Sheet-feed separation mechanism, sheet feeding device, image reading device, and image forming apparatus

Abstract

A sheet feeding device that draws out a sheet from a pile of sheets, including: a sheet tray on which the pile of sheets is placed; a sheet feeding roller whose peripheral surface is pressed to abut on a top surface of an uppermost sheet in the pile of the sheets at a downstream end in a sheet feeding direction of the pile of sheets; a friction pad disposed oppositely to the sheet feeding roller to form a nip portion for the sheet with the sheet feeding roller; and a pushing member that pushes the friction pad in a direction opposite to the sheet feeding direction.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet-feed separation mechanism and a sheet feeding device that feed sheets one by one separately from a pile of sheets, and an image forming apparatus to which these are applied.

2. Description of the Related Art

Conventionally, a sheet-feed separation mechanism, such as those disclosed in JP-A-4-354740 (Reference 1) and JP-A-2005-67784 (Reference 2), has been known.

The sheet-feed separation mechanism of Reference 1 is provided correspondingly to a sheet feeding container (sheet tray) in an image forming apparatus, such as a copying machine and a facsimile machine, and it draws out sheets one by one from a pile of sheets stored in the sheet tray and feeds them toward the image forming apparatus. This sheet-feed separation mechanism is formed of a sheet feeding roller that is provided at the downstream end in a sheet carrying direction in the sheet tray and driven to rotate about the central axis thereof, and a friction pad that abuts on the peripheral surface of the sheet feeding roller at the lower portion of the sheet feeding roller. The sheet feeding roller and the friction pad are made of materials having large coefficients of friction, such as rubber. The friction pad presses the peripheral surface of the sheet feeding roller with a pushing force of the spring.

In a pile of sheets stored in the sheet tray, the uppermost sheet is pushed upward by specific pushing means while the top surface thereof abuts on the lower peripheral surface of the sheet feeding roller and the edge of the top surface at a downstream side of the sheet is stopped by abutting on the friction pad. By rotationally driving the sheet feeding roller in this state, the uppermost sheet is pulled out from the sheet tray as it is guided by the peripheral surface of the sheet feeding roller having a large coefficient of friction, and fed to the inside of the image forming apparatus.

With the sheet-feed separation mechanism configured as above, in a case where, for example, two sheets are pulled out from the sheet tray in association with the driven rotations of the sheet feeding roller, these two sheets are brought in a state where they are nipped between the peripheral surface of the sheet feeding roller that is driven-rotating and the top surface of the friction pad. In this state, the frictional force between the uppermost sheet and the second sheet is not only smaller than the frictional force between the uppermost sheet and the peripheral surface of the sheet feeding roller, but is also smaller than the frictional force between the second sheet and the top surface of the friction pad. Hence, the uppermost sheet is pulled out by the sheet feeding roller whereas the second sheet will not be pulled out as it is interfered with by the friction pad. It is thus possible to prevent an event that two sheets are fed at a time, that is, so-called two-sheet feeding.

The sheet-feed separation mechanism of Reference 2 is provided to the document tray of a copying machine, a facsimile machine, or the like, and it draws out documents one by one from a pile of documents that is formed of plural stacked documents and placed on the document tray, and feeds them to the document reading portion.

Basically, as with the one disclosed in Reference 1, this separation mechanism is formed of a sheet feeding roller provided at the end of the document tray on the document reading portion side and driven to rotate about the central axis thereof, and a friction pad that abuts on the peripheral surface of the sheet feeding roller at the lower portion of the sheet feeding roller. The two-sheet feeding of the documents is prevented by the same function as that of Reference 1. However, in contrast to Reference 1 where the friction pad is not allowed to oscillate, the friction pad is attached to the pad holder configured to be able to oscillate in the top-bottom direction.

Reference 2 describes that it is possible to suppress vibrations of a document by allowing the friction pad to oscillate while the document is fed, which can in turn eliminate so-called fluttering sounds produced when the document vibrates finely while being fed.

Both the sheet-feed separation mechanisms of Reference 1 and Reference 2, however, have a problem that the two-sheet feeding occurs in some cases under a circumstance that the uppermost sheet and the second sheet are not separated easily because each sheet is not readily peeled at the edge in the pile of sheets depending on the kinds of sheet or the cut finishing.

SUMMARY OF THE INVENTION

An advantage of the invention is to provide a sheet-feed separation mechanism and a sheet feeding device capable of preventing two-sheet feeding in a reliable manner, and an image reading device or an image forming apparatus to which these are applied.

A sheet-feed separation mechanism according to one aspect of the invention that achieves the above advantage includes: a sheet feeding roller that draws out a sheet; a friction pad disposed oppositely to the sheet feeding roller to form a nip portion for the sheet with the sheet feeding roller; and a pushing member that pushes the friction pad in a direction opposite to the sheet feeding direction.

A sheet feeding device according to another aspect of the invention is a sheet feeding device that draws out a sheet from a pile of sheets, including: a sheet tray on which the pile of sheets is placed; a sheet feeding roller whose peripheral surface is pressed to abut on a top surface of an uppermost sheet in the pile of the sheets at a downstream end in a sheet feeding direction of the pile of sheets; a friction pad disposed oppositely to the sheet feeding roller to form a nip portion for the sheet with the sheet feeding roller; and a pushing member that pushes the friction pad in a direction opposite to the sheet feeding direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are sectional side views of a printer to which a sheet-feed separation mechanism according to one embodiment of the invention is applied, FIG. 1A showing a state where a sheet cassette is accommodated at an accommodation position and FIG. 1B showing a state where the sheet cassette is pulled out to a pull-out position.

FIG. 2 is a perspective view showing one embodiment of a sheet feeding device.

FIG. 3 is an exploded perspective view showing one embodiment of the sheet-feed separation mechanism.

FIG. 4 is an assembly perspective view of the sheet-feed separation mechanism shown in FIG. 3.

FIGS. 5A and 5B are cross sections taken on line V-V of FIG. 4, FIG. 5A showing a state where a friction pad is located at a home position and FIG. 5B showing a state where the friction pad is located at a pushing force conferring position.

FIGS. 6A through 6E are explanatory views to describe the function of the sheet-feed separation mechanism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A and 1B are explanatory views when viewed in a cross-sectional transverse plane schematically showing the inner structure of one example of a printer 10 to which one embodiment of a sheet-feed separation mechanism of the invention is applied. FIG. 1A shows a state where a sheet cassette 31 is accommodated at an accommodation position T1, and FIG. 1B shows a state where the sheet cassette 31 is pulled out to a pull-out position T2. In FIGS. 1A and 1B, the Y-Y direction is defined as the front-back direction, and in particular, the −Y direction is defined as the front and the +Y direction as the rear.

The printer 10 includes a sheet feeding device 30 configured to store sheets P1 used for print processing and to draw out sheets P1 one by one from a stored pile of sheets P1 (a pile of sheets, P) or to feed a sheet P1 manually. The printer 10 further includes an image forming portion 20 that applies transfer processing of an image to a sheet P1 fed from the sheet feeding device 30, a fixing portion 27 that applies fixing processing to a sheet P1 done with the transfer processing in the image forming portion 20, both of which are installed inside an apparatus main body 11 at a position above a partition wall 115. A sheet P1 done with the fixing processing in the fixing portion 27 is discharged onto a sheet discharge tray 117 formed on top of the apparatus main body 11.

The sheet feeding device 30 (sheet feeding device or first sheet feeding device as claimed) is formed of a sheet cassette 31 attached to the apparatus main body 11 in a reattachable manner for storing the pile of sheets, P, and a manual sheet feeding portion 38 provided at a front end portion of the sheet cassette 31. The apparatus main body 11 is provided with a sheet feeding roller 311 having a large diameter for drawing out the sheets P1 one by one from the top in the pile of sheets, P, at a position corresponding to the upstream end (front side) of the sheet cassette 31, and a carrying roller 312 having a small diameter at a position directly above the sheet feeding roller 311.

A sheet P1 drawn out from the sheet cassette 31 by the driving of the sheet feeding roller 311 is fed to the image forming portion 20 via the carrying roller 312 by passing through a sheet-feed carrying path 313 and a pair of register rollers 314 provided at the downstream end thereof. The sheet cassette 31 will be described again below in reference to FIG. 2.

The image forming portion 20 is to apply the transfer processing to a sheet P1 according to image information transmitted from a computer or the like. The image forming portion 20 is formed of a photoconductive drum 21 provided in a rotatable manner about the central axis thereof extending in the right-left direction (a direction perpendicular to the sheet surface of FIG. 1), plus a charger 22, an exposing device 23, a developing device 24, a transfer roller 25, and a cleaning device 26, which are disposed sequentially in a clockwise direction from the position directly above the photoconductive drum 21 to go along the peripheral surface thereof.

The photoconductive drum 21 is to form an electrostatic latent image and a toner image corresponding to the electrostatic latent image on the peripheral surface thereof. An amorphous silicon layer suitable to form an electrostatic latent image and a toner image is layered on the peripheral surface of the photoconductive drum 21.

The charger 22 is to form charges uniformly on the peripheral surface of the photoconductive drum 21 that is rotating about the central axis thereof in a clockwise direction. In this embodiment, it adopts the corona discharge method, by which charges are conferred to the peripheral surface of the photoconductive drum 21 by means of corona discharge from the wire. Instead of this method, the charging roller method may be adopted, by which charges are conferred to the peripheral surface of the photoconductive drum 21 while being driven rotated with its peripheral surface abutting on the peripheral surface of the photoconductive drum 21.

The exposing device 23 irradiates a laser beam having differences in intensity according to the image data sent from an outside device, such as a computer, to the peripheral surface of the photoconductive drum 21 that is rotating. Charges are erased from a portion where a laser beam was irradiated, and an electrostatic latent image is consequently formed on the peripheral surface of the photoconductive drum 21.

The developing device 24 is to form a toner image on the peripheral surface of the photoconductive drum 21 by supplying toner particles contained in the developing agent to the peripheral surface of the photoconductive drum 21 for the toner particles to adhere onto the peripheral surface in a portion where the electrostatic latent image has been formed. As the developing agent, for example, those based on a two-component made of toner and a carrier can be adopted. As the toner particles, fine powder having a particle size of 6 to 12 μm and formed by dispersing a coloring agent, a charge control agent, and additive agents, such as wax, into binder resin can be adopted. As the carrier, magnetic particles having a particle size of 60 to 200 μm, such as magnetite (Fe₃O₄), can be adopted.

The transfer roller 25 transfers a toner image formed on the peripheral surface of the photoconductive drum 21 and charged positively onto a sheet P1 sent to a position directly below the photoconductive drum 21. The transfer roller 25 confers negative charges of the polarity opposite to that of the charges of the toner image to the sheet P1.

A sheet P1 having reached the position directly below the photoconductive drum 21 undergoes the transfer processing while being pressed and nipped by the transfer roller 25 and the photoconductive drum 21. The transfer processing is the processing to strip the toner image on the peripheral surface of the photoconductive drum 21 toward the surface of the negatively charged sheet P1.

The cleaning device 26 is to clean the photoconductive drum 21 after the transfer processing to the sheet P1 by removing toner remaining on the peripheral surface thereof. The peripheral surface of the photoconductive drum 21 cleaned by the cleaning device 26 heads for the charger 22 again for the following image forming processing.

The fixing portion 27 applies fixing processing by heating to a toner image on the sheet P1 done with the transfer processing in the image forming portion 20. The fixing portion 27 includes a heat roller 271 to which a current-carrying heat generator, such as a halogen lamp, is attached in the inside, and a pressure roller 272 disposed below the heat roller 271 in such a manner that their peripheral surfaces oppose each other. A sheet P1 done with the transfer processing undergoes fixing processing by receiving heat from the heat roller 271 as it passes by the nip portion between the heat roller 271 that is driven to rotate about the central axis thereof in a clockwise direction and the pressure roller 272 that is driven rotated about the central axis thereof in a counter-clockwise direction. The sheet P1 done with the fixing processing is discharged onto the sheet discharge tray 117 by passing through a sheet discharging and carrying path 273.

The manual feeding portion 38 includes a front wall 381 and a manual tray 382 supported on the front wall 381. The front wall 381 is used as a guide plane that guides a sheet P1 from the sheet feeding roller 311 to the image forming portion 20.

Hereinafter, the sheet feeding device 30 will be described in detail in reference to FIG. 2. FIG. 2 is a perspective view showing one embodiment of the sheet feeding device 30. In FIG. 2, the X-X direction is defined as the right-left direction and the Y-Y direction is defined as the front-back direction. In particular, the −X direction is defined as the left, the +X direction as the right, the −Y direction as the front, and the +Y direction as the rear.

The sheet feeding device 30 includes the sheet cassette 31 and the manual sheet feeding portion 38 formed at the front end position of the sheet cassette 31. The sheet cassette 31 is formed of an arc-shaped front plate 32 whose front surface is provided to swell outwards (frontward) in an arc shape when viewed in a plane, a bottom plate 33 provided to extend backward from the lower edge of the arc-shaped front plate 32 on the back surface (rear surface) side, and a pair of side plates 34 provided to stand upward from the both sides on the right and the left of the bottom plate 33 and extending in the front-back direction, and it exhibits a rectangular box shape with an open top surface when viewed in a plane.

A pair of guided protruding pieces 341 protruding in directions opposite to each other is provided to each side plate 34 at an appropriate portion. Meanwhile, a pair of side plates 111 (FIG. 1B) of the apparatus main body 11 is provided with recesses that define guide grooves 111a extending in the front-back direction and corresponding to the guided protruding pieces 341. The sheet cassette 31 is allowed to change the positions between an accommodation position T1 (FIG. 1A) at which it is accommodated in the apparatus main body 11 and a pull-out position T2 (FIG. 1B) at which it protrudes to the outside from the apparatus main body 11, as the respective guided protruding pieces 341 move in forward and reverse directions by being guided by these guide grooves 111a.

The bottom plate 33 is provided with a front-back movement guiding concave portion 331 that extends in the front-back direction on the top surface side at the center position in the right-left direction, and a front-back position limiting member 35 that is allowed to move in the front-back direction by being guided by the front-back movement guiding concave portion 331. The limiting member 35 is to limit the position of the rear end of the pile of sheets, P (FIGS. 1A and 1B), placed on the bottom plate 33, and has a horizontal plate 351 that slides inside the front-back movement guiding concave portion 331 and a vertical plate 352 provided to stand up from the rear end portion of the horizontal plate 351. The vertical plate 352 is moved to match the sheet size and stopped by abutting on the rear end of the pile of sheets, P.

In addition, the bottom plate 33 is provided with a crosswise pair of right-left movement guiding concave portions 332 at the front position of the top surface, and a pair of right/left position limiting members 36 that are allowed to move in the right-left direction by being guided these right-left movement guiding concave portions 332. These limiting members 36 are to limit the right and left positions of the pile of sheets, P, placed on the bottom plate 33, and have horizontal plates 361 that slide inside the corresponding guiding concave portions 332 and vertical plates 362 provided to stand up from the edge portions of the corresponding horizontal plates 361 on the opposite sides in the right-left direction. By moving these limiting members 36 by the same quantity in the opposite directions to match the sheet size, it is possible to pinch the pile of sheets, P, between the pair of vertical plates 362.

The pile of sheets, P, placed on the bottom plate 33 of the sheet cassette 31 is thus positioned inside the sheet cassette 31 with the front end being stopped by abutting on the front wall 381 by being pinched by the front-back position limiting member 35 and the pair of right/left position limiting members 36.

At the front half position of the bottom plate 33, a pushing plate 37 is provided, which pushes upward the front half of the pile of sheets, P, placed in a state not to interfere with the right/left position limiting members 36. The pushing plate 37 is axially supported on a supporting shaft 371 (FIGS. 1A and 1B) extending in the right-left direction at the rear end so as to be able to rotate about the supporting shaft 371, and it is pushed upward by a coil spring 372.

This configuration allows the uppermost sheet P1 in the pile of sheets, P, loaded in the sheet cassette 31 to abut on the sheet feeding roller 311 in a state where the sheet cassette 31 is accommodated inside the apparatus main body 11 (FIG. 1A). Accordingly, the sheets P1 in the pile of sheets, P, are successively sent out toward the image forming portion 20 from the top in association with the driven rotations of the sheet feeding roller 311 via the sheet feeding roller 311, the carrying roller 312, the sheet-feed carrying path 313, and the pair of register rollers 314.

In the sheet feeding device 30 configured as described above, a sheet-feed separation mechanism 40 of the invention is provided to the front wall 381. Hereinafter, the sheet-feed separation mechanism 40 will be described in reference to FIG. 3 through FIG. 5B. FIG. 3 is an exploded perspective view showing one embodiment of the sheet-feed separation mechanism 40, and FIG. 4 is an assembly perspective view. FIGS. 5A and 5B are cross sections of the sheet-feed separation mechanism 40 taken on line V-V of FIG. 4. FIG. 5A shows a state where a friction pad 70 is located at a home position S1, and FIG. 5B shows a state where the friction pad 70 is located at a pushing force conferring position S2. The directions indicated using X and Y in FIG. 3 through FIG. 5B are defined in the same manner as FIG. 2, and X is defined as the right-left direction (−X: left, +X: right) and Y is defined as the front-back direction (−Y: front, +Y: rear).

As is shown in FIG. 3, the sheet-feed separation mechanism 40 is formed of a pedestal member (seat) 50 fit in the front wall 381 of the manual feeding portion 38 (FIG. 2) at the center position in the right-left direction, a pad supporting movable member (pad holder) 60 attached to the pedestal member 50 so as to be movable in forward and reverse directions with respect to the sheet carrying direction, a friction pad 70 attached to the pad supporting movable member 60, and a coil spring 80 that pushes the pad supporting movable member 60 so as to be pressed toward the downstream end in the sheet carrying direction.

When viewed in a side plane corresponding to the rear surface of the front wall 381, the pedestal member 50 is set in a shape that the top half is bent forward. The pedestal member 50 is formed of a crosswise pair of legs 51, and a pad holding member 52 bridged between the upper edge portions of the pair of legs 51 and inclined forward by about 30° with respect to a direction along which the legs 51 extend.

The pad holding member 52 is set to a position at which the surface thereof opposes the peripheral surface of the sheet feeding roller 311 while the sheet cassette 31 is positioned at the accommodation position T1 (FIG. 1A). The pad holding member 52 includes a surface plate 53 whose main surface side is inclined upward toward the front, an almost vertical back surface plate 54 disposed oppositely to the surface plate 53 at the front, a crosswise pair of side plates 55 each provided to bridge between the back surface plate 54 and the front surface plate 53 on their respective edges, a top plate 56 provided to bridge between the back surface plate 54 and the front surface plate 53 on their respective upper edge portions, and a bottom surface is an open state. Each leg 51 is provided to extend downward from the lower portion at the rear end of each side plate 55.

The surface plate 53 is provided with a rectangular attachment concave portion 531 formed by providing a recess in almost the entire surface for the pad supporting movable member 60 to be attached thereto. The recessed quantity of the attachment concave portion 531 is set so that the depth across the surface is slightly larger than the top-bottom dimension of the pad supporting movable member 60. This configuration prevents the pad supporting movable member 60 from protruding to the outside from the attachment concave portion 531 when attached to the inside of the attachment concave portion 531. A bottom surface plate 532 of the attachment concave portion 531 formed in this manner is parallel to the surface plate 53.

The bottom surface plate 532 is provided with a connecting opening 533 that crosses the bottom surface plate 532 in the width direction at the center position in the right-left direction. The connecting opening 533 is provided to transmit a pushing force of the coil spring 80 attached to the back surface of the bottom surface plate 532 to the pad supporting movable member 60. Also, the bottom surface plate 532 is provided with a crosswise pair of guide rails 534 that swell toward the front surface and extend in the width direction of the bottom surface plate 532. These guide rails 534 are to guide movements of the pad supporting movable member 60 inside the attachment concave portion 531.

The attachment concave portion 531 is set in such a manner that the top-bottom width dimension is almost twice as large as the width dimension of the pad supporting movable member 60, and the right-left dimension is slightly larger than the right-left dimension of the pad supporting movable member 60. This configuration allows the pad supporting movable member 60 to move in forward and reverse direction in the inclined direction by sliding on the bottom surface plate 532 inside the attachment concave portion 531 by a quantity almost comparable to its own width dimension.

The pedestal member 50 configured in this manner has supporting point shafts 57 provided to protrude in the opposite directions at positions in close proximity to the legs 51 at the lower portion of the side plates 55, and is supported on the front wall 381 (FIG. 2) so as to be able to rotate about the supporting point shafts 57. Also, the upper portion of the back surface plate 54 is pressed backward by a pushing force of a pressing spring 58. Accordingly, the pedestal member 50 receives a pressing force heading to a counter-clockwise direction about the supporting point shafts 57 from the pressing spring 58, and the friction pad 70 is pressed and stopped by abutting on the peripheral surface of the sheet feeding roller 311.

The pad supporting movable member 60 is to support the friction pad 70, and in this embodiment, it is formed by press processing to bend a pair of side edge portions of a long metal plate of a rectangular shape in the same direction. The pad supporting movable member 60 formed in this manner includes a bottom plate 61 whose dimension is set in such a manner that the length dimension in the right-left direction is slightly smaller than the inner dimension in the right-left direction of the attachment concave portion 531, and a pair of side plates 62 provided to protrude upward from the both side edge portions of the bottom plate 61 and extending in the right-left direction. The height dimension of each side plate 62 is set to be slightly smaller than the recessed quantity of the attachment concave portion 531.

In the pad supporting movable member 60 configured in this manner, the bottom plate 61 is provided with a pair of guided slits 611 made by means of punching whose position and dimension are set in such manner that they externally fit to the pair of the guide rails 534 provided to the bottom surface plate 532 of the pedestal member 50 in a sliding contact state. As the pad supporting movable member 60 is attached to the attachment concave portion 531, the pair of guided grooves 611 fit to the corresponding guide rails 534. This allows the pad supporting movable member 60 to move in forward and reverse directions in the width direction of the attachment concave portion 531 in a stable state where each guided groove 611 is guided by the corresponding guide rail 534.

Also, in the pad supporting movable member 60 configured in this manner, the side plate 62 on the rear is provided with a protruding piece 621 provided to protrude downward from the center position in the right-left direction. In this embodiment, the protruding piece 621 is formed by carving up the bottom plate 61 downward.

The protruding piece 621 is to support the base end (lower portion) of the coil spring 80. In order to ensure this supporting, a circular cylindrical piece 622 whose diameter dimension is slightly smaller than the minor diameter dimension of the coil spring 80 is provided to the protruding piece 621 on the front surface side so as to protrude forward. By externally fitting the base end side of the coil spring 80 to the circular column piece 622, the coil spring 80 is prevented from falling off from the protruding piece 621.

The friction pad 70 is provided to prevent two-sheet feeding of sheets P1 by forming a nip portion with the sheet feeding roller 311 and by nipping a sheet P1 therein. The friction pad 70 is set in such a manner that the length dimension is almost equal to the length dimension of the pad supporting movable member 60, the width dimension is slightly larger than the inner dimension between the pair of side plates 62 of the pad supporting movable members 60, and the thickness dimension is slightly larger than the top-bottom dimension of the side plate 62 of the pad supporting movable member 60.

The friction pad 70 is fit in a space between the pair of side plates 62 while it undergoes compressive elastic deformation in the width direction. When attached to the pad supporting movable member 60, the friction pad 70 is inhibited from falling off from the pad supporting movable member 60 by its own elasticity, and the main surface side protrudes upward from the upper edge portion of the respective side plates 62. As the pad supporting movable member 60 is attached to the attachment concave portion 531 in this state, the top surface of the friction pad 70 slightly protrudes to the outside from the attachment concave portion 531.

The friction pad 70 is made of an elastomer, such as rubber and a soft synthetic resin material, and it confers an adequate frictional force to a sheet P1 while the sheet P1 is nipped between the sheet feeding roller 311 and the friction pad 70. The material of the friction pad 70 is chosen so that the frictional force developed between the friction pad 70 and the sheet P1 becomes smaller than the frictional force developed between the sheet feeding roller 311 and the sheet P1. This configuration allows the sheet P1 nipped between the sheet feeding roller 311 and the friction pad 70 to be drawn out from the pile of sheets, P, in association with the rotations of the sheet feeding roller 311 as the sheet feeding roller 311 rotates about the central axis thereof.

As the material of the friction pad 70, for example, urethane cork-rubber can be used. For the sheet feeding roller 311, EPDM (Ethylene propylene dienmonomer) can be used. Besides the foregoing, various kinds of elastomer can be adopted as long as it satisfies the condition that a frictional force developed with the sheet P1 is smaller with the friction pad 70 than with the sheet feeding roller 311.

The coil spring 80 is to confer a pushing force to the pad supporting movable member 60 to locate the friction pad 70 at the home position S1 via the pad supporting movable member 60. As is shown in FIGS. 5A and 5B, with this coil spring 80, one end portion in a compressed state externally fits to the circular column piece 622 provided to the protruding piece 621 of the pad supporting movable member 60, while the other end portion is stopped by abutting on the corner defined by the back surface plate 54 and the top plate 56 in the pad holding portion 52 of the pedestal member 50.

When the friction pad 70 is located at the home position S1 as is shown in FIG. 5A, the pushing force of the coil spring 80 is smaller than the frictional force between the sheet P1 and the friction pad 70. On the other hand, when the friction pad 70 is in a state where it has moved to the pushing force conferring position S2 as is shown in FIG. 5B, the pushing force of the coil spring 80 is larger than the frictional force between the sheet P1 and the friction pad 70.

While the sheet feeding roller 311 is at rest, the friction pad 70 is pressed backward by the pushing force of the coil spring 80 via the pad supporting movable member 60. The friction pad 70 is thus located at the home position S1 as is shown in FIG. 5A.

On the contrary, when the sheet feeding roller 311 is driven and starts to be driven to rotate about the central axis thereof in a counter-clockwise direction while the uppermost sheet P1 in the pile of sheets, P, abuts on the peripheral surface of the sheet feeding roller 311, as is shown in FIG. 5B, the uppermost sheet P1 is guided by rotations of the sheet feeding roller 311 and pulled out from the pile of sheets, P. Subsequently, the sheet P1 passes by the nip portion N between the peripheral surface of the sheet feeding roller 311 and the top surface of the friction pad 70.

In this instance, the friction pad 70 moves obliquely upward toward the front while compressing the coil spring 80 against the pushing force of the coil spring 80, which gives rise to a state where the frictional force and the pushing force act against each other. The friction pad 70 therefore ceases to move and is located at the pushing force conferring position S2 (FIG. 5B) to confer the pushing force of the coil spring 80 to the sheet P1.

The sheet P1 is drawn out from the pile of sheets, P1 in this state. When the drawing out of the uppermost sheet P1 in the pile of sheets, P, is completed, the friction pad 70 returns to the home position S1 shown in FIG. 5A, and is used to draw out the following sheet P1.

Hereinafter, the function of the sheet-feed separation mechanism 40 will be described more in detail in reference to FIGS. 6A through 6E. FIG. 6A and FIG. 6B show a function of the sheet-feed separation mechanism 40 with time when only a single sheet P1 at the top is drawn out from the pile of sheets, P. FIG. 6C through FIG. 6E show a function of the sheet-feed separation mechanism 40 with time in the case of so-called two-sheet drawing by which two sheets P1, the uppermost sheet P1 and the second sheet P1, are drawn out at a time from the pile of sheets, P. Indications of the direction using Y in FIGS. 6A through 6E are the same as those in FIG. 2 (−Y: front, +Y: rear).

Initially, the pedestal member 50 is pushed by the pushing force of the pressing spring 58 about the supporting point shafts 57 in a counter-clockwise direction and the friction pad 70 is pressed against the peripheral surface of the sheet feeding roller 311, which produces the nip portion N between the friction pad 70 and the sheet feeding roller 311 to nip a sheet P1.

As the sheet feeding roller 311 is driven to rotate about the central axis thereof in a counter-clockwise direction in this state (a state where the friction pad 70 is located at the home position S1), the uppermost sheet P1 in the pile of the sheets, P, pushed upward by the pushing plate 37 is drawn out forward as is shown in FIG. 6A and the tip end of the sheets P1 reaches the nip portion N. At a point in time at which the sheet P1 has reached the nip portion N, the friction pad 70 stays at the home position S1.

Because the driven rotations of the sheet feeding roller 311 are continued at this point in time, the sheet P1 is kept guided by the rotations of the sheet feeding roller 311 and thereby moves forward. In this instance, the friction pad 70 is guided by the movement of the sheet P1 and moves obliquely upward toward the front inside the attachment concave portion 531 against the pushing force of the coil spring 80, and is thereby located at the pushing force conferring position S2 as is shown in FIG. 6B.

In a state located at the pushing force conferring position S2, the friction pad 70 tries to push the sheet P1 positioned in the nip portion N backward using the pushing force of the coil spring 80 having undergone compressive elastic deformation. However, because the frictional force between the friction pad 70 and the sheet P1 is smaller than the frictional force between the sheet feeding roller 311 and the sheet P1, the sheet P1 is pulled forward in association with the rotations of the sheet feeding roller 311 without being pushed back by the friction pad 70.

When the drawing out processing of the uppermost sheet P1 from the pile of sheets, P, is completed and the driven rotations of the sheet feeding roller 311 are suspended to prepare for the drawing out of the following sheet P1, the friction pad 70 is returned to the home position S1 from the pushing force conferring position S2 by the pushing force of the coil spring 80. By driving and suspending the sheet feeding roller 311 repetitively, it is possible to feed the sheets P1 one by one from the pile of sheets, P, toward the image forming portion 20.

The function of the friction pad 70 when two sheets P1 are drawn out at a time from the pile of sheets, P, in association with the driven rotations of the sheet feeding roller 311 will now be described in reference to FIG. 6C through FIG. 6E. In a case where two sheets P1 are drawn out at a time from the pile of sheets, P, in association with driven rotations of the sheet feeding roller 311, as is shown in FIG. 6C, two sheets P1 (hereinafter, the uppermost sheet P1 is referred to as the uppermost sheet P11 and the second sheet P1 as the following sheet P12) reach the nip portion N at the same time.

In this state, as the driven rotations of the sheet feeding roller 311 are continued, the friction pad 70 is guided by the two sheets P1 that rotate in association with the sheet feeding roller 311, and, as is shown in FIG. 6D, is moved once to the pushing force conferring position S2. In this instance, static friction is acting between the uppermost sheet P11 and the following sheet P12.

However, because the frictional force between the uppermost sheet P11 and the sheet feeding roller 311 is larger than the frictional force between the uppermost sheet P11 and the following sheet P12 and the pushing force of the coil spring 80 heading backward is conferred to the following sheet P12 via the friction pad 70 owing to the frictional force between the friction pad 70 and the following sheet P12, sliding occurs between the uppermost sheet P11 and the following sheet P12. This gives rise to dynamical friction between the uppermost sheet P11 and the following sheet P12.

Because the dynamical friction is smaller than the static friction, the friction pad 70 is no longer able to stay at the pushing force conferring position S2 against the pushing force of the coil spring 80. Accordingly, under the circumstances that the uppermost sheet P11 is guided by the sheet feeding roller 311 and kept drawn out forward, as is shown in FIG. 6E, the friction pad 70 is moved toward the home position S1 together with the following sheet P12 by the pushing force of the coil spring 80.

As has been described, even when two sheets P1 are drawn out at a time from the pile of sheets, P, in association with driven rotations of the sheet feeding roller 311, as is shown in FIG. 6E, the friction pad 70, on which the following sheet P12 is abutting, pushes the following sheet P12 backward by the pushing force of the coil spring 80. It is thus possible to prevent reliably two sheets P1 from being fed at a time toward the image forming portion 20 by the sheet feeding roller 311.

Besides a case where two sheets P1 are drawn out at a time, in a case where three or more sheets P1 are drawn out at a time, it is also possible to prevent reliably more than one sheet P1 from being fed to the image forming portion 20 by the function of the friction pad 70 to which the pushing force is conferred from the coil spring 80 in the same manner as above.

As has been described in detail, the sheet-feed separation mechanism 40 of this embodiment includes the sheet feeding roller 311 whose peripheral surface is pressed to abut on the top surface of the uppermost sheet P1 at the downstream end of the pile of sheets, P, placed on the pushing plate 37 in the sheet cassette 31, and the friction pad 70 disposed oppositely to the sheet feeding roller 311 at the lower portion via the uppermost sheet P1. The friction pad 70 is pushed in a direction opposite to the sheet carrying direction by the pushing force of the coil spring 80.

Hence, even when more than one sheet is drawn out at a time from the pile of sheets, P, the uppermost sheet P1 is fed by being guided by the driven rotations of the sheet feeding roller 311 whereas the second sheet P1 is pushed backward in association with the friction pad 70 that was shifted once to the pushing force conferring position S2 from the home position S1 and is now returned to the home position S1 by the pushing force of the coil spring 80. It is thus possible to prevent reliably the occurrence of an inconvenience that more than one sheet P1 is fed to the image forming portion 20 at a time.

A frictional force or the like between the sheets varies with the kind of the sheets P1, and so does a force needed to appropriately draw out the sheet P1. In this embodiment, however, the friction pad 70 moves to a position corresponding to the frictional force between the sheets. Hence, the friction pad 70 moves to the appropriate position that can act against the frictional force between the sheets whenever two sheets are drawn out regardless of the kind of sheets. The friction pad 70 is then pushed back by the coil sprig 80 together with the second sheet alone. In short, the invention is applicable to a pile of sheets having a different peeling force between the sheets. It is therefore possible to prevent reliably the occurrence of an inconvenience that a defect (that is, two-sheet feeding) occurs in the drawing out of a sheet P1 depending on the kind of the sheet P1.

In addition, when the sheet P1 fed from the pile of sheets, P, moves during the driven rotations of the sheet feeding roller 311 while being nipped between the sheet feeding roller 311 and the friction pad 70, vibrations resulting from frictional sliding of the sheet P1 on the friction pad 70 are absorbed by expansion and contraction of the coil spring 80. It is thus possible to prevent reliably the occurrence of so-called fluttering sound produced as the sheet P1 trembles due to the vibrations.

In the embodiment above, the pad supporting movable member 60 that supports the friction pad 70 with the top portion being exposed is provided, and the pedestal member 50 that holds the pad supporting movable member 60 to be able to move in the sheet carrying direction is also provided. The friction pad 70 is therefore attached to the pedestal member 50 in a movable manner via the pad supporting movable member 60 in a stable state.

The accommodation concave portion that accommodates the pad supporting movable member 60 in a movable manner is provided by making a recess in the top surface of the pedestal member 50. This configuration stabilizes the attachment state of the friction pad 70 to the pedestal member 50.

It should be appreciated that the invention is not limited to the embodiment above and includes the contents as follows.

(1) In the foregoing embodiment, the printer 10 is described as an example of the image forming apparatus to which the sheet-feed separation mechanism 40 is applied. The invention, however, is also applicable to a copying machine and a facsimile machine, and further to a scanner or the like that reads a document image and transmits the image information to another device, such as a computer. In a case where the image forming apparatus is a copying machine, a document feeding device (second sheet feeding device) that feeds documents, from which image information is read, is provided as the sheet feeding device of the invention in addition to the sheet cassette 31 (first sheet feeding device). When the image forming apparatus is the scanner i.e. an image reading device, the sheet cassette 31 is omitted, and the document feeding device that feeds a document to an image reading portion provided in a body of the image reading device alone is provided. Incidentally, when the image forming apparatus is the scanner, tailoring the image information read from the document so as to be transmitted to an outside device, such as a computer, is included in the concept of the image formation of the invention.

(2) In the foregoing embodiment, the sheet cassette 31 for storing a transfer sheet with which the transferring processing of an image is performed is described as an example of the sheet feeding device to which the sheet-feed separation device 40 is applied. However, in a case where the image forming apparatus is a copying machine or a facsimile machine, a so-called document feeding tray that feeds the documents toward the image reading portion provided in the apparatus body may be used.

(3) In the foregoing embodiment, the coil spring 80 is described as an example of the pushing member that confers a pushing force to the friction pad 70 via the pad supporting movable member 60. Instead of this member, a plate spring or an elastomer, such as rubber, may be used depending on the situations. In a case where the pushing member is made of rubber or the like, for example, a rubber piece in the shape of a strip, a round rod, or a tube is prepared, and one end of such a rubber piece is attached to the protruding piece 621 while the other end is fixed to the back surface plate 54 or the top plate 56. Even with the use of such a pushing member, it is possible to confer an adequate pushing force to the pad supporting movable member 60 owing to the elasticity of the rubber piece.

(4) In the foregoing embodiment, the pushing force of the coil spring 80 is made smaller than the frictional force between the sheet P1 and the friction pad 70 in a state where the friction pad 70 is at the home position S1. Instead of this configuration, it may be configured in such a manner that the pushing force of the coil spring 80 is made slightly larger than the frictional force with the friction pad 70 in a state where it is located at the home position S1, so that the friction pad 70 stays at the home position S1 during normal sheet feeding, and moves to the pushing force conferring position S2 only when a special sheet (sheet having a large coefficient of friction) is fed.

(5) In the foregoing embodiment, the pad supporting movable member 60 is formed by bending the metal plate. However, instead of such a metal plate, a resin molded article may be used.

The specific embodiment described above includes inventions having the following configurations.

A sheet-feed separation mechanism according to one aspect of the invention includes: a sheet feeding roller that draws out a sheet; a friction pad disposed oppositely to the sheet feeding roller to form a nip portion for the sheet with the sheet feeding roller; and a pushing member that pushes the friction pad in a direction opposite to the sheet feeding direction.

A sheet feeding device according to another aspect of the invention is a sheet feeding device that draws out a sheet from a pile of sheets, including: a sheet tray on which the pile of sheets is placed; a sheet feeding roller whose peripheral surface is pressed to abut on a top surface of an uppermost sheet in the pile of the sheets at a downstream end in a sheet feeding direction of the pile of sheets; a friction pad disposed oppositely to the sheet feeding roller to form a nip portion for the sheet with the sheet feeding roller; and a pushing member that pushes the friction pad in a direction opposite to the sheet feeding direction.

An image reading device according to yet another aspect of the invention includes: a device body having an image reading portion; and a document feeding device that feeds a document sheet from which image information is read to the image reading portion, wherein the document feeding device includes: a sheet tray on which a pile of the document sheet is placed; a sheet feeding roller whose peripheral surface is pressed to abut on a top surface of an uppermost sheet in the pile at a downstream end in a sheet feeding direction of the pile; a friction pad disposed oppositely to the sheet feeding roller to form a nip portion for the sheet with the sheet feeding roller; and a pushing member that pushes the friction pad in a direction opposite to the sheet feeding direction.

An image forming apparatus according to still another aspect of the invention is an image forming apparatus that forms an image according to image information, including a first sheet feeding device that feeds a transfer sheet, and/or a second sheet feeding device that feeds a document sheet from which the image information is read, wherein one or both of the first sheet feeding device and the second sheet feeding device include: a sheet tray on which a pile of the transfer sheet or the document sheet is placed; a sheet feeding roller whose peripheral surface is pressed to abut on a top surface of an uppermost sheet in the pile at a downstream end in a sheet feeding direction of the pile; a friction pad disposed oppositely to the sheet feeding roller to form a nip portion for the sheet with the sheet feeding roller; and a pushing member that pushes the friction pad in a direction opposite to the sheet feeding direction.

According to these configurations, even when more than one sheet is drawn out at a time from a pile of sheets, the second sheet is pushed backward by the friction pad to which the pushing force is conferred while the uppermost sheet in the pile of sheets is being fed by the sheet feeding roller. Moreover, because the friction pad moves in response to a frictional force between the sheets, it can be applied to a pile of sheets of any kind having a different peeling force between the sheets. It is thus possible to prevent reliably an inconvenience that more than one sheet is fed toward the sheet-feed destination at a time regardless of the kinds of sheets.

In addition, when a sheet drawn out from the pile of sheets moves in association with the driven rotations of the sheet feeding roller while being nipped between the sheet feeding roller and the friction pad, vibrations resulting from frictional sliding between the sheet and the friction pad are absorbed by the pushing member. It is thus possible to prevent reliably the occurrence of so-called fluttering sounds produced when the sheet trembles due to vibrations.

In the configuration described above, it is preferable to further include a pad holder that supports the friction pad with a top portion being exposed, and a seat that holds the pad holder in a manner so as to be able to move in forward and reverse directions with respect to the sheet feeding direction. According to this configuration, it is possible to attach the friction pad to the seat in a movable manner via the pad supporting movable member in a stable state.

In this case, it is preferable that an accommodation concave portion to accommodate the pad holder in a movable manner is provided by making a recess in a top surface of the seat. According to this configuration, the attachment state of the friction pad to the seat can be stabilized.

In the configuration described above, the pushing member can be one of a coil spring, a plate spring, and an elastomer. According to this configuration, it is possible to choose the pushing member that best suits the situation.

This application is based on patent application No. 2006-080495 filed in Japan, the contents of which are hereby incorporated by references.

As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to embraced by the claims.

Claims

1. A sheet-feed separation mechanism, comprising:

a sheet feeding roller that draws out a sheet;

a friction pad disposed oppositely to the sheet feeding roller to form a nip portion for the sheet with the sheet feeding roller; and

a pushing member that pushes the friction pad in a direction opposite to the sheet feeding direction.

2. The sheet-feed separation mechanism according to claim 1, further comprising:

a pad holder that supports the friction pad with a top portion being exposed; and

a seat that holds the pad holder in a manner so as to be able to move in forward and reverse directions with respect to the sheet feeding direction.

3. The sheet-feed separation mechanism according to claim 2, wherein:

an accommodation concave portion to accommodate the pad holder in a movable manner is provided by making a recess in a top surface of the seat.

4. The sheet-feed separation mechanism according to claim 1, wherein:

the pushing member is one of a coil spring, a plate spring, and an elastomer.

5. A sheet feeding device that draws out a sheet from a pile of sheets, comprising:

a sheet tray on which the pile of sheets is placed;

a sheet feeding roller whose peripheral surface is pressed to abut on a top surface of an uppermost sheet in the pile of the sheets at a downstream end in a sheet feeding direction of the pile of sheets;

a friction pad disposed oppositely to the sheet feeding roller to form a nip portion for the sheet with the sheet feeding roller; and

a pushing member that pushes the friction pad in a direction opposite to the sheet feeding direction.

6. The sheet feeding device according to claim 5, further comprising;

a pad holder that supports the friction pad with a top portion being exposed; and

a seat that holds the pad holder in a manner so as to be able to move in forward and reverse directions with respect to the sheet feeding direction.

7. The sheet feeding device according to claim 6, wherein:

an accommodation concave portion to accommodate the pad holder in a movable manner is provided by making a recess in a top surface of the seat.

8. The sheet feeding device according to claim 5, wherein:

the pushing member is one of a coil spring, a plate spring, and an elastomer.

9. An image reading device, comprising:

a device body including an image reading portion; and

a document feeding device that feeds a document sheet from which image information is read to the image reading portion, wherein

the document feeding device includes: a sheet tray on which a pile of the document sheet is placed; a sheet feeding roller whose peripheral surface is pressed to abut on a top surface of an uppermost sheet in the pile at a downstream end in a sheet feeding direction of the pile;

a friction pad disposed oppositely to the sheet feeding roller to form a nip portion for the sheet with the sheet feeding roller; and

a pushing member that pushes the friction pad in a direction opposite to the sheet feeding direction.

10. The image reading device according to claim 9, further comprising:

a pad holder that supports the friction pad with a top portion being exposed; and

a seat that holds the pad holder in a manner so as to be able to move in forward and reverse directions with respect to the sheet feeding direction.

11. The image reading device according to claim 10, wherein

an accommodation concave portion to accommodate the pad holder in a movable manner is provided by making a recess in a top surface of the seat.

12. The image reading device according to claim 9, wherein

the pushing member is one of a coil spring, a plate spring, and an elastomer.

13. An image forming apparatus forming an image according to image information, comprising:

a first sheet feeding device that feeds a transfer sheet;

and/or

a second sheet feeding device that feeds a document sheet from which the image information is read,

wherein one or both of the first sheet feeding device and the second sheet feeding device include:

a sheet tray on which a pile of the transfer sheet or the document sheet is placed;

a sheet feeding roller whose peripheral surface is pressed to abut on a top surface of an uppermost sheet in the pile at a downstream end in a sheet feeding direction of the pile;

a friction pad disposed oppositely to the sheet feeding roller to form a nip portion for the sheet with the sheet feeding roller; and

a pushing member that pushes the friction pad in a direction opposite to the sheet feeding direction.

14. The image forming apparatus according to claim 13, further comprising:

a pad holder that supports the friction pad with a top portion being exposed; and

a seat that holds the pad holder in a manner so as to be able to move in forward and reverse directions with respect to the sheet feeding direction.

15. The image forming apparatus according to claim 14, wherein:

an accommodation concave portion to accommodate the pad holder in a movable manner is provided by making a recess in a top surface of the seat.

16. The image forming apparatus according to claim 13, wherein:

the pushing member is one of a coil spring, a plate spring, and an elastomer.