Sheet feeder

Abstract

 A sheet feeder according to the invention comprises a housing (100) provided with a sheet accommodation space in which a plurality of sheets are to be stacked and held; a separation plate (11) which is arranged against the forward edge of the sheets held in the housing and whose surface in contact with the forward edge of the sheets is substantially perpendicular to the sheet face; a feed roller (1), arranged close to the separation plate, for feeding the uppermost one of the sheets held in the housing in the forward direction while in contact with the face of that sheet; and pressurizing means (9,10) for applying pressure to the sheets toward the feed roller. The separation plate has a tapered face (11a) at its forward end inclined in the sheet feeding direction, so that the forward edge of the top sheet in contact with the feed roller run against the tapered face. This arrangement facilitates separation of the top sheet from the next even if the sheets are thicker than usual because the top sheet, as its forward edge runs against the tapered face, slides down in the sheet feeding direction. The close position of the feed roller to the separation plate causes the face of the top sheet, while it is being fed, to be firmly in contact with the tapered face of the separation plate and thereby prevents the forward edge of the next sheet from going over the tapered face.

Description

[0001] The present invention relates to a sheet feeder for feeding sheets one by one, and more particularly to a sheet feeder capable of feeding not only ordinary paper sheets of A4 and B4 sizes but also relatively thick sheets such as postal cards or postcards.

[0002] Conventional sheet feeders for printers or facsimile apparatuses, which feed sheets of document or recording paper after separating them one by one, are classified into two types, one using a separation roller or a separation belt besides a feed roller and the other using separation claws provided on a hopper in which a plurality of sheets are stacked.

[0003] The former separates one of sheets stacked in a sheet tray by pressing front edges of the sheets with the separation roller which turns at low speed in the direction reverse to the feed roller, or by pressing the front edges with the separation belt having a high friction coefficient. However, as the thickness of sheets to be fed is considered in determining the position of the separation rollers or belt, variations of the thickness tends to invite sticking of two sheets (separation error) or jamming. Moreover, there is another disadvantage that stacking of many (for instance more than 30) sheets deteriorates the accuracy of sheet separation, and a configuration to prevent this deterioration is required.

[0004] On the other hand,the latter, the type of sheet feeder using a hopper provided with separation claws, will not be prevented from adequate separation even if many sheets are stacked in the hopper. FIG. 1 shows a perspective view of a part of such a sheet feeder, and FIG. 2, an A-A cross section of the sheet feeder of FIG. 1. In the diagrams, a plurality of sheets 50 are stacked in a hopper 25, and the top sheet is fed in the direction of arrow C by the rotation of feed rollers 21. The sheets 50 are pressed by a back-up plate 23 and springs 24 against the feed rollers 21, and in this state separation claws 22 hold the corners of the sheets 50. As the feed rollers 21 rotate to feed a sheet 50, the separation claws 22 restrain the forward edge of the sheet to curve the sheet as shown by the broken line in FIG. 2, and eventually the curved part is driven by the sheet's own firmness to go over the separation claws 22, resulting in the separation of that top sheet.

[0005] The sheet feeder illustrated in FIGS. 1 and 2, however, whose stability of separation is determined by the correlation between the sheet thickness and the square measure of the separation, claws 22 and accordingly is affected by a variation in sheet thickness, is unfit for the feeding of such thicker items as postcards and envelopes.

[0006] An object of the present invention, therefore, is to provide a sheet feeder which permits the stacking of a large number of sheets and moreover is capable of separating thicker items, such as postcards, one by one.

[0007] Another object of the invention is to provide a sheet feeder dispensing with such components as separation rollers, a separation belt and separation claws to hold the corners of sheets.

[0008] A sheet feeder according to the invention comprises a housing provided with a sheet accommodation space in which a plurality of sheets are to be stacked and held; a separation plate which is arranged against the forward edge of the sheets held in the housing and whose surface in contact with the forward edge of the sheets is substantially perpendicular to a sheet face; a feed roller, arranged close to the separation plate, for feeding the uppermost one of the sheets held in the housing in the forward direction while in contact with the face of that sheet; and pressurizing means for applying pressure to the sheets toward the feed roller. The separation plate has a tapered surface at its forward end included in the sheet feeding direction, so that the forward edge of the top sheet in contact with the feed roller runs against the tapered surface. This arrangement facilitates separation of the top sheet from the next even if the sheets are thicker than usual because the top sheet, as its forward edge runs against the tapered surface, slides down in the sheet feeding direction. In order to prevent two stuck sheets from being fed, it is desirable that the tapered face be included by 20 to 40 degrees along the sheet feeding direction against the surface with which the forward edge of the sheet comes into contact.

[0009] Further according to the present invention, the close position of the feed roller to the separation plate causes the face of the top sheet, while it is being fed, to be firmly in contact with the tapered face of the separation plate to push back the forward edge of the next sheet under the top sheet and thereby prevents the forward edge of the next sheet from going over the tapered face. More specifically, the center axis of the feed roller is positioned within 20 mm from the extension surface of said separation plate which contacts with the forward edge of the sheet in a direction perpendicular to that surface.

FIG. 1 shows a perspective view of a part of a sheet feeder according to the prior art;

FIG. 2 shows an A-A cross section of the sheet feeder of FIG. 1;

PIG. 3 shows an oblique view of a sheet feeder of the embodiment according to the present invention;

FIG. 4 shows a B-B cross section of the sheet feeder of FIG. 3;

FIG. 5 shows a cross section of the sheet feeder of FIG. 3 when sheets are accommodated;

FIG. 6 shows a perspective view of the sheet feeder of FIG. 3 with its rotating cover and guide removed;

FIG. 7 shows an oblique view of the rotating cover of the sheet feeder of FIG. 3;

FIG. 8 shows a cross-sectional view of the positional relation between the feed roller and the separation plate of the sheet feeder of FIG: 3; and

FIG. 9 shows a cross-sectional view of the sheet feeder, as illustrated in FIG. 4, when a plurality of sheets are accommodated therein.

[0010] FIG. 3 shows an oblique view of a sheet feeder which is a preferred embodiment of the present invention, and FIG. 4, a B-B cross section of the sheet feeder of FIG. 3. In the diagrams, a sheet feeder housing 100 consists of a frame 4, side plates 3A and 3B fixed to the two sides of the frame 4, a rotary cover 5 opposite to the rear face of the frame 4, and a guide 6. The rotary cover 5, provided at a sheet inlet 80, rotates 90 degrees around a rotational shaft 5A supported by the side plates 3A and 3B. The guide 6, arranged close to a sheet outlet, is fixed between the side plates 3A and 3B. At the top of the frame 4 is fixed a center guide 7 to support sheets.

[0011] FIG. 6 shows a perspective view of the sheet feeder of FIG. 3 with its cover 5 and guide 6 removed. In FIGS 6 and 4, a feed roller 1 is located inside the guide 6, and a shaft 1A around the center axis of the roller 1 is supported by the side plates 3A and 3B via bearings 2. The feed roller 1 should be built of a highly frictional material, preferably rubber. One end of the shaft 1A is fixed to a gear 12, which engages with a gear 13 turned by power supplied from a motor (not shown) to rotate the feed roller 1 in the direction of the arrow in FIG. 6. A plurality of sheets 50 are accommodated in a sheet accommodation space 8 among the rotary cover 5, guide 6 and frame 4. In that space are also arranged a pressurizing plate 9 and springs 10. One end of each spring 10 is fixed to the rear face of the frame 4, and the other end, to the pressurising plate 9, The pressurising plate 9 is always pressed against the feed roller 1 by the springs 10, and slides while keeping contact with the surface of a separation plate 11 fixed in the vicinity of an exit of the frame 4. The separation plate 11 is fixed in a direction perpendicular to the sheet face.

[0012] Referring to FIG. 5, as the rotary cover 5 turns 90 degrees around its center axis 5A, the tip of the rotary cover 5 causes the pressurizing plate 9 to escape into the inner part of the sheet accommodation space 8 against the elasticity of the springs 10. The rotary cover 5, as illustrated in FIG. 7, is provided on its two sides with pressing projections 61 and 62 for pressing the pressurizing plate 9, and the length M of these projections is substantially equal to the width of the sheet accommodation space 8. The plurality of sheets 50 are inserted through the sheet inlet 80, pass the sheet accommodation space 8 between the pressing projections 61 and 62, and run against the separation plate 11. After that, when the rotary cover 5 returns to its original position, the sheets 50 are pressed toward the feed roller 1 by the pressurizing plate 9. In this process, the rotary cover 5 performs the role of supporting the sheets 50.

[0013] Next will be described the positional relationship which is an essential element of the present invention, between the separation plate 11 and the feed roller 1, and the shape of the separation plate 11. Referring to FIG. 8, the center axis of the feed roller 1 is away from the extension surface P extending from the surface of the separation plate 11 which the forward edges of the sheets come into contact with, by a distance L in the veritcal direction. The distance L is set to be no more than 20 mm. This close position of the feed roller 1 to the separation plate 11 keeps the surface of the top sheet, while it is being fed, firmly in contact with a tapered face 11A, and thereby prevents the forward edge of the next sheet from going over the tapered face 11A. In this preferred embodiment, the distance L is 8 mm, the diameter of the feed roller 1, 10 mm, the height of the pressurizing plate 9 from the separation plate 11, 50 mm. The separation plate 11 has toward its end the tapered face 11A inclined in the direction of the sheet outlet. As illustrated in FIG. 8, the angle ϑ formed by the surface of the separation plate 11 and the tapered face 11A should desirably be 20 to 40 degrees. A greater angle ϑ than that would invite the feeding of two stuck sheets, or a smaller angle ϑ would cause the tapered face 11A stop the forward edge of the sheet to be separated and result in jamming.

[0014] Further referring to FIG. 8, the surface of the feed roller 1 is away by a distance N from a surface Q which is parallel to the sheet face and extends from the boundary between the tapered face 11A and the surface of the separation plate 11. The distance N is required for making it easier for the forward edge of the sheet in contact with the feed roller 1 to run against the tapered face 11A, and is 2.8 mm in this embodiment.

[0015] Thus, as the inclination angle ϑ of the tapered face 11A is 20 to 40 degrees and the forward edge of the top sheet runs against the tapered face 11A, thicker sheets such as postcards can be smoothly separated. Obviously, there is no trouble in separating sheets in the usual thickness range, such as A4 size plain paper sheets.

[0016] Power from the motor transmitted to the gear 13 (FIG. 3), after the plurality of sheets 50 have been placed in the sheet accommodation space 8 as shown in FIG. 9, turns the feed roller 1 via the gear 12. The top sheet in contact with the feed roller 1 is let out by the frictional force of the roller; its forward edge runs against the tapered face 11A of the separation plate 11; and the sheet, after being curved by the tapered face 11A, slides on. In this process, the top sheet comes into firm contact with the tapered face 11A while being fed by the feed roller 1 to create a force to push back the forward edge of the next sheet and thereby to ensure precise separation. The force of the pressurizing plate 9 to press the sheet 50 against the feed roller 1 also contributes to preventing the feed of two stuck sheets.

[0017] In this preferred embodiment, no material having a high friction coefficient is unfit for the separation plate 11, but a plastic or metallic material having a smooth surface is suitable. So that small sheets, such as postcards, can be accurately guided to the feed roller 1, movable sheet regulating guides may be provided at the sheet inlet 80. Furthermore, when the sheet feeder is fitted to a printer, the sheet feeder housing 100 will lose none of the sheet separating effect whether the rear face of the frame 4 is positioned horizontally or inclined.

Claims

1. A sheet feeder for separating and feeding a plurality of sheets one by one, comprising;
   a housing provided with a sheet accommodation space in which the plurality of sheets are to be stacked and held;
   a separation plate which is arranged against the forward edge of the sheets held in said housing and whose surface in contact with the forward edge of said sheets is substantially perpendicular to the faces of said sheets;
   a feed roller, arranged close to said separation plate, for feeding the uppermost one of the sheets held in said housing in the forward direction while in contact with the face of that sheet; and
   pressurizing means for applying pressure to said sheets toward said feed roller;
   wherein said separation plate has a tapered face at its forward end inclined in the sheet feeding direction, so that the forward edge of said top sheet run against the tapered face.

2. A sheet feeder, as claimed in Claim 1, wherein the center axis of said feed roller is positioned within 20 mm from the extension surface of said separation plate which comes into contact with said forward edge of the sheet in a direction perpendicular to that face, and said tapered face is inclined by 20 to 40 degrees along the sheet feeding direction against the surface with which the forward edge of said sheet comes into contact.

3. A sheet feeder, as claimed in Claim 2, wherein said pressurizing means has a pressurizing plate in contact with said sheet face and springs to press said pressurizing plate toward said feed roller.

4. A sheet feeder, as claimed in Claim 3, wherein said housing includes means to press said pressurizing plate in the direction to compress said springs and a space into which said pressuirzing plate being so pressed can escape from said sheet accommodation space.

5. A sheet feeder, as claimed in Claim 4, wherein said means to press said pressuirzing plate is a rotary cover supported by said housing.

Drawing