Title:
SHEET FEEDING DEVICE AND IMAGE FORMING APPARATUS
Kind Code:
A1


Abstract:
A boundary is formed between a separating pad holding member and a separating pad in a sheet conveyance direction such that a sheet feeding device includes: a feeding roller having a feeding roller surface at a part in a rotational direction; the separating pad which separates the sheet at a holding portion between the feeding roller surface and the same; the separating pad holding member which presses the separating pad against the feeding roller; and a rolling member which is disposed coaxially with the feeding roller and abuts against the separating pad free from the holding state in cooperation with the roller surface; the feeding roller surface abutting against the separating pad holding member and the separating pad in this order, respectively, via the sheet S during the rotation of the feeding roller.



Inventors:
Muramatsu, Motoyasu (Suntou-gun, JP)
Application Number:
12/139300
Publication Date:
12/18/2008
Filing Date:
06/13/2008
Assignee:
CANON KABUSHIKI KAISHA (Tokyo, JP)
Primary Class:
International Classes:
B65H5/06
View Patent Images:



Primary Examiner:
SEVERSON, JEREMY R
Attorney, Agent or Firm:
Venable LLP (New York, NY, US)
Claims:
What is claimed is:

1. A sheet feeding device comprising: a feeding roller having a roller surface, on which a sheet is fed, at a part in a rotational direction; a separating pad which is disposed opposite to the feeding roller and the sheets are separated between the separating pad and the roller surface; a separating pad holding member which holds the separating pad therein and presses the separating pad against the feeding roller; and a rolling member which abuts against the separating pad free from the abutting state with the roller surface; wherein the roller surface abuts against the separating pad holding member and the separating pad in this order via the sheet during the rotation of the feeding roller.

2. The sheet feeding device according to claim 1, wherein a friction coefficient of the surface of the separating pad holding member is smaller than that of the surface of the separating pad.

3. The sheet feeding device according to claim 1, wherein first and second regions, against which the roller surface of the feeding roller abuts, are set, and further, out of the boundary between the separating pad holding member and the separating pad, a boundary of the second region is formed more upstream in a sheet conveyance direction than a boundary of the first region.

4. The sheet feeding device according to claim 3, wherein the rolling members are disposed on both sides at the roller surface of the feeding roller in a sheet widthwise direction perpendicular to the sheet conveyance direction, and further, the second regions of the separating pad holding member are disposed on both sides of the first region whose boundary has a width smaller than a distance between the rolling members.

5. A sheet feeding device comprising: a feeding roller having a roller surface, on which a sheet is fed, at a part in a rotational direction; a separating pad which is disposed opposite to the feeding roller and the sheets are separated between the separating pad and the roller surface; a separating pad holding member which holds the separating pad therein and presses the separating pad against the feeding roller; and a rolling member which abuts against the separating pad free from the abutting state with the roller surface; wherein the separating pad holding member holds a sliding member, which is made of a material harder than the separating pad holding member, in a region, against which the roller surface abuts, and upstream of the separating pad in a sheet conveyance direction, and the roller surface abuts against the sliding member and the separating pad in this order via the sheet during the rotation of the feeding roller.

6. The sheet feeding device according to claim 5, wherein a boundary between the separating pad and the separating pad holding member is formed more upstream in a sheet conveyance direction than a boundary between the separating pad and the sliding member, against which the roller surface of the feeding roller abuts.

7. The sheet feeding device according to claim 6, wherein the rolling members are disposed on both sides at the roller surface of the feeding roller in a sheet widthwise direction perpendicular to the sheet conveyance direction, and further, the boundaries between the separating pad and the separating pad holding member are formed on both sides of the boundary between the separating pad and the sliding member whose boundary has a width smaller than a distance between the rolling members.

8. A sheet feeding device comprising: a feeding roller having a roller surface, on which a sheet is fed, at a part in a rotational direction; a separating pad which is disposed opposite to the feeding roller and the sheets are separated between the separating pad and the roller surface; a separating pad holding member which holds the separating pad therein and presses the separating pad against the feeding roller; and a rolling member which abuts against the separating pad free from the abutting state with the roller surface; wherein the separating pad holding member holds a sliding member having a friction coefficient smaller than that of the separating pad in a region, against which the roller surface abuts, and upstream of the separating pad in a sheet conveyance direction, and the roller surface abuts against the sliding member and the separating pad in this order via the sheet during the rotation of the feeding roller.

9. The sheet feeding device according to claim 8, wherein a boundary between the separating pad and the separating pad holding member is formed more upstream in a sheet conveyance direction than a boundary between the separating pad and the sliding member, against which the roller surface of the feeding roller abuts.

10. The sheet feeding device according to claim 9, wherein the rolling members are disposed on both sides at the roller surface of the feeding roller in a sheet widthwise direction perpendicular to the sheet conveyance direction, and further, the boundaries between the separating pad and the separating pad holding member are formed on both sides of the boundary between the separating pad and the sliding member whose boundary has a width smaller than a distance between the rolling members.

11. An image forming apparatus comprising: a recording unit which records an image on a sheet to be recorded; and a sheet feeding device which feeds the sheet toward the recording unit; the sheet feeding device including: a feeding roller having a roller surface, on which a sheet is fed, at a part in a rotational direction; a separating pad which is disposed opposite to the feeding roller and the sheets are separated between the separating pad and the roller surface; a separating pad holding member which holds the separating pad therein and presses the separating pad against the feeding roller; and a rolling member which abuts against the separating pad free from the abutting state with the roller surface; wherein the roller surface abuts against the separating pad holding member and the separating pad in this order via the sheet during the rotation of the feeding roller.

12. The image forming apparatus according to claim 11, wherein a friction coefficient of the surface of the separating pad holding member is smaller than that of the surface of the separating pad.

13. The image forming apparatus according to claim 11, wherein first and second regions, against which the roller surface of the feeding roller abuts, are set, and further, out of the boundary between the separating pad holding member and the separating pad, a boundary of the second region is formed more upstream in a sheet conveyance direction than a boundary of the first region.

14. The image forming apparatus according to claim 13, wherein the rolling members are disposed on both sides at the roller surface of the feeding roller in a sheet widthwise direction perpendicular to the sheet conveyance direction, and further, the second regions of the separating pad holding member are disposed on both sides of the first region whose boundary has a width smaller than a distance between the rolling members.

15. An image forming apparatus comprising: a recording unit which records an image on a sheet to be recorded; and a sheet feeding device which feeds the sheet toward the recording unit; the sheet feeding device including: a feeding roller having a roller surface, on which a sheet is fed, at a part in a rotational direction; a separating pad which is disposed opposite to the feeding roller and the sheets are separated between the separating pad and the roller surface; a separating pad holding member which holds the separating pad therein and presses the separating pad against the feeding roller; and a rolling member which abuts against the separating pad free from the abutting state with the roller surface; wherein the separating pad holding member holds a sliding member, which is made of a material harder than the separating pad holding member, in a region, against which the roller surface abuts, and upstream of the separating pad in a sheet conveyance direction, and the roller surface abuts against the sliding member and the separating pad in this order via the sheet during the rotation of the feeding roller.

16. The image forming apparatus according to claim 15, wherein a boundary between the separating pad and the separating pad holding member is formed more upstream in a sheet conveyance direction than a boundary between the separating pad and the sliding member, against which the roller surface of the feeding roller abuts.

17. The image forming apparatus according to claim 16, wherein the rolling members are disposed on both sides at the roller surface of the feeding roller in a sheet widthwise direction perpendicular to the sheet conveyance direction, and further, the boundaries between the separating pad and the separating pad holding member are formed on both sides of the boundary between the separating pad and the sliding member whose boundary has a width smaller than a distance between the rolling members.

18. An image forming apparatus comprising: a recording unit which records an image on a sheet to be recorded; and a sheet feeding device which feeds the sheet toward the recording unit; the sheet feeding device including: a feeding roller having a roller surface, on which a sheet is fed, at a part in a rotational direction; a separating pad which is disposed opposite to the feeding roller and the sheets are separated between the separating pad and the roller surface; a separating pad holding member which holds the separating pad therein and presses the separating pad against the feeding roller; and a rolling member which abuts against the separating pad free from the holding state in cooperation with the roller surface; wherein the separating pad holding member holds a sliding member having a friction coefficient smaller than that of the separating pad in a region, against which the roller surface abuts, and upstream of the separating pad in a sheet conveyance direction, and the roller surface abuts against the sliding member and the separating pad in this order via the sheet during the rotation of the feeding roller.

19. The image forming apparatus according to claim 18, wherein a boundary between the separating pad and the separating pad holding member is formed more upstream in a sheet conveyance direction than a boundary between the separating pad and the sliding member, against which the roller surface of the feeding roller abuts.

20. The image forming apparatus according to claim 19, wherein the rolling members are disposed on both sides at the roller surface of the feeding roller in a sheet widthwise direction perpendicular to the sheet conveyance direction, and further, the boundaries between the separating pad and the separating pad holding member are formed on both sides of the boundary between the separating pad and the sliding member whose boundary has a width smaller than a distance between the rolling members.

Description:

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeding device which separates sheets such as originals or recording sheets one by one and feeds them, and an image forming apparatus having the sheet feeding device such as a copying machine, a facsimile or a printer.

2. Description of the Related Art

In an image forming apparatus such as a copying machine or a printer, the stability of feeding performance and the reduction of an operational noise has been required for a sheet feeding device which separates sheets such as originals or recording sheets one by one and feeds them. There has been conventionally known a sheet feeding device having a system in which sheets are separated one by one by a semicircular feeding roller and a separating pad pressed against the feeding roller. In the sheet feeding device of the separation system, vibrations may be generated between the feeding roller and the separating pad according to a type of sheet to be fed, and further, the vibrations may cause an abnormal noise (i.e., a chattering noise).

In view of this, there has been proposed a technique which provides a vibration suppressing member for a separating pad so as to prevent any vibration of the separating pad, thereby preventing any generation of an abnormal noise, as disclosed in Japanese Patent Application Laid-open No. 8-91608. This configuration can produce an effect of suppressing the vibration of the separating pad, generated due to a slide-contact of a sheet to be fed at a predetermined speed with the separating pad.

However, even the above-described prior art cannot prevent any vibration caused by friction between the sheet and the separating pad generated at the time of the abutment of the feeding roller rotated during the sheet feeding against the separating pad via the sheet, and therefore, the vibration causes an abnormal noise (i.e., a chattering noise).

In order to suppress any generation of the abnormal noise, it is devised that a pressing force of the separating pad against the feeding roller is reduced or a friction coefficient of the separating pad is reduced. However, this degrades the separability of the sheet by the separating pad, thereby achieving a satisfactory separating/feeding performance.

Moreover, with a configuration in which a collision is alleviated during the abutment of the feeding roller against the separating pad, it is devised that the rotational speed of the feeding roller is reduced down to a speed enough to prevent any generation of the abnormal noise. However, this reduces a sheet conveyance speed.

SUMMARY OF THE INVENTION

The present invention suppresses any vibration generated during an abutment of a feeding roller against a separating pad without any reduction of a sheet conveyance speed or any degradation of a separating/feeding performance, so as to prevent any generation of an abnormal noise (i.e., a chattering noise) due to the vibration.

According to a typical aspect of the present invention, a sheet feeding device includes: a feeding roller having a roller surface, on which a sheet is fed, at a part in a rotational direction; a separating pad which is disposed opposite to the feeding roller and the sheets are separated between the separating pad and the roller surface; a separating pad holding member which holds the separating pad therein and presses the separating pad against the feeding roller; and a rolling member which abuts against the separating pad free from the abutting state with the roller surface; wherein the roller surface abuts against the separating pad holding member and the separating pad in this order via the sheet during the rotation of the feeding roller.

According to the present invention, the vibration generated during the abutment of the feeding roller against the separating pad can be suppressed without any reduction of the sheet conveyance speed or any degradation of the separating/feeding performance, so that the generation of an abnormal noise (i.e., a chattering noise) due to the vibration can be prevented.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating the configuration of an image forming apparatus provided with a sheet feeding device;

FIG. 2 is a perspective view illustrating essential parts of the sheet feeding device;

FIG. 3 is a cross-sectional view illustrating a standby state before a sheet separating/feeding operation by the sheet feeding device;

FIG. 4 is a cross-sectional view illustrating a state during sheet separation/feeding by the sheet feeding device;

FIG. 5 is a cross-sectional view illustrating a state during sheet separation/conveyance by the sheet feeding device;

FIG. 6 is a cross-sectional view illustrating the state of the sheet feeding device during the sheet conveyance;

FIGS. 7A and 7B are views illustrating the configuration of a separating pad in the sheet feeding device in a first exemplary embodiment;

FIG. 8 is a cross-sectional view illustrating, in enlargement, a sheet feeding operation by the sheet feeding device;

FIG. 9 is another cross-sectional view illustrating, in enlargement, the sheet feeding operation by the sheet feeding device;

FIGS. 10A and 10B are views illustrating the configuration of a separating pad in a sheet feeding device in a second exemplary embodiment;

FIGS. 11A and 11B are views illustrating the configuration of a separating pad in a sheet feeding device in a third exemplary embodiment; and

FIGS. 12A and 12B are views illustrating the configuration of a separating pad in a sheet feeding device in a fourth exemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, exemplary embodiments according to the present invention will be illustratively described in detail in reference to the attached drawings. Here, dimensions, materials and shapes of component parts and their relative arrangement described in the exemplary embodiments below shall be appropriately varied according to configurations or various conditions of an apparatus, to which the present invention is applied. As a consequence, the scope of the present invention is not limited to only those, unless specified otherwise.

First Exemplary Embodiment

FIG. 1 is a view exemplifying the schematic configuration of an image forming apparatus provided with a sheet feeding device, and FIG. 2 is a perspective view illustrating essential parts of the sheet feeding device.

As shown in FIGS. 1 and 2, an inside plate 101 is disposed in a sheet cassette 114, and thus, presses upward sheets S stacked thereon by force of an urging spring 113. A feeding roller 102 is fixed to a support shaft 108, to be rotatably supported thereon. An uppermost sheet out of the sheets S pressed up by the inside plate 101 abuts at the tip thereof against the feeding roller 102. The feeding roller 102 has a roller surface 102r which feeds the sheet thereon. The roller surface 102r is formed into an arcuate shape in cross section, and is disposed at a part of the feeding roller in a rotational direction. Here, the feeding roller 102 has the roller surface 102r formed into a semicircle in cross section. A front portion 102ra illustrated in FIG. 8 of the roller surface 102r in the rotational direction is formed into a smoothly arcuate shape in such a manner that a radius from the axis of the support shaft 108 becomes gradually smaller.

Circular abutment rollers (i.e., rolling members) 109 are rotatably disposed in the support shaft 108 having the feeding roller 102 fixed thereto on both sides of the feeding roller 102 in a sheet widthwise direction perpendicular to a sheet conveyance direction. In other words, the abutment rollers 109 are rotatably disposed coaxially with the feeding roller 102.

A separating pad 104 faces the feeding roller 102, and separates the sheets one by one at a holding portion between the roller surface 102r and the same. A separating pad holding member 103 holds the separating pad 104 therein, and further, presses the separating pad 104 against the feeding roller 102. The separating pad holding member 103 is disposed under the feeding roller 102 in an oscillatable manner within a predetermined range on a hinge h. The separating pad 104 is disposed at an upper portion of the separating pad holding member 103, and further, abuts against a lower portion of the feeding roller 102. A spring 105 urges the separating pad holding member 103 toward the feeding roller 102. A conveying guide 106 serves as a conveyance path for the sheet S conveyed by the feeding roller 102. Conveying rollers 107 convey the sheet S to a next process.

The conveyed sheet S is further conveyed by a transfer belt 115, is subjected to transfer of a toner image from each of photosensitive drums 110K, 110C, 110M and 110Y and to fixture by a heat fixing unit 111, and thereafter, is discharged onto a discharge tray 112.

A radius Ra of the roller surface 102r of the feeding roller 102 is greater than a radius Rb of the abutment roller 109 (Ra>Rb). Therefore, when the abutment roller 109 is fixed to the support shaft 108, the peripheral surface of the abutment roller 109 is located inside of the roller surface 102r. As a consequence, the abutment roller 109 does not abut against the separating pad 104 in a holding state of the roller surface 102r of the feeding roller 102 and the separating pad 104: in contrast, the abutment roller 109 abuts against the separating pad 104 which is released from the holding state in cooperation with the roller surface 102r of the feeding roller 102.

FIG. 3 is a cross-sectional view schematically illustrating a standby state before the sheet is separated and fed. The inside plate 101 having the sheets S stacked thereon is lifted upward by the urging spring 113, as illustrated in FIG. 1. In this manner, the inside plate 101 comes to a halt in the state in which the tip of the uppermost sheet out of the sheets S abuts against the abutment rollers 109, and then, the sheet can be turned to a freely fed state. Moreover, the separating pad 104 is in an abutment state against the abutment rollers 109 by the energization of the spring 105. That is to say, the position of the separating pad 104 in the standby state depends upon the abutment roller 109.

FIG. 4 is a cross-sectional view schematically illustrating a state during sheet separation/feeding. Upon start of a sheet feeding operation, the rotation of the feeding roller 102 enables the roller surface 102r of the feeding roller 102 to abut against the uppermost sheet S, which is then fed, as illustrated in FIG. 4. The fed sheet S is conveyed to between the conveying rollers 107 through a nip unit serving as a holding unit defined between the feeding roller surface 102r and the separating pad 104.

Here, the sheet S held between the feeding roller surface 102r and the separating pad 104 is pressed against the separating pad 104 by the feeding roller 102. An interrelationship among a friction μ1 between the separating pad 104 and the sheet, a friction μ2 between the sheets, and a friction μ3 between the sheet and the feeding roller 102 is established in such a manner as to meet an inequality of μ213. Thus, even if the plurality of sheets S are fed by the feeding roller 102 at the same time, the sheets can be separated from each other, and then, are fed one by one.

The feeding roller 102 is rotated once by a clutch mechanism, not illustrated. At this time, the tip of the sheet S is conveyed up to between the conveying rollers 107, as illustrated in FIG. 5. Thereafter, the feeding roller 102 is stopped such that portions, at which the roller surface 102r of the feeding roller 102 is cut out, that is, the abutment rollers 109 face the separating pad 104, as illustrated in FIG. 6.

At this time, the conveying rollers 107 continue conveying the sheet S. Therefore, the sheet S passing between the abutment rollers 109 and the separating pad 104 is conveyed by the conveying rollers 107 while remaining held between the abutment rollers 109 and the separating pad 104. Here, the abutment rollers 109 are not fixed to the support shaft 108, and thus, are rotated together with the sheet S to be conveyed. The abutment rollers 109 are rotated in this manner, and further, the sheet S is conveyed in contact with the separating pad 104. Consequently, the dual feeding of the sheets S can be prevented with a small back tension against a conveyance force.

As illustrated in FIG. 4, the feeding roller 102 abuts against the separating pad 104 via the sheet S during the sheet separating operation. At this time, the separating pad holding member 103 is pressed by the feeding roller 102, to be turned on the hinge h. Therefore, the feeding roller 102 abruptly receives a reaction from the spring 105 of the separating pad holding member 103, and further, the sheet S and the separating pad 104 strongly slide each other at the abutment portion against the feeding roller surface 102r. In this way, a stick-slip (i.e., a frictional vibration phenomenon) occurs between the sheet S and the separating pad 104 according to the type of sheet S or an environmental ambient (such as a temperature or a humidity), thereby raising an undesired possibility of generation of an abnormal noise due to the stick-slip (hereinafter referred to as “a strange noise of a pad”). The stick-slip signifies a phenomenon in which objects repeatedly slide on or interfere with a given surface by friction therebetween when the objects take a sliding motion, thereby inducing a frictional vibration.

Although the generation of the strange noise of the pad may be suppressed by reducing a spring pressure of the spring 105 which presses the separating pad holding member 103, it is difficult to suppress the generation of the strange noise of the pad since the dual feeding occurs due to the unsatisfactory separation of the sheets S from each other according to the type of sheet S. Otherwise, it may be construed that the strange noise of the pad is prevented by varying the friction coefficients of the feeding roller 102 and the separating pad 104, but it is difficult to find a combination of materials capable of coping with the type of sheet S, an environmental change and the like.

In view of this, a boundary between the separating pad holding member 103 and the separating pad 104 in a sheet conveyance direction is set in such a manner that the feeding roller surface 102r abuts against the separating pad holding member 103 and the separating pad 104 in this order via the sheet S, respectively, during the rotation of the feeding roller 102. This will be described in detail in reference to FIGS. 7 to 9.

A boundary 103b between the separating pad holding member 103 and the separating pad 104 is illustrated in FIGS. 7A and 7B. The front portion 102ra of the feeding roller surface 102r first abuts against the vicinity of the boundary 103b of the separating pad holding member 103 during one rotation of the feeding roller 102, as illustrated in FIG. 8 (hereinafter referred to as “a point A1”). Next, the peripheral surface of the roller surface 102r abuts against the separating pad 104 via the sheet S, as illustrated in FIG. 9 (hereinafter referred to as “a point A2”). In this manner, the boundary 103b is defined between the separating pad holding member 103 and the separating pad 104. When the sheet S reaches the point A2, the separating pad holding member 103 and the feeding roller surface 102r are separated from each other.

Specifically, it is designed such that the roller surface 102r of the feeding roller 102 abuts against the separating pad holding member 103 at the point A1 before the abutment against the separating pad 104 at the point A2 via the sheet S. Since the separating pad holding member 103 is made of a resin material (here, PPE and PS), the friction coefficient of the surface is smaller than that of the separating pad 104. Therefore, upon the abutment of the feeding roller 102 via the sheet S, the separating pad holding member 103 and the sheet S slide each other, so that no stick-slip occurs between the feeding roller 102 and the sheet S, thereby preventing any occurrence of the strange noise of the pad. At this time, the separating pad holding member 103 has been already maintained substantially at an angle, at which the sheet separating operation is performed, owing to the previous abutment against the feeding roller 102. As a consequence, when the separating pad 104 and the feeding roller 102 next abut against each other via the sheet S, they can abut against each other without any great change in angle. Thus, the separating pad 104 and the sheet S cannot strongly slide each other at the time of the abutment against the feeding roller 102, thereby preventing any occurrence of the strange noise of the pad.

Incidentally, in the case where the boundary 103b between the separating pad holding member 103 and the separating pad 104 is formed excessively downstream of the above-setting position in the sheet conveyance direction, as follows: the feeding roller surface 102r remains abutting against the separating pad holding member 103 even after the front portion 102ra abuts against the separating pad holding member 103, and therefore, cannot satisfactorily abut against the separating pad 104 via the sheet, thereby inducing the dual feeding of the sheet. In contrast, in the case where the boundary 103b between the separating pad holding member 103 and the separating pad 104 is formed upstream of the above-set position in the sheet conveyance direction, the feeding roller surface 102r cannot abut against the separating pad holding member 103 via the sheet, resulting in the occurrence of the strange noise of the pad, like in the prior art. Alternatively, in the case where the boundary 103b is formed more upstream, the tip of the fed sheet S intrudes while forming an obtuse angle with respect to the separating pad 104, and therefore, the sheet S is liable to be deficiently conveyed due to its interference.

As described above, in the present exemplary embodiment, the boundary 103b between the separating pad holding member 103 and the separating pad 104 is set in such a manner that the feeding roller surface 102r abuts against the separating pad holding member 103 and the separating pad 104 in this order via the sheet S, respectively. As a result, the vibration generated during the abutment of the feeding roller 102 against the separating pad 104 via the sheet can be suppressed without any reduction of the sheet conveyance speed or any degradation of the separating/feeding performance, thus preventing any generation of the abnormal noise (i.e., a chattering noise) due to the vibration.

Second Exemplary Embodiment

A sheet feeding device in a second exemplary embodiment is described in reference to FIGS. 10A and 10B. Here, a mechanical structure in the present exemplary embodiment is substantially identical to that in the first exemplary embodiment. Therefore, reference numerals illustrated in FIGS. 1 to 9 are used, and further, constituent elements designated by the reference numerals will not be described. In addition, an operation in the second exemplary embodiment also is identical to that in the first exemplary embodiment, and therefore, its description will be omitted below.

In the present exemplary embodiment, out of boundaries 103b between a separating pad holding member 103 and a separating pad 104, boundaries 103b2 in a second region are formed in a sheet conveyance direction upstream of another boundary 103b1 in a first region, against which a feeding roller surface 102r abuts. Here, a distance t between the boundary 103b1 and the boundary 103b2 is set to 0.8 mm, although a tip of a fed sheet S interferes with the separating pad 104, to be liable to be deficiently conveyed when the boundaries 103b2 are formed more upstream in the sheet conveyance direction (here, the distance t is greater than 2 mm).

The second regions in the separating pad holding member 103 are formed on both sides of the first region (having a width 103w) in a sheet widthwise direction. Moreover, the width of the boundary 103b1 of the first region (having the width 103w) is set to be narrower than a distance between abutment rollers 109. Here, the width 103w of the first region is set to be equal to a length of the feeding roller surface 102r in the sheet widthwise direction.

A front portion 102ra in the feeding roller surface 102r first abuts against the vicinity of the boundary 103b1 of the separating pad holding member 103 during one rotation of the feeding roller 102, as illustrated in FIG. 8 (hereinafter referred to as “a point A1”). Next, the peripheral surface of the feeding roller surface 102r abuts against the separating pad 104 via the sheet S, as illustrated in FIG. 9 (hereinafter referred to as “a point A2”). In this manner, the boundary 103b1 is formed between the separating pad holding member 103 and the separating pad 104. When the sheet S reaches the point A2, the separating pad holding member 103 and the feeding roller surface 102r are separated from each other.

Additionally, as illustrated in FIGS. 10A and 10B, out of the boundaries 103b between the separating pad holding member 103 and the separating pad 104, only the boundary 103b1 formed at the center projects in the sheet conveyance direction in comparison with the boundaries 103b2 formed on both sides in the sheet widthwise direction. As a consequence, the tip of the sheet S abuts against the separating pad 104 earlier than the boundary 103b1 within a range of the boundaries 103b2 at both ends of the separating pad 104. Therefore, in the case of dual feeding of sheets, a function of preventing any dual feeding is inhibited from being degraded by a sheet separating effect of mutually loosening the sheets S. Incidentally, since the feeding roller surface 102r does not face the regions of the boundaries 103b2, even if the tip of the sheet S first abuts against the separating pad 104 prior to abutment against the vicinity of the boundary 103b1 of the separating pad holding member 103, no abnormal noise can occur due to a vibration.

Third Exemplary Embodiment

A sheet feeding device in a third exemplary embodiment is described in reference to FIGS. 11A and 11B. Here, a mechanical structure in the present exemplary embodiment is substantially identical to those in the first and second exemplary embodiments. Therefore, reference numerals illustrated in FIGS. 1 to 9 are used, and further, constituent elements designated by the reference numerals will not be described. In addition, an operation in the third exemplary embodiment also is identical to those in the first and second exemplary embodiments, and therefore, its description will be omitted below.

In the present exemplary embodiment, a separating pad holding member 103 holds a sliding member 103s, which is made of a material harder than the separating pad holding member 103 and has a high surface performance, in a region (having a width 103w), against which a feeding roller surface 102r abuts, and upstream in a sheet conveyance direction of a separating pad 104. Here, an SUS plate is used as the sliding member 103s. In this manner, a boundary between the sliding member 103s and the separating pad 104 in the sheet conveyance direction is set in such a manner that the feeding roller surface 102r abuts against the sliding member 103s and the separating pad 104 in this order via a sheet, respectively, during rotation of a feeding roller 102.

Moreover, out of boundaries 103b between the separating pad holding member 103 and the separating pad 104 in the sheet conveyance direction, boundaries 103b2 between the separating pad holding member 103 and the separating pad 104 are formed upstream of another boundary 103b1 between the sliding member 103s and the separating pad 104 in the sheet conveyance direction.

Furthermore, the boundaries 103b2 between the separating pad holding member 103 and the separating pad 104 in a sheet widthwise direction are formed on both sides of the boundary 103b1 between the sliding member 103s and the separating pad 104. Additionally, the width (the width 103w) of the boundary 103b1 of the sliding member 103s is set to be narrower than a distance between abutment rollers 109.

In the case where the separating pad holding member 103 is made of a soft material (e.g., a resin such as ABS), the separating pad holding member 103 may be cut off by a tip of a sheet S when the feeding roller 102 repeatedly abuts against the separating pad holding member 103 via the sheet S. Otherwise, in the case where the separating pad holding member 103 is made of a material having a poor surface performance (e.g., a resin material containing a large quantity of glass), the poor surface performance may raise a fear of occurrence of deficient conveyance, for example, an interference of the tip of the sheet S with the separating pad holding member 103. In view of this, the use of the sliding member 103s (i.e., the SUS plate), like in the present exemplary embodiment, enables the sheet to be stably conveyed.

A front portion 102ra first abuts against the vicinity of the boundary 103b1 of the sliding member 103s via the sheet during one rotation of the feeding roller 102. Next, the peripheral surface of the feeding roller surface 102r abuts against the separating pad 104 via the sheet. Therefore, during the slide between the feeding roller 102 and the sliding member 103s via the sheet, the sheet and the sliding member 103s slide each other, so that no stick-slip occurs between the feeding roller 102 and the sheet. As a consequence, the occurrence of the strange noise of the pad can be prevented more than in the above-described exemplary embodiments.

Incidentally, the sliding member 103s may be made of other materials having a small surface friction coefficient, thus suppressing the strange noise of the pad in the same manner.

Fourth Exemplary Embodiment

A sheet feeding device in a fourth exemplary embodiment is described in reference to FIGS. 12A and 12B. Here, a mechanical structure in the present exemplary embodiment is substantially identical to those in the first, second and third exemplary embodiments. Therefore, reference numerals illustrated in FIGS. 1 to 9 are used, and further, constituent elements designated by the reference numerals will not be described. In addition, an operation in the fourth exemplary embodiment also is identical to those in the first, second and third exemplary embodiments, and therefore, its description will be omitted below.

In the present exemplary embodiment, a separating pad holding member 103 holds a sliding member 103e having a friction coefficient smaller than that of the separating pad 104 in a region (having a width 103w), against which a feeding roller surface 102r abuts, and upstream of a separating pad 104 in a sheet conveyance direction. Here, an urethane- or rubber-based elastomer member is used as the sliding member 103e. In addition, the friction coefficient of the separating pad 104 is 0.9 to 0.8 whereas the friction coefficient of the sliding member (i.e., the elastomer member) 103e is 0.6 to 0.5. In this manner, a boundary between the sliding member 103e and the separating pad 104 in a sheet conveyance direction is set in such a manner that the feeding roller surface 102r abuts against the sliding member 103e and the separating pad 104 in this order via a sheet, respectively, during rotation of a feeding roller 102.

Moreover, out of boundaries 103b between the separating pad holding member 103 and the separating pad 104 in the sheet conveyance direction, boundaries 103b2 between the separating pad holding member 103 and the separating pad 104 are formed upstream of another boundary 103b1 between the sliding member 103e and the separating pad 104 in the sheet conveyance direction.

Furthermore, the boundaries 103b2 between the separating pad holding member 103 and the separating pad 104 in a sheet widthwise direction are formed on both sides of the boundary 103b1 between the sliding member 103e and the separating pad 104. Additionally, the width (the width 103w) of the boundary 103b1 of the sliding member 103e is set to be narrower than a distance between abutment rollers 109.

A front portion 102ra first abuts against the vicinity of the boundary 103b1 of the sliding member 103e via the sheet during one rotation of the feeding roller 102. Next, the peripheral surface of the roller surface 102r abuts against the separating pad 104 via the sheet. Therefore, also during the slide between the feeding roller 102 and the sliding member 103e via the sheet, the sheet and the sliding member 103e slide each other, so that no stick-slip occurs between the feeding roller 102 and the sheet. As a consequence, the occurrence of a strange noise of the pad can be prevented more than in the above-described first and second exemplary embodiments.

Additionally, the sliding member 103e has the frictional coefficient smaller than those of the feeding roller 102 and the separating pad 104, thereby not only preventing any strange noise of the pad but also separating sheets one by one even when a plurality of sheets dually fed slide each other between the feeding roller 102 and the sliding member 103e. Alternatively, the sliding member 103e can assist the separation by the separating pad 104, thus preventing any deficiency of dual feeding.

Other Exemplary Embodiments

In the above-described exemplary embodiments, a printer has exemplified the image forming apparatus, but the present invention is not limited to this. For example, the present invention may be applied to other image forming apparatuses such as a copying machine and a facsimile, a further image forming apparatus for a composite machine having a combination of functions of a copying machine and a facsimile, or an image reading apparatus such as a scanner. The similar effects can be produced by applying the present invention to the sheet feeding device for use in the aforementioned image forming apparatus or image reading apparatus.

Although the sheet feeding device integrally provided in the image forming apparatus has been illustrated in the above-described exemplary embodiments, the present invention is not limited to this. For example, the present invention may be applicable to a sheet feeding device which is detachably attached to an image forming apparatus. The similar effects can be produced by applying the present invention to the sheet feeding device.

In addition, although the sheet feeding device which feeds the sheets one by one to a recording unit which records an image on a sheet such as a recording sheet to be recorded has been illustrated in the above-described exemplary embodiments, the present invention is not limited to this. For example, the similar effects can be produced by applying the present invention to the sheet feeding device which feeds the sheets one by one to a reading unit which reads an image on a sheet such as an original to be read.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2007-159683, filed Jun. 18, 2007, which is hereby incorporated by reference herein in its entirety.