Sheet feeding or delivering – Feeding – Separators
Reexamination Certificate
2001-08-08
2004-11-30
Walsh, Donald P. (Department: 3653)
Sheet feeding or delivering
Feeding
Separators
C271S124000, C271S127000
Reexamination Certificate
active
06824131
ABSTRACT:
BACKGROUND
1. Field of the Invention
This patent specification relates to a method and apparatus for image forming, and more particularly to a method and apparatus for image forming and effectively performing a sheet transfer.
2. Description of Related Art
Conventionally, sheet feeders for separating stacked sheet materials one by one to feed them from the topmost one are classified into a corner tab separation type which presses both ends in the width direction on the leading edge of a sheet material in a feeding direction with tab members for separation; a separation pad type which urges a friction member to separate a sheet material; a bank separation type which runs sheet materials into a fixed gate member having a slope for separating the sheet materials one by one; and so on.
Among these types of sheet feeders, the known separation pad type sheet feeder, or the bank separation type sheet feeder discussed, for example, in Laid-open Japanese Patent Application No. 8-91612 are preferred since they require a low number of parts, but can be applied to a variety of different sheet materials (for example, post cards, envelopes, OHP (over head projector) sheets and so on) of different sizes including thick and thin materials in the same configuration at a low cost.
However, a conventional sheet feeder of the separation pad type generates noise due to friction slip, when a sheet material is being conveyed, sandwiched between a sheet feed roller and a friction member, particularly in a low cost, low speed machine operating 10 PPM (an image forming speed of 10 sheets per minute) or less. To prevent such noise, it is necessary to form the sheet feed roller in a semilunar shape. This leads to a requirement of a pair of cylindrical collars each having a diameter slightly smaller than that of the sheet feed roller additionally disposed coaxially with the sheet feed roller on both sides thereof for preventing a sheet stack stacking member from lifting up. Consequently, the number of parts is increased to result in a higher cost.
Recently, as recycled paper is increasingly used, sheet materials such as post cards and envelopes often having burred leading edges in a conveying direction, possibly produced in a cutting operation, cause an extra conveying load, so that the separation pad type sheet feeder can fail to feed sheet materials.
Further, back sides of once used sheet materials are also increasingly used, in which case stacked sheet materials differ in friction coefficient from one another so that two or more sheet materials may be fed at one time. A once used sheet material may be curled during fixation depending on a particular environment. Thus, a sheet material separator may be burdened with a greater load due to a curled leading edge of a sheet material depending on a direction in which the sheet material is curled, and may fail to separate the sheet materials for conveying them one by one.
It should be noted that the separation pad type sheet feeder presses a plane portion of a pad onto a sheet feed roller, so that the angle of a separation pad to a direction in which a sheet material fed from a stack is conveyed (corresponding to a displacement angle of a sheet material stacking member such as a bottom board) must be limited within a predetermined range. To conform to this limitation, the sheet feed roller is also limited in diameter, and the degree of freedom in layout is also restricted, thereby giving rise to a problem that the sheet feeder cannot be reduced in size.
On the other hand, the bank separation type sheet feeder discussed in Laid-open Japanese Patent Application No. 8-91612 includes a tilt member in contact with a sheet feed roller, which has a flat upper edge and a wide nip region with the sheet feed roller, so that variations in the member or the like can make it difficult to arrange the tilt face at a predetermined tilt angle.
When the topmost sheet material is being conveyed in an image forming unit, the sheet feed roller generally is not driven by the mechanism that rotates it to feed a sheet from the stack. However, while a previous sheet material is nipped between the sheet feed roller and a gate member, the sheet feed roller is rotated due to the friction force with the sheet material, and as the trailing edge of the previous sheet material passes the nip region, the leading edge of the next sheet material is sent to the tilt member by the associated rotation of the sheet feed roller.
In this event, if a friction coefficient between sheet materials is high or varies greatly, and the friction coefficient between the previous sheet material and the next sheet material is lower than the friction coefficient between the next sheet material and the sheet material subsequent to the next sheet material, the next sheet material can go beyond the tilt member to result in multiple sheet feeding.
Generally, in a sheet feeder which removably supports, through an opening of the feeder body, a cassette having a sheet material stacking member which has one end supported for pivotal movement and a free end urged upward, a tilt member and a sheet material separator in pressing contact with a sheet feed roller are positioned deep in the feeder body. Therefore, if a user attempts to draw out the cassette which contains few sheet materials, the sheet material stacking member may be caught in the feeder body, to keep the user from drawing out the cassette.
To overcome such a problem, as illustrated in
FIG. 54
, a conventionally known sheet feeder has a pair of protruding arms
1
c
(only one of which is shown in
FIG. 54
) integrally arranged on both sides of a bottom board
1
, which is a sheet material stacking member having one end supported by a shaft
1
a
for pivotal movement within a cassette
11
and a free end urged upward at all times by a compression spring
3
, and guide rails
10
c
formed on a feeder body
10
corresponding to the arms
1
c,
such that as the cassette
11
is drawn in a direction indicated by an arrow Y, the arms
1
c
come in contact with the guide rails
10
c
and lower the bottom board
1
against an urging force of the compression spring
3
as illustrated in
FIG. 55
, and the bottom board
1
is held at the lowered position by a known stopper means when the cassette
11
is drawn out.
However, although such a sheet feeder can prevent the bottom board
1
from being caught when the cassette
11
is drawn out, the tilt member is pressed onto the sheet feed roller
4
by the compression spring
5
after a sheet material has been fed before the cassette
11
is drawn out, so that the leading edge of the next sheet material
2
n
may remain nipped by the sheet feed roller
4
after the previous sheet has been fed (see FIG.
55
).
If the cassette
11
is drawn out to supply sheet materials and again set in the sheet feeder, a remaining sheet material
2
n
within the feeder body
10
is crushed by the set cassette
11
to block the separator comprised of the tilt member
6
, resulting in an inability of the sheet feeder to feed sheet materials.
To solve this problem, a conventional sheet feeder includes means associated with a movement of a drawn cassette to release the pressure of the tilt member. Another conventional sheet feeder provides a cassette with a separate arm for raking out the leading edge of a nipped sheet material. A further conventional sheet feeder senses a movement of a drawn cassette to rotate the sheet feed roller in a direction reverse to a sheet feeding direction to remove the leading edge of a sheet material from a nip region.
Among these conventional techniques, the first and third sheet feeders require an increased number of parts and increased steps for assembly to introduce a lower production efficiency. The second sheet feeder, on the other hand, can cause sheet material to tear and remain near the nip region, depending on the material, since the arm attempts to rake out the sheet material, as it is, nipped by a pressure applied by the tilt member and a pressure applied by the leading edge of the bottom board.
Furt
Cooper & Dunham LLP
Ricoh & Company, Ltd.
Schlak Daniel K
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