Patent Grant
7980548
The present invention relates to a sheet feeding apparatus for picking up and feeding sheets one by one from a plurality of stacked sheets and an image forming apparatus using the sheet feeding apparatus.
Image forming apparatuses such as a recording apparatus, a printer, a facsimile apparatus, a copying machine, and multifunction machines of these apparatuses or machines have been used. The image forming apparatuses include a recording unit for recording an image (including a character, a symbol, etc.) on a recording medium such as recording paper or a plastic sheet on the basis of image information, and a reading unit for reading an image on an original. In these image forming apparatuses, in order to feed a sheet-like recording medium, the original, or the like (hereinafter referred to as a “sheet”) to an image forming portion, a sheet feeding apparatus for separated and feeding sheets one by one from a plurality of stacked sheets is used. Types of the sheet feeding apparatus include one wherein sheet feeding is performed in a state in which sheets are substantially horizontally stacked and held at a lower portion of an image forming apparatus, one wherein sheet feeding is performed in a state in which sheets are inclined and stacked at a rear surface portion of an image forming apparatus, and one wherein sheet feeding can be performed both in the above described two states.
The sheet feeding apparatus for feeding sheets which are stacked and held substantially horizontally is constituted so that the sheets stacked substantially horizontally at a lower portion of a main assembly of the image forming apparatus are fed one by one in a U-turn manner to the image forming portion by turning the sheet upside down along a substantially cylindrical recessed surface.
The sheet feeding apparatus for feeding sheets which are stacked and held in an inclined state is constituted so that the sheets which are inclined and stacked at the rear surface portion of the main assembly of the image forming apparatus are fed to the image forming portion while being gradually placed in a substantially horizontal attitude. The former sheet feeding apparatus is suitable for feeding a thin sheet such as plain paper. The latter sheet feeding apparatus is suitable for formation of a photographic-quality image since a feeding load exerted on the sheet during the image formation can be reduced.
A sheet feeding means of the sheet feeding apparatus has types such as a rotation roller type in which the roller is rotationally driven about a fixed shaft (axis), and a swing arm type in which an arm rotated about a fixed shaft (axis) supports a roller at its end portion. A separating means for separating feeding sheets one by one may be of a bank separation type utilizing a resistance at a contact surface of a sheet leading end. In addition to the bank separation type, the type of the separation means may include a friction plate separation type utilizing a sliding frictional force of a separation pad or a retarding separation type utilizing a separation roller having a torque limiter. With respect to these separation types, it is desirable that the separating means used can smoothly separate a wide range of sheets from the thin sheet such as plain paper to a thick sheet such as glossy paper for photoprinting.
When the above described separation types are compared from the viewpoint of reliability of sheet separation, a higher reliability is ensured in the order of the retarding separation type, the friction plate separation type, and the bank separation type. However, this order is reversed from the viewpoint of cost. For this reason, in the sheet feeding apparatus used for feeding principally the thin sheet such as plain paper, the bank separation type utilizing the resistance at the contact surface of the sheet leading end is employed in many cases. Further, as the sheet feeding means in those cases, the swing arm type which does not require a press-contact plate and a cam mechanism and is capable of being constituted relatively easily is employed frequently.
As is well known in the art, the swing arm type sheet feeding means used a sheet feeding roller of a so-called pendulum arm type. More specifically, the sheet feeding means is constituted so that an arm attached to a driving shaft at one end portion (base end portion) rotatably supports the sheet feeding roller at the other end portion thereof and a driving force from the driving shaft is transmitted to the sheet feeding roller through an idler gear supported at an intermediary portion of the arm. In such a swing arm type sheet feeding means, when the number of stacked sheets is changed, an angle θ formed between a surface of the sheet and a line segment connecting a contact point of the sheet feeding roller with the sheet and a center of the driving shaft is changed. As a result, a contact force acting from the sheet feeding roller onto an upper surface of the sheet is changed. This contact force is increased with a decreasing number of the stacked sheets, so that a sheet feeding performance by rotation of the sheet feeding roller is lowered as the number of the stacked sheets is increased. U.S. Patent Application Publication No. US 2004/0251592 A1 has disclosed a technique using an auxiliary arm spring 126 with respect to a sheet feeding arm 122 supporting a sheet feeding roller 121 in order to complement a contact force of the sheet feeding roller 121 when the number of the stacked sheets is large. In this case, the auxiliary arm spring 126 is used for complementing a decrease in contact force when the number of the stacked sheets is large but rather increases the contact force of the sheet feeding roller when the number of the stacked sheets is small or the sheets are not stacked.
In the above described bank separation type sheet feeding apparatus, as also shown in FIG. 11 of US 2004/0251592 A1, a method in which leading ends of sheets are pressed against an angled wall (separation wall) located at a front position of a sheet feeding tray to separate next-to-top sheets from a top sheet is employed. This separation wall also functions as a load stop to prevent a user from pushing sheets too far into a feeding path with the leading ends of the sheets passing over the sheet feeding roller when the user loads or sets the sheets such as recording paper or the like in the sheet feeding tray.
Incidentally, when sheets are set in the above described sheet feeding apparatus using the swing arm type sheet feeding means, it is necessary to push the sheet to a stacking position against the contact force of the auxiliary arm spring 126 and the self-weight of the sheet feeding arm 122. However, in the sheet feeding apparatus disclosed in US 2004/0251592 A1, inconvenience has been caused when a small amount of the thin sheets such as recording paper or the like is pushed into the sheet feeding apparatus placed in a state in which the number of stacked sheets is decreased and the contact force of the sheet feeding roller is increased. That is, the small amount of recording paper has a small rigidity, so that the sheet feeding apparatus has been accompanied with technical problems such that buckling of the sheets is induced and that setting of the sheets is difficult.
Further, in an image forming apparatus, when a sheet is fed from a sheet feeding roller to a conveying roller disposed downstream from the sheet feeding roller and then the conveying roller conveys the sheet, a drive is switched. For this reason, the image forming apparatus is constituted in some cases so that the drive of the sheet feeding roller is interrupted before the conveyance of the sheet by the conveying roller is started. In such an image forming apparatus, a positional relationship between the sheet and the sheet feeding roller during the conveyance of the sheet by the conveying roller is such that a trailing end of the sheet is still located at a position in from of a position at which the sheet trailing end completely passes through the sheet feeding roller. Accordingly, when the sheet passes through the sheet feeding roller, the resistance by the self-weight of the sheet feeding roller acts on the sheet, so that the swing arm can be raised by the fed sheet. At a subsequent moment, the raised swing arm falls by the self-weight of the swing arm to cause a force for pressing down the sheet to act on the sheet. As a result, during the sheet conveyance, a vertical reciprocating motion of the swing arm is repeated, so that a lowering in feeding (conveyance) accuracy and an occurrence of noise have been caused.
In such a sheet feeding apparatus that the apparatus is constituted so that sheet separation is effected by pressing the leading ends of the sheets against the angled wall located at the front position of the tray, the resistance against the sheet feeding is increased when an angle of the angled wall with respect to the sheets is excessively large, i.e., when the angle comes close to a right angle. As a result, the sheet feeding is unstable or cannot be performed in some cases. On the other hand, when the angle of the angled wall is gentle, a separating performance is lowered, so that a top sheet is fed together with next-to-top sheet(s) in some cases. Further, a proper angle of the angled wall varies depending on differences in material or rigidity of the sheet and in sheet feeding mechanism, so that it is difficult to stabilize a separating function only by angle adjustment of the angled wall. In order to solve these problems, in the conventional image forming apparatus, a method in which a separating pad formed of a rubber material is protruded from the surface of the angled wall to improve the separating performance has been employed. However, in such a method, a resistance acting from the protruded portion to a sheet end portion is large, so that the fed sheet has been damaged in some cases. Further, the separating pad formed of the rubber material is fixedly provided in the image forming apparatus, so that the image forming apparatus has been increased in cost.
A principal object of the present invention is, even when a small amount of sheets is set in a stacking portion, to provide a sheet feeding apparatus in which the sheets can be easily set without causing inconveniences such as buckling of the sheets and the like.
Another object of the present invention is to provide a sheet feeding apparatus capable of ensuring a sheet pressing force of a sheet feeding means and maintaining a stable sheet feeding performance even when an amount of stacked sheets is large.
According to an aspect of the present invention, there is provided a sheet feeding apparatus comprising:
a sheet stacking portion for stacking a sheet;
a sheet feeding roller for feeding the sheet stacked on the sheet stacking portion;
a supporting member, rotatably supported by a base member, for rotatably supporting the sheet feeding roller; and
a spring stretched between the base member and the supporting member;
wherein the spring acts on the sheet feeding roller so that the sheet feeding roller is pressed against the sheet with a pressing force by rotation of the supporting member when a sheet stacking amount is more than a predetermined amount and so that the pressing force is decreased when the sheet stacking amount is less than the predetermined amount.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
Hereinbelow, embodiments of the present invention will be described more specifically with reference to the drawings. In the drawings, identical reference numerals represent identical or corresponding portions or members.
The sheet S fed from the sheet feeding apparatus 10 is conveyed by a nip between a conveying roller 31 and a pinch roller 32 through an image forming portion constituted by a recording portion or a reading portion. In the case of the recording portion, an image is recorded on a sheet as a recording medium by an unshown recording head and thereafter the sheet is discharged to the outside of an apparatus main assembly by a sheet discharge roller 33 and a spur 34. On the other hand, in the case of the reading portion, an image on a sheet as an original is read by an unshown contact image sensor and thereafter the sheet is discharged on a sheet discharge tray 35 by the nip between the sheet discharge roller 33 and the spur 34.
The sheet stacking portion 11 is disposed in the neighborhood of a bottom portion of an image forming apparatus 100 and constituted so that sheets are substantially horizontally stacked and held. By stacking the sheets horizontally, the sheets can be held in a state in which distortion thereof less occurs for a long period of time. The sheet feeding portion 12 includes a rotatably supported swing arm 22. At an end portion of the swing arm 22, a sheet feeding roller 21 is supported. To the swing arm 22, a driving force transmitting mechanism, such as idler gears 28 and the like, for transmitting a driving force to the sheet feeding roller 21 is also mounted. Further, the swing arm 22 is rotatably (swingably) supported at a position upstream from the sheet feeding roller 21 in a sheet feeding direction by a swing arm supporting member 63 fixed to a sheet feeding base 25. A swing arm type sheet feeding means 20 is constituted by the swing arm 22, the sheet feeding roller 21 mounted to the swing arm 22, the driving force transmitting mechanism, etc. At a leading end portion of the sheet stacking portion 11, a leading end reference portion 23 for the sheets S is provided. In the neighborhood of the sheet stacking portion 11, a bank separation type separating portion 13 constituted by utilizing the leading end reference portion 23 is disposed. The bank separation separating portion 13 is constituted so as to be suitable for separation and feeding of a relatively thin sheet particularly such as plain paper.
First, the constitution of the sheet stacking portion 11 will be described. In
When the sheet feeding apparatus 10 is placed in a standby state, as shown in
Next, constitutions of the sheet feeding portion 12 and the separating portion 13 will be described.
In
To the sheet feeding base 25, the swing arm supporting member 63 is integrally fixed. The swing arm 22 is rotatably (swingably) attached to a lower surface of the swing arm supporting member 63. In this embodiment, the arm portions 22a and 22b constituting the swing arm 22 are rotatably supported by concentric shaft portions 25a and 25b provided to the swing arm supporting member 63. An end portion of the driving shaft 27 on the swing arm side is rotatably engaged with and supported by a projection shaft portion 25d coaxially formed at an end of the shaft portion 25a of the sheet feeding base 25. The other end portion of the driving shaft 27 is rotatably supported by a shaft-supporting hole 74 provided in the sheet feeding base 25. In this manner, the swing arm type sheet feeding means 20 is swingably supported by the shaft portions 25a and 25b concentric with the driving shaft 27. Further, the shaft portions 25a and 25b are disposed upstream from the sheet feeding roller 21 with respect to the sheet feeding direction.
In
Next, the U-turn conveying path 29 constituting a part of the sheet feeding apparatus according to this embodiment will be described.
The separating uppermost single sheet S is fed through a cylindrical reverse conveying (feeding) path (U-turn conveying path) 29 as shown in
The sheet S fed by the sheet feeding roller 21 is turned upside down by the reverse conveying path 29 and thereafter is sent in the nip between the conveying roller 31 and the pinch roller 32 through the horizontal conveying path 41. Then, the sheet feeding operation by the sheet feeding roller 21 is stopped and rotational drive of the conveying roller 31 is started. By synchronized rotation of the conveying roller 31 with the sheet discharge roller 33, the sheet S is conveyed through an image forming portion (image processing portion) 65. The thus image-formed sheet is discharged onto the sheet discharge tray 35 through the sheet discharge roller 33.
When there are no stacked sheets or the amount of the stacked sheets is small, as shown in
In the case where there is no sheet or a small amount of sheets in the sheet stacking portion 1, as shown in
That is, according to this embodiment, it is possible to easily and smoothly set the sheets with respect to the sheet stacking portion 11 without using a means such as a swing arm raising mechanism for releasing the pressing force of the sheet feeding roller 21.
In the case of a large amount of the sheets S stacked at the sheet stacking portion 11, as shown in
In a conventional swing arm type sheet feeding mechanism, a sheet feeding force by rotation of the sheet feeding roller 21 is decreased with an increasing amount of stacked sheets. For this reason, in the case of a large number of the stacked sheets, it was difficult to obtain a desired sheet feeding force in some cases. On the other hand, according to this embodiment, when the sheet stacking amount is large, it is possible to cause the pressing force by the moment of the urging spring 26 to act on the sheets in addition to the pressing force by the self-weight moment of the sheet feeding means 20. For this reason, even in the case where the sheet stacking amount is large, it is possible to generate a sufficient and stable sheet feeding force, so that a good sheet feeding performance can be maintained.
In
In
The separating member 50 is located downstream from the sheet feeding roller 21 with respect to the sheet feeding direction and is attached to the inclined surface 46 constituting the leading end reference portion 23. Further, as shown in
Referring to
That is, the uppermost sheet 43 is fed by a large frictional force between the sheet feeding roller 21 and the sheet 43, so that its leading end is movable along a separating surface constituted by the projections 51 and the valley portions 52. For this reason, only the uppermost sheet 43 is moved along the conveying path (indicated by an arrow) 45. On the other hand, the subsequent sheet 44 drawn by a small frictional force between the sheets is prevented from moving along the conveying path 45 by the separating member 50.
As shown in
Next, when rotational drive of the conveying roller 31 is started after the leading end of the sheet S is sent to the nip of the conveying roller 31, the sheet S is conveyed toward the sheet discharge roller 33 by the conveying roller 31. At this time, the attitude of the sheet S in the reverse conveying path 29 and the horizontal conveying path 41 is changed as shown in
In this embodiment, at an intermediary inner guide portion in the sheet conveying path, a rotatable member 4 is disposed so that the sheet during the conveyance can contact a peripheral surface of the rotatable member 54. Further, at a position between the sheet feeding roller 21 and the rotatable member 54 in the conveying path of the sheet S, a guide portion 55 for supporting the sheet S in contact with the sheet S is provided. This guide portion 55 is, as shown in
According to this embodiment described above, by canceling the self-weight moment of the swing arm type sheet feeding means 20 when the stacking amount of the sheets S is small, it is possible to easily and smoothly set the sheets S even in the case of setting a small amount of sheets in the sheet stacking portion 11. On the other hand, in the case where the sheet stacking amount is large, in addition to the self-weight moment of the swing arm type sheet feeding means 20, by causing moment to act on the sheets in the same direction as that of the self-weight moment, it is possible to maintain the pressing force exerted from the sheet feeding roller 21 on the sheets. As a result, it is possible to perform smooth and stable sheet feeding.
Further, this embodiment is constituted so that the plurality of arcuate projections 51 continuously disposed in the sheet feeding direction at the inclined surface of the separating member 50 disposed with an obtuse angle at the end of the sheet stacking portion 11 is provided and second and subsequent sheets are separated by the projections 51. For this reason, it is possible to separate the uppermost sheet from the second and subsequent sheets by the projections 51 in the case where a plurality of sheets is picked up.
Further, outside the tangent line connecting the sheet feeding roller 21 of the swing arm type sheet feeding means 20 and the rotatable member in the conveying path 29, the guide portion 55 contactable with the sheet S is provided, so that it is possible to prevent or alleviate the bouncing motion of the swing arm 22 when the sheet S is fed or conveyed. As a result, it is possible to prevent a lowering in conveyance accuracy and an occurrence of noise.
The above described embodiment is applicable regardless of a shape and operation method of the sheet feeding apparatus so long as the sheet feeding apparatus feeds sheets of the recording medium, the original, or the like from the sheet stacking portion one by one. Further, in the case where the image forming portion 65 is constituted by the recording portion, it is possible to employ various recording methods so long as the recording methods effect image recording on sheets by a recording means on the basis of image information. For example, it is possible to employ recording apparatuses of a laser beam type, a thermal transfer type, a heat-sensitive type, and a wire dot type, in addition to an ink jet recording apparatus for effecting recording by ejecting ink from ejection outlets of a recording head. A recording portion may be of any type including a serial type wherein recording is effected by a recording head mounted to a reciprocating carriage or a line type wherein recording is effected only by subscanning (conveyance) of a recording medium by using a recording head extending in a width direction of the recording medium.
According to the embodiment of the present invention, even in the case of setting a small amount of sheets at the sheet stacking portion, it is possible to provide a sheet feeding apparatus capable of easily setting the sheets without causing inconveniences such as buckling of the sheets and the like. Further, in the case of a large sheet stacking amount, it is possible to provide a sheet feeding apparatus capable of ensuring a sheet pressing force of the sheet feeding means and maintaining a stable sheet feeding performance.
While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims.
This application claims priority from Japanese Patent Application No. 187921/2006 filed Jul. 7, 2006, which is hereby incorporated by reference.
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