Title:
Sheet feeder capable of reducing multi feed
Kind Code:
A1


Abstract:
A sheet feeder reducing multi feed, which may include a feed roller to feed a plurality of sheets, a sole plate to press stacked sheets against the feed roller moving between an evacuation position and a pressing feed roller position, a separation pad member provided downstream from the sole plate in a feeding sheet direction switching between in contact and out of contact with the feed roller to separate the plurality of sheets one by one, and a protruding guide member provided near the separation pad member in a feeding sheet path to guide the sheets by contacting an under side of each sheet each to control the sheet's downward movement.



Inventors:
Yorimoto, Mamoru (Tokyo-to, JP)
Application Number:
11/600233
Publication Date:
05/17/2007
Filing Date:
11/16/2006
Primary Class:
International Classes:
B65H3/52
View Patent Images:
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Primary Examiner:
CICCHINO, PATRICK D
Attorney, Agent or Firm:
Harness, Dickey & Pierce P.L.C. (Reston, VA, US)
Claims:
What is claimed:

1. A sheet feeder, comprising: a feed roller to feed a plurality of sheets; a sole plate to press stacked sheets against the feed roller, which is movable between an evacuation position and a pressing feed roller position; a separation pad member provided downstream from the sole plate in a feeding sheet direction capable of switching between in contact and out of contact with the feed roller to separate each of the plurality sheets one by one in a nip press region with the feed roller; and a protruding guide member provided near the separation pad member in a feeding sheet path to guide each of the plurality sheets by contacting an under side of each of the plurality of sheets and controlling a downward movement of each of the plurality of sheets.

2. The sheet feeder of claim 1, wherein the protruding guide member is a nip press holding member in the nip press region.

3. The sheet feeder of claim 1, wherein the protruding guide member prevents each of the plurality of sheets from deviating from the feeding sheet path.

4. The sheet feeder of claim 1, wherein the protruding guide member is provided upstream from the nip press region in the feeding sheet path.

5. The sheet feeder of claim 1, wherein the protruding guide member protrudes in the feeding sheet path through the nip press region.

6. The sheet feeder of claim 1, wherein the protruding guide member protrudes higher than a sheet approaching edge part of the separation pad member in the feeding sheet path when the feed roller is in contact with the separation pad member.

7. The sheet feeder of claim 1, wherein the protruding guide member is provided as a pair of protruding guide members on both sides of the separation pad member in the feeding sheet path.

8. The sheet feeder of claim 1, wherein the protruding guide member is provided to form a gap between a tip of the protruding guide member and an undersurface of the feed roller.

9. The sheet feeder of claim 1, wherein the protruding guide member is formed with a lower friction material.

10. The sheet feeder of claim 1, wherein the protruding guide member is formed with an abrasion resistant material.

11. The sheet feeder of claim 1, wherein a height of the protruding guide member is adjustable.

12. The sheet feeder of claim 1, wherein the protruding guide member includes a roller to guide each of the plurality of sheets.

13. The sheet feeder of claim 1, wherein an angle of gradient of a tip of the protruding guide member is almost the same as a sheet feeding angle into the nip press region.

14. The sheet feeder of claim 1, wherein a downstream part of the separation pad member rotates under the feed roller and the separation pad member includes a friction pad on the nip press region side of the separation pad member.

15. The sheet feeder of claim 1, further comprising: a guide member to upwardly guide each of the plurality of sheets passing through the nip press region.

Description:

BACKGROUND

1. Field

Example embodiments generally relate to a sheet feeder that may include a feed roller, a sole plate, and/or a separation pad member, and for example to a sheet feeder capable of reducing a multi feed.

2. Discussion of the Background

A background image forming apparatus such as a printer, a copying machine, and/or a facsimile may use a sheet feeder for feeding sheet in a predetermined or desired direction one by one. A friction pad separation type sheet feeder is well known because of its low cost. Most conventional sheet feeders are capable of feeding a wide variation of sheets and are low cost.

There are at least two types of friction pad separation type sheet feeders in general. One has a feed roller and a friction pad to form a nip press region with a predetermined or given nip pressure and also has a sole plate to constantly push sheets against the feed roller. The other has a sole plate that moves between an evacuation position and a pressing feed roller position for the feeding of every sheet, and when operating is stopped, the sole plate is in the evacuation position.

FIG. 1 illustrates a configuration of a background sheet feeder. FIG. 2 also illustrates a configuration of the background sheet feeder when a multi feed occurs in the sheet feeder in FIG. 1. As shown in FIG. 1, the background sheet feeder may include a feed roller 101, a separation pad member 102, a spindle 103, a friction pad 104, and a sole plate 105. The feed roller 101 may feed a sheet P by rotating clockwise. The separation pad member 102 may move the spindle 103 as a fulcrum to form a nip press region N between the friction pad 104 and the feed roller 101 by pushing member that is not shown. The sole plate 105 pushes a stacked sheet P against the feed roller 101 by moving up and down by a driving member that is not shown.

At the time of feeding, the sole plate 105 may be moved to a pressing position shown as a chain double-dashed line from an evacuation position shown as a solid line in FIG. 1, so that a stacked sheet P is pressed against an undersurface of the feed roller 101. Holding this position, rotating the feed roller 101 feeds a top sheet into the nip press region N between the friction pad 104 and the feed roller 101. When only one sheet P is fed, the sheet P passes through the nip press region N downstream correctly. But, when a multi feed occurs, the friction pad 104 stops under sheet P, only a top sheet P is fed downstream with a rotation force of the feed roller 101.

The sole plate 105 moves between an evacuation position and a pressing feed roller position for the feeding at every sheet for feeding, and when operating is stopped, the sole plate 105 is located at the evacuation position. When the sole plate 105 is located at the evacuation position, an operator may easily set the sheets P on the sole plate 105.

As shown in FIG. 2, when the sheet P, which may include a thick sheet on top of it, is multi fed, the separation pad member 102 may move down, because a first thick sheet P1 has a stiffness or a weight to generate a down force.

If, a first thick sheet P1 and a second thick sheet P2 are multi fed, a tip part A of the separation pad member 102 is pushed down by the first thick sheet P1 and the second thick sheet P2, so that the nip press region N may be open.

Therefore, a necessary nip pressure may not be generated at the nip press region N, so that a multi feed may occur, in which the second thick sheet P2 is fed with the first thick sheet P1.

SUMMARY

Example embodiments are directed to a sheet feeder that may more effectively reduce multi feed. In example embodiments, a sheet feeder may include a feed roller to feed a plurality of sheets, a sole plate to press stacked sheets against the feed roller moving between an evacuation position and a pressing feed roller position, a separation pad member provided downstream from the sole plate in a feeding sheet direction switching between in contact and out of contact with the feed roller to separate each of the plurality of sheets one by one, and a protruding guide member provided near the separation pad member in a feeding sheet path to guide each of the plurality of sheets by contacting an under side of each sheet and controlling a downward movement of each sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 illustrates a configuration of a background sheet feeder;

FIG. 2 also illustrates a configuration of the background sheet feeder when a multi feed occurs in the sheet feeder in FIG. 1;

FIG. 3 illustrates a configuration of an electrophotographic apparatus according to example embodiments;

FIG. 4A is an example perspective diagram of a sheet feeder in a manual bypass tray of the electrophotographic apparatus of FIG. 3;

FIG. 4B is an example perspective diagram of a guide plate of the sheet feeder of FIG. 4A;

FIG. 5 is an example perspective diagram of a part of the sheet feeder of FIG. 4A;

FIG. 6 is an example perspective diagram of a pressing plate of the sheet feeder of FIG. 4A;

FIG. 7 is an example perspective diagram of a back of the pressing plate of the sheet feeder of FIG. 4A;

FIG. 8 is an example cross-sectional diagram of a part of the sheet feeder of FIG. 4A;

FIG. 9 is an example cross-sectional diagram of a part of the sheet feeder of FIG. 4A;

FIG. 10 is an example cross-sectional diagram illustrating part of the sheet feeder of FIG. 4A;

FIG. 11 is another example cross-sectional diagram of part of the sheet feeder of FIG. 4A;

FIG. 12 is another example cross-sectional diagram of part of the sheet feeder of FIG. 4A;

FIG. 13 is another example cross-sectional diagram of part of the sheet feeder of FIG. 4A;

FIG. 14 is another example cross-sectional diagram of part of the sheet feeder of FIG. 4A; and

FIG. 15 is another example cross-sectional diagram of part of the sheet feeder of FIG. 4A.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In describing example embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, particularly to FIG. 3, an electrophotographic apparatus 1 according to example embodiments is explained.

FIG. 3 illustrates an electrophotographic apparatus according to example embodiments. A main body 1 may include an image forming section 2 in the center and a feed section 3 under the image forming section 2. The feed section 3 may include sheet cassettes 4a, 4b, 4c, and 4d. The sheet cassettes 4a, 4b, 4c, and 4d may be provided like a drawer and may slide in the cross direction in FIG. 3.

A scanner 5 may be provided on the topside of the image forming section 2, which scans an original image and converts the original image to an electric signal. A catch tray 7 may be provided on the left side (downstream) of the image forming section 2, on which an ejected sheet P is stacked. A manual bypass tray 8 may be provided on the right side (upstream) of the image forming section 2 capable of opening and closing as a cover of the main body 1, which feeds a sheet P by a manual bypass.

An image forming unit 10 for each color, such as for example, a yellow (Y), a magenta (M), a cyan (C), and a black (K) is provided above a middle transfer belt 9 that is an endless belt. In the image forming unit 10, a charging unit 12, a developing unit 13, a cleaner 14, and/or an exposing unit 15a that may be a part of a light beam device 15 may be provided around a photo conductor drum 11 for each color to form an electrophotographic process.

The charging unit 12 may charge the surface of the photo conductor drum 11. The exposing unit 15a may expose the surface of the photo conductor drum 11 with laser light to form an electrostatic latent image on the surface of the photo conductor drum 11. The developing unit 13 may develop the electrostatic latent image into a visible toner image. After transferring on the surface of the photo conductor drum 11, waste toner may be removed by the cleaner 14.

A toner of each color on the photo conductor drum 11 may be transferred onto the middle transfer belt 9 to form a full color image. The full color image on the middle transfer belt 9 may be transferred onto the sheet P with a transferring device 16. The sheet P may be conveyed from the sheet cassettes 4a, 4b, 4c, and 4d or the manual bypass tray 8. The full color image on the sheet P may be fixed on the sheet P in a fixing unit 17. A sheet ejecting roller 18 may eject the sheet P onto the catch tray 7.

A conveyance path 20 may connect each of the sheet cassettes 4a, 4b, 4c, and 4d, the manual bypass tray 8, and a resist roller 19, so that the sheet P is conveyed to the resist roller 19 through the conveyance path 20. The resist roller may hold the sheet P, and send the sheet P so that the paper sheet P may have a predetermined or desired position against the toner image on the middle transfer belt 9.

A sheet feeder in example embodiments, may be applied to both the sheet cassettes 4a, 4b, 4c, and 4d, and the manual bypass tray 8. Below is an example of the manual bypass tray 8.

FIG. 4A is an example perspective diagram of a sheet feeder in a manual bypass tray of the electrophotographic apparatus of FIG. 3. FIG. 4B is an example perspective diagram of a guide plate of the sheet feeder of FIG. 4A. FIG. 5 is an example perspective diagram of a part of the sheet feeder of FIG. 4A. FIG. 6 is an example perspective diagram of a pressing plate of the sheet feeder of FIG. 4A. FIG. 7 is an example perspective diagram of a back of the pressing plate of the sheet feeder of FIG. 4A.

A sheet feeder 30 may be a friction pad separation type sheet feeder for a manual bypass tray. The sheet feeder 30 may include a feed roller 31, a sole plate 32, a friction pad 33a (shown in FIG. 5), and/or a separation pad member 33. The feed roller 31 may feed a sheet P from a stacked sheets P on the manual bypass tray 8. The sole plate 32 may be located near the feed roller 32 and may push the stacked sheets P against the feed roller 32, and may move between an evacuation position and a pressing feed roller position. The friction pad 33a may be located downstream from the sole plate 32, may be separate the fed sheet P one by one using friction force. The friction pad 33a may be provided on the separation pad member 33 that may be a plate like member.

The friction pad 33a may be made of a material with a relatively high friction coefficient, for example, a rubber, a rubber cork, a foaming urethane, a thermoplastic elastomer, etc. The separation pad member 33 may move a spindle 33b as a fulcrum. The spindle 33b may be located downstream of the separation pad member 33.

A plastic structure 34 may be provided as a lower part of the sheet feeder 30. The plastic structure 34 may include a guide plate 34a and a side guide plate 34b formed, for example, by integral moulding. The guide plate 34a and the side guide plate 34b may guide the fed sheet P.

The feed roller 31 and the separation pad member 33 may be positioned in the center of the sheet width direction that intersects perpendicularly with the feed direction of the sheet, and the feed roller 31 may be provided on a feed roller shaft 35 that has a longitudinal direction the same as the sheet width direction. Both ends of the feed roller shaft 35 may be provided on the side guide plate 34b through a roller bearing 36 that may rotate freely.

As shown in FIG. 5, the feed roller 31 has a form that a part of a cylinder is cut by a plane parallel to a center line. The feed roller 31 may have a feed roller 31a that forms a cylinder, and a cutout part 31b. A guide roller 37, which may have a disk shape and may have a smaller diameter than the feed roller 31a, may be provided on each end of the feed roller 31. The guide roller 37 is omitted on one side in FIG. 5.

A cam 38 may be provided on each end of the feed roller shaft 35. A missing tooth gear 39 for transmitting driving force to the feed roller shaft 35 may be provided on one end of the feed roller shaft 35. The missing tooth gear 39 may have a form lacking a portion of a circle, and when the missing tooth gear 39 and an input gear (not shown) mesh with each other, the feed roller shaft 35 and the feed roller 31 may be rotated. When the input gear rotates to reach a cutout part of the missing tooth gear 39, a driving force from the input gear to the missing tooth gear 39 is cut off, and rotation of the feed roller shaft 35 and the feed roller 31 may be stopped.

A feed roller position control member 40 may be fixed to the other end side of the feed roller shaft 35. A first projection 41 may be formed on the feed roller position control member 40. When a flapper 44 of a solenoid 43 catches the first projection 41, rotation of the feed roller shaft 35 and the feed roller 31 may be controlled. Further, a second projection 45 may be formed on the feed roller position control member 40. A tension spring 46 may be provided on the second projection 45, which pulls the feed roller shaft 35 and the feed roller 31 in a rotating direction of feeding a sheet P.

Rotation of the feed roller shaft 35 and the feed roller 31 may be intermittently performed as follows.

When the missing tooth gear 39 and the input gear do not mesh with each other, the solenoid 43 turns off and the flapper 44 is caught by the first projection 41. Therefore, rotation of the feed roller shaft 35 and the feed roller 31 are stopped. After that, the solenoid 43 may turn on at a certain or desired timing, the catch between the flapper 44 and the first projection 41 is not present. Then, the feed roller shaft 35 and the feed roller 31 may rotate in the feed direction by pulling force of the tension spring 46, and the rotation causes a mesh between the missing tooth gear 39 and the input gear.

After the mesh between the missing tooth gear 39 and the input gear, the missing tooth gear 39 rotates by almost 360 degrees until a non-mesh-position, and the feed roller 31 also rotates by almost 360 degrees. When the missing tooth gear 39 and the input gear do not mesh with each other, the solenoid 43 turns off and the flapper 44 is caught by the first projection 41. Therefore, the rotation of the feed roller shaft 35 and the feed roller 31 are stopped.

The guide plate 34a may be opened at a feed roller 31 position, and the separation pad member 33 may be located at the opening position. The separation pad member 33 may move a spindle 33b as a fulcrum. The friction pad 33a may be attached by, for example, a double-stick tape on the separation pad member 33, which faces the feed roller 31. A compression spring 47 may be provided under the separation pad member 33, and the friction pad 33a may press the surface of the feed roller 31 by a pressing force of the compression spring 47.

The sole plate 32 may be formed with resin. An arc projection 32a may be provided on each side of the sole plate 32 to face the cam 38, which may be located outside of a sheet P stack area. A guide roller 48 may be provided at the arc projection 32a, which contacts a surface of the cam 38. The guide roller 48 may be formed with resin, for example, polyacetal. A U-type slot may be provided on the arc projection 32a for attaching the guide roller 48, an entrance of which may be slightly narrower than a guide roller shaft. Therefore, the guide roller 48 may not easily escape. When attaching the guide roller 48, the slot may be extended by the elasticity of the resin.

A concave area 32b may be formed on the sole plate 32 center in the width direction, which may face the feed roller 31. A friction pad 49 may be attached on the concave area 32b.

A guide pin 50 may be provided near a side plate 34b on the plastic structure 34. When the sole plate 32 moves between an evacuation position and a pressing feed roller position, two pins 50 may serve as a guide. A guide hole 51 (shown in FIG. 6) may be is formed in each side of the sole plate 32 so that the guide pin 51 may pass through the guide hole 51. The guide hole 51 is located outside of a sheet P stack area so that it may not prevent feeding sheet P.

A conic compression spring 52 may be provided between the sole plate 32 and the plastic structure 34, which presses the sole plate 32 against the feed roller 31. The conic compression spring 52 may be formed around the guide pin 50, and a pressing direction by the conic compression spring 52 may be the same as an axis of the guide hole 51.

The feed roller shaft 35 and the feed roller 31 may be driven to rotate intermittently by an on-and-off of the solenoid 43 and a transfer from the input gear to the missing tooth gear 39. The cam 38 may also rotate at the time of this intermittent rotation. When the cam 38 rotates, it contacts the arc projection 32a and the guide roller 48, or it releases that contact. Then the sole plate 32 moves toward a separating direction from the feed roller 31, which may be pressed with the conic compression spring 52 against the feed roller 31.

When the feed roller 31a faces the sole plate 32, the cam 38 separates from the arc projection 32a and the guide roller 48, and the sole plate 32 is located in the pressing feed roller position pressing the stacked sheet P against the feed roller 31a. When the cam 38 contacts with the arc projection 32a and the guide roller 48, the sole plate 32 moves to the evacuation position and pressing the stacked sheet P against the feed roller 31a is released.

A pressing direction of the sole plate 52 by the conic compression spring 52 may be the same as an axis of the guide hole 51, and the cam 38 may contact the arc projection 32a and the guide roller 48 near the guide hole 51. Therefore, a bending stress of the sole plate 32 may be reduced during its movement between the evacuation position and the pressing feed roller position. Even if the sole plate 32 is made of resin, a deformation which may cause a feed performance decrease may not occur, and durability of the sole plate 32 may increase.

Further, if the sole plate 32 is made of resin, a charge of a static electricity by friction with the sheet P may be smaller, so that it may be unnecessary to connect to ground to reduce or eliminate static electricity.

FIG. 8 is an example cross-sectional diagram of a part of the sheet feeder 30 of FIG. 4A. The sheet feeder 30 may be a friction pad separation type sheet feeder for a manual bypass tray. The sheet feeder 30 may include the manual bypass tray 8, the feed roller 31, the sole plate 32, the friction pad 33a, and/or the separation pad member 33. The friction pad 33a may be provided on the separation pad member 33 that may be a board-like or plate-like member. The compression spring 47 may be provided under the separation pad member 33. The conic compression spring 52 may be provided between the sole plate 32 and the plastic structure 34.

The friction pad 33a may be made of a material with a relatively high friction coefficient, for example, a rubber, a rubber cork, a foaming urethane, a thermoplastic elastomer, etc. The separation pad member 33 may move the spindle 33b as a fulcrum. The spindle 33b may be located downstream of the separation pad member 33.

As shown in FIG. 4B, a protruding guide portion 55 may protrude from the guide plate 34a near both sides of the separation pad member 33, which guides an under side of the sheet P. A tip part 55a of the protruding guide portion 55 may be formed higher than a sheet approaching guide part 33c of the separation pad member 33 when the feed roller 31 and the friction pad 33a contacts.

FIG. 9 is an example cross-sectional diagram of a part of the sheet feeder 30 of FIG. 4A. At the time of feeding, the sole plate 32 with stacked paper P may move from the evacuation position shown as a solid line to the pressing feed roller position shown as a chain double-dashed line. Then, the sheet P is pressed against an undersurface of the feed roller 31. Holding this position and driving the feed roller 31 to rotate may cause feeding of top sheet P into the nip N between the feed roller 31 and the friction pad 33a. When only one sheet P is fed, the sheet P passes through the nip press region N downstream correctly by a rotation of the feed roller 31. But, when a multi feed occurs, the friction pad 33a stops an under sheet P, only a top sheet P is fed downstream with a rotation force of the feed roller 31. Thus, a proper feed with a separation is performed.

The sole plate 32 that moves between the evacuation position and the pressing feed roller position for feeding every sheet, and when operating is stopped, the sole plate 32 is located at the evacuation position. When the sole plate 32 is located at the evacuation position, an operator may easily set the sheets P on the sole plate 32.

FIG. 10 is an example cross-sectional diagram illustrating a multi feed in a part of the sheet feeder 30 of FIG. 4A. As shown in FIGS. 1 and 2, when the sheet P, which includes a thick sheet on top, is multi fed, the separation pad member 102 may move down, because a first thick sheet P1 may have sufficient stiffness or weight to generate a down force. As shown in FIG. 10, the down force caused by the thick sheet P1 may be reduced because the tip part 55a of the protruding guide portion 55, which protrudes higher than the sheet approaching guide part 33c, pushes the under side of the sheet P2 up and reduces or eliminates a part of the down force.

Therefore, the sheet approaching guide part 33c may not depressed by the sheet P and the nip press region N between the feed roller 31 and the separation pad member 33 may not open. As a result, a chance of a multi feed is reduced because a proper nip pressure is constantly applied. Because the down force from the thick sheet is reduced or eliminated, various types of sheets may be used easily without changing a characteristic value, for example, a nip pressure.

When the top sheet P1 is fed from the sole plate 32, the sole plate 32 falls to the evacuation position, the sole plate 32 sides of the sheets P1 and P2 hang down. Even if the sole plate 32 falls, the tip part 55a of the protruding guide portion 55 supports the sheets P1 and P2, so that the nip press region N between the feed roller 31 and the separation pad member 33 may not open. As a result, the proper nip pressure may be constantly applied, and a feed with a good separation is performed.

The protruding guide portion 55 may act as a nip press holding member at the nip press region N by contacting the sheet P that is fed into the nip N. The protruding guide portion 55 may also act as a member that prevents the sheet P from hanging down from a feeding path. Therefore, a feed with a good separation is performed constantly.

Because a depression of the protruding guide portion 55 is suppressed, conveyance guide members may be provided, for example, a guide plate 56 and a conveyance roller 57 that guide the sheet P steeply as shown in FIG. 10. As a result flexibility in the design of feeding or conveyance path may increase. A conveyance load rise due to the thick sheet at the separation pad member 33 may be reduced especially with many stacked thick sheets.

In example embodiments, the protruding guide portion 55 is provided upstream of the sheet approaching guide part 33c. Further, as shown in FIG. 9, a gap K between G (the tip part 55a) and F (an undersurface of the feed roller 31) is provided. Therefore, feeding block formed sheets P into the nip N may be reduced or prevented.

If the protruding guide portion 55 is formed of a lower friction material, for example, using resin coating, a rise of the conveyance load by frictional resistance with a sheet may be reduced, and a slip ratio rise at the time of feeding may also be reduced.

If the protruding guide portion 55 is formed of a wear-proof material, for example, a metal or a plastic containing glass fiber, a wear of the protruding guide portion 55 by contacting with the sheet may be reduced. Therefore, an effect of pressing the sheet may be maintained for a longer period, and an effect of reducing multi feed may also continue for a longer period.

An angle of gradient of the tip part 55a of the protruding guide portion 55 may be almost the same as the sheet feeding angle to the nip press region N. This may reduce a rise of a feed load, and feeding sheet into the nip press region N may be performed smoothly.

FIG. 11 is another example cross-sectional diagram of part of the sheet feeder 30 of FIG. 4A. A length of a projection of the protruding guide portion 55 may be adjustable according to a type of sheet.

As shown in FIG. 11, a rack 55b may be provided on an under part of the protruding guide portion 55 so that the rack 55b meshes with a pinion gear 58. The pinion gear 58 may be rotated using a control lever 59, so that the protruding guide portion 55 moves up and down via the rack 55b.

When the protruding guide portion 55 protrudes into a sheet conveyance path, an edge part of a thin sheet P may fold due to a large feeding angle to the friction pad 33a. But a height adjustable protruding guide portion 55 may reduce or eliminate the folding problem of the thin sheet.

When a thin sheet is twisted, a wave of the sheet may occur or an OHP sheet may be scratched. Thus, the thin sheet may generate a smaller down force at the sheet approaching guide part 33c of the separation pad member 33. In example embodiments, lowering the height of the projection of the protruding guide portion 55 may reduce an occurrence of wave and/or scratch.

FIG. 12 is another example cross-sectional diagram of part of the sheet feeder 30 of FIG. 4A. A roller 60 for guiding sheet may be provided at the tip part 55a of the protruding guide portion 55.

A thick sheet may generate a larger down force, so that a conveyance load may become larger at the protruding guide portion 55. The roller 60 may reduce the conveyance load and hold a proper conveyance force, so that various types of sheets may be used. In general, it may be necessary to increase a feed pressure for holding a proper conveyance force. In example embodiments shown in FIG. 12, it may be unnecessary to change a characteristic value, and various types of sheets may be used.

FIG. 13 is another example cross-sectional diagram of part of the sheet feeder 30 of FIG. 4A. A relay conveyance roller 61 may be provided downstream from the feed roller 31.

The relay conveyance roller 61 may be located close to the friction pad 33a of the separation pad member 33, and may be arranged as one pair on both sides of the separation pad member 33. Thus, it is possible to reduce or prevent non-sending at the time of feeding in a last sheet of OHP that tends to have a short conveyance distance due to a high slip tendency by using the relay conveyance roller 61 close to the nip press region N as much as possible.

FIG. 14 is another example cross-sectional diagram of part of the sheet feeder 30 of FIG. 4A. A separation pad member 33 may be almost horizontally oriented. A bent or inclined part 33d may be formed on a friction pad 33a at the end of the separation pad member 33, so that an inside corner M, which faces a sheet path, is formed at the bent or inclined part 33d.

When the separation pad member 33 is almost horizontally oriented, a thick sheet may easily pass through the nip press region N. The inside corner M may act to prevent multi feed because the inside corner M may resist a sheet passing.

FIG. 15 is another example cross-sectional diagram part of the sheet feeder 30 of FIG. 4A. An inside corner M on a friction pad 33a may be located at the nip press region N.

When the inside corner M is separated from the nip press region N, an edge of sheet P may swing away from the nip press region N, so that the multi feed prevents function of the inside where M may be reduced. When the inside corner M is located at the nip press region N, a movement of the edge of the sheet P is reduced, so that the multi feed preventing function the inside corner M is improved.

Any construction of example embodiments may be suitably adopted according to an apparatus's construction.

Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.

This patent specification is based on Japanese patent applications, No. JPAP2005-331412 filed on Nov. 16, 2005 in the Japan Patent Office, the entire contents of which are incorporated by reference herein.