at the position in the standby state as the movable wall 6 moves as illustrated in FIG. 7. On the other hand, in the second embodiment, the first boss groove 9a is formed so as to be inclined obliquely upward with increasing distance from the feeding roller 5. In the second embodiment, when the movable wall 6 is sloped by the movement, the level at the upper end of the sheet abutting surface 6b of the movable wall 6 is not lower than the height H6 at the position in the pre-slope standby state.

Therefore, the leading end of the uppermost sheet Sa can surely be guided to a given level by the sheet abutting surface 6b of the movable wall 6 irrespective of the movement amount of the movable wall 6, and the sheet can be fed without generating a conveying failure in a gap with the guide on the downstream side or a step.

As described above, in the second embodiment, the first boss groove 9a is formed so as to be inclined obliquely upward with increasing distance from the feeding roller 5. Therefore, while the performance of stably separating and feeding the sheet with the sheet pressed against the sheet abutting surface 6b of the movable wall 6 is maintained, the sheet can surely be fed even if the movable wall 6 moves.

In the configuration of the second embodiment, the upper end of the sheet abutting surface 6b is always the height H6 at the position in the standby state irrespective of a movement amount of the movable wall 6. However, the second embodiment is not limited to this, and depending on a shape of the boss groove 9a, the upper end of the sheet abutting surface 6b may be higher than the height H6 at the position in the standby state as the movable wall 6 moves. Even in this case, the leading end of the uppermost sheet Sa can surely be guided to the given level or more by the sheet abutting surface 6b of the movable wall 6 even if the movable wall 6 moves.

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 modifications, equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2012-263766, filed Nov. 30, 2012, which is hereby incorporated by reference herein in its entirety.

Claims

1. A sheet feeding device comprising:

a sheet stacking portion on which a sheet is stacked;

a sheet feeding portion which feeds the sheet stacked on the sheet stacking portion;

a separating portion which includes a separating slope, the separating slope separating the sheet one by one by abutting on the sheet fed by the sheet feeding portion, the separating portion being movable along a sheet feeding direction;

a force applying portion which applies a force to the separating portion in a direction opposite to the sheet feeding direction; and

a support portion which supports the separating portion such that the separating portion is movable, and such that the separating portion is sloped in connection with the movement when abutting on the sheet, which is fed by the sheet feeding portion, and moving on a downstream side in the sheet feeding direction against an applying force of the force applying portion.

2. The sheet feeding device according to claim 1, wherein the support portion includes a guide portion which guides the separating portion when the separating portion moves onto the downstream side in the sheet feeding direction while sloped.

3. The sheet feeding device according to claim 2, wherein the guide portion is formed such that an upper end position of the separating slope is higher than a level of the pre-slope upper end position when the separating portion is sloped.

4. The sheet feeding device according to claim 1, wherein the applying force of the force applying portion is set to magnitude at which the separating portion moves when the sheet having predetermined stiffness or more abuts on the separating portion.

5. The sheet feeding device according to claim 1, wherein the support portion includes a projection and a groove, the projection guiding the separating portion when the separating portion moves onto the downstream side in the sheet feeding direction while sloped, the projection being guided in the groove,

a pair of the projection and the groove is disposed on each of both sides of the separating portion along the sheet feeding direction, and

when the separating portion moves on the downstream side in the sheet feeding direction, the groove disposed on an upstream side substantially horizontally or upwardly guides the projection and the groove disposed on the downstream side downwardly guides the projection.

6. The sheet feeding device according to claim 1, further comprising a regulation portion which abuts on the separating portion to regulate the movement of the separating portion on the downstream side in the sheet feeding direction until the sheet feeding portion starts to feed the sheet.

7. An image forming apparatus comprising:

a sheet feeding device including:

a sheet stacking portion on which a sheet is stacked;

a sheet feeding portion which feeds the sheet stacked on the sheet stacking portion;

a separating portion which includes a separating slope, the separating slope separating the sheet one by one by abutting on the sheet fed by the sheet feeding portion, the separating portion being movable along a sheet feeding direction;

a force applying portion which applies a force to the separating portion in a direction opposite to the sheet feeding direction; and

a support portion which supports the separating portion such that the separating portion is movable, and such that the separating portion is sloped in connection with the movement when abutting on the sheet, which is fed by the sheet feeding portion, and moving on a downstream side in the sheet feeding direction against the applying force of the force applying portion, and

an image forming portion which forms an image on the sheet fed from the sheet feeding device.

8. The image forming apparatus according to claim 7, wherein the support portion includes a guide portion which guides the separating portion when the separating portion moves onto the downstream side in the sheet feeding direction while sloped.

9. The image forming apparatus according to claim 8, wherein the guide portion is formed such that an upper end position of the separating slope is higher than a level of the pre-slope upper end position when the separating portion is sloped.

10. The image forming apparatus according to claim 7, wherein the applying force of the force applying portion is set to magnitude at which the separating portion moves when the sheet having predetermined stiffness or more abuts on the separating portion.

11. The image forming apparatus according to claim 7, wherein the support portion includes a projection and a groove, the projection guiding the separating portion when the separating portion moves onto the downstream side in the sheet feeding direction while sloped, the projection being guided in the groove,

a pair of the projection and the groove is disposed on each of both sides of the separating portion along the sheet feeding direction, and

when the separating portion moves on the downstream side in the sheet feeding direction, the groove disposed on an upstream side substantially horizontally or upwardly guides the projection and the groove disposed on the downstream side downwardly guides the projection.

12. The image forming apparatus according to claim 7, further comprising a regulation portion which abuts on the separating portion to regulate the movement of the separating portion on the downstream side in the sheet feeding direction until the sheet feeding portion starts to feed the sheet.