Sheet feeding or delivering – Feeding – Separators
Reexamination Certificate
2002-08-02
2003-11-18
Walsh, Donald P. (Department: 3653)
Sheet feeding or delivering
Feeding
Separators
C271S109000, C271S114000, C271S113000, C414S797300
Reexamination Certificate
active
06648322
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No. 2001-62535, filed Oct. 11, 2001, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a paper feeding device for a printer. More specifically, the present invention relates to a paper feeding device for a printer, in which an automatic compensation unit is provided.
2. Description of the Related Art
Generally, a printer is provided with a paper feeding device which is secured on the printer body, for feeding the paper sheets. The printer paper feeding device feeds paper sheets from a paper feeding cassette one by one into a printer body in accordance with printing signals. The paper feeding is achieved by exerting a vertical force on a rubber roller so as to generate a friction force between the paper sheet and the roller.
However, as the paper sheets are fed into the printer body and thus the stack of paper becomes lower, the vertical force varies, thereby varying the friction force as well. This hinders smooth paper feeding, thus the variation of the vertical force must remain within a certain range.
FIG. 1
schematically illustrates the construction of the conventional printer paper feeding device in which an automatic compensation unit is provided to compensate for the vertical forces.
FIG. 2
illustrates variations of paper contact angles of the paper feeding device of FIG.
1
. That is,
FIG. 2
illustrates an angle between an uppermost paper sheet of the paper stack at maximum height and the automatic compensation unit, and an angle between the lowermost paper sheet and the automatic compensation unit. Referring to
FIGS. 1 and 2
, the paper contact angles are varied from an angle &bgr;
1
(when the paper stack is at maximum height) to an angle &bgr;
2
(when only the last paper is left).
As shown in
FIG. 1
, the printer paper feeding device includes a pickup shaft
11
for transmitting the rotation torque of a driving source (not illustrated), an automatic compensation unit
10
provided with a pickup roller
15
, a paper feeding cassette
20
for accommodating a paper stack
30
, and a separating wall
23
formed on one end of the paper feeding cassette
20
in a paper-feeding direction, for separating the paper sheets.
The automatic compensation unit
10
comprises a train of four gears
13
a,
13
b,
13
c
and
13
d.
The train of four gears
13
a,
13
b,
13
c
and
13
d
are pivotally connected to the pickup shaft
11
so that the first gear
13
a
can transmit the rotation torque T of the pickup shaft
11
to the pickup roller
15
, and the pickup roller
15
can vary its contact position on the paper stack
30
as the height of the paper stack
30
is decreased during the printing operation. The pickup roller
15
is coupled coaxially to a shaft of the 4th gear
13
d
by being interlocked to the pickup shaft
11
.
The operation of the printer paper feeding device will now be described. When the pickup shaft
11
is rotated by the driving source (not illustrated), then the first gear
13
a
rotates, and the second and third gears
13
b
and
13
c
rotate so as to ultimately transmit the power to the fourth gear
13
d.
The pickup roller
15
is assembled to the shaft of the fourth gear
13
d,
and therefore, if the fourth gear
13
d
rotates, then the pickup roller
15
also rotates. If the pickup roller
15
rotates, the uppermost sheets of paper of the cassette
20
are biased forward due to the friction force between the pickup roller
15
and the paper stack
30
. Then, due to the presence of the separating wall
23
, only the uppermost sheet of paper is separated and fed into the printer body.
If the paper sheets are to be separated one by one, the following conditions must be satisfied:
F
pick
>F
fric
>F
d
>F
double
<Formula 1>
where F
pick
is the feeding force due to the rotation torque of the pickup roller
15
, F
fric
is the carrying force due to the friction between the pickup roller
15
and the paper stack
30
, F
d
is the resistant force acting on the leading edge of the paper by the separating wall
23
and F
double
is the carrying force for the second sheet paper next to the uppermost paper sheet.
First, F
pick
is calculated as follows:
F
pick
=T/r
<Formula 2>
where T is the rotation torque of the pickup shaft
11
and r is the radius of the pickup roller
15
, F
fric
is calculated as follows:
F
fric
=&mgr;
roll
×N
total
<Formula 3>
where &mgr;
roll
is the friction coefficient between the paper stack
30
and the pickup roller
15
and N
total
is the maximum vertical force pressing on the paper stack
30
by the pickup roller
15
.
Finally, F
double
is calculated as follows:
F
double
=&mgr;
paper
×N
total
<Formula 4>
where &mgr;
paper
is the friction coefficient between the paper sheets, and N
total
is the maximum vertical force pressing on the paper stack
30
by the pickup roller
15
.
As shown in Formulas 2 through 4, if factors such as the rotation torque T of the pickup shaft
11
, the radius r of the pickup roller
15
, the separating wall
23
and the type of paper sheet are properly chosen, then F
pick
and F
d
become constant regardless of a height h of the paper stack
30
, and therefore, the height h is constant. However, F
fric
and F
double
vary in accordance with the height of the paper stack
30
, and therefore, F
fric
and F
double
are treated as variables. Accordingly, whether Formula 1 is satisfied or not is determined by the value of N
total
.
N
total
is the vertical force pressing on the paper stack
30
by the pickup roller
15
, and therefore, it can be expressed as the vertical force acting on the pickup roller
15
. N
total
is the sum total of: a vertical force N
R
due to the rotation torque of the pickup roller
15
, a vertical force N
A
due to a link
12
of the automatic compensation unit
10
, and a vertical force N
W
due to the weight of the automatic compensation unit
10
.
N
total
=N
R
+N
A
+N
W
<Formula 5>
In the above formula, the vertical force N
R
acts such that the rotation torque of the pickup roller
15
increases the vertical force N
R
at the instant when F
d
>F
fric
so as to stop the feeding of the paper sheets. Referring to
FIG. 3A
, a maximum value of the vertical force N
R
is calculated by the following formula.
N
R
=
T
r
·
cos
β
·
sin
β
<Formula 6>
where T is the rotation torque of the pickup roller
15
, r is the radius of the pickup roller
15
, and &bgr; is the paper contact angle.
Further, the vertical force N
A
due to the action of the link
12
of the automatic compensation unit is generated when the carrying force F
fric
due to the pickup roller
15
attains equilibrium with the paper feed resistance F
d
to stop the rotation of the pickup roller
15
. A maximum value of the vertical force N
A
is calculated based on the following formula by referring to FIG.
3
B.
N
A
=
T
L
·
cos
β
<Formula 7>
where L is the length of the link
12
of the automatic compensation unit
10
, T is the rotation torque of the pickup roller
15
, and &bgr; is the paper contact angle.
The vertical force N
W
due to the weight of the automatic compensation unit 10 is calculated based on the following formula by referring to FIG.
3
C.
N
W
=
W
·
D
L
<Formula 8>
where W is the total weight of the automatic compensation unit
10
, D is the distance from the center of the first gear
13
a
to the center of gravity of the automatic compensation unit
10
, and L is the length of the link
12
of the automatic compensation unit
10
.
Accordingly, if Formulas 6 through 8 are substituted into Formula 5, then Formula 5 can be expressed as follows:
N
total
=
T
r
·
sin
&emsp
Joerger Kaitlin S
Samsung Electronics Co,. Ltd.
Staas & Halsey , LLP
Walsh Donald P.
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