Sheet feeding or delivering – Feeding – Multiple supplies
Reexamination Certificate
2001-01-29
2002-10-22
Skaggs, H. Grant (Department: 3653)
Sheet feeding or delivering
Feeding
Multiple supplies
C271S117000
Reexamination Certificate
active
06467765
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet feeding apparatus and an image forming apparatus having such a sheet feeding apparatus, and more particularly, it relates to a sheet feeding apparatus in which a sheet is fed out by sheet feeding means provided above the sheet for lifting and lowering movements.
2. Related Background Art
In some of conventional image forming apparatuses such as printers, copying machines and the like, there is provided a sheet feeding apparatus in which a sheet is fed to an image forming portion by sheet feeding means such as a pick-up roller. Among such sheet feeding apparatuses, there is a sheet feeding apparatus in which the sheet feeding means is provided above the sheet for lifting and lowering movements in such a manner that, when the sheet is fed, the sheet feeding means is lowered to be urged against the sheet and, in this condition, the sheet is fed out by rotating the sheet feeding means, and, thereafter, the sheet feeding means is lifted to be separated from the sheet.
By the way, in such a sheet feeding apparatus, although means for lifting and lowering the sheet feeding means was generally comprised of a solenoid or a cam one revolution of which is controlled, recently, as the speed of the printer has been increased, it is required that the sheet feeding means be urged against the sheet at higher speed and also be separated from the sheet at higher speed after the feeding of the sheet. Further, as noise of recent printers has been reduced, it is required for avoiding usage of an actuator such as a solenoid generating great noise.
To this end, there has been proposed a sheet feeding apparatus in which, as the means for lifting and lowering the sheet feeding means, a lifting and lowering mechanism for directly lifting and lowering the sheet feeding means by using a pulse motor, for example, is provided.
FIG. 8
shows a construction of such a conventional sheet feeding apparatus using a pulse motor. In
FIG. 8
, the sheet feeding apparatus comprises pick-up rollers
1
a
,
1
b
as sheet feeding means provided for lifting and lowering movements, and rotations of the pick-up rollers around shafts
2
a
,
2
b
are controlled by drive sources (not shown). Further, the pick-up rollers
1
a
,
1
b
are rotatably held on ends of roller holders
3
a
,
3
b
which are held by an image forming apparatus (not shown) for rotations around shafts
4
a
,
4
b.
Incidentally, there are provided roller springs
5
a
,
5
b
as urging means for biasing the pick-up rollers
1
a
,
1
b
in anti-clockwise directions (along which the rollers are urged against an upper surface of a stached sheet P) via the roller holders
3
a
,
3
b
so that the pick-up rollers
1
a
,
1
b
are urged against the sheet (not shown) with predetermined pressure by biasing the pickup rollers
1
a
,
1
b
in the anti-clockwise directions by means of the roller springs
5
a
,
5
b.
Further, in
FIG. 8
, the reference numeral
6
denotes a rod as a holding member capable of moving in an up-and-down direction and adapted to hold the pick-up rollers
1
a
,
1
b
for lifting and lowering movements, and “M” denotes a pulse motor as a reversible motor. Rotation of the pulse motor M is transmitted to the rod
6
via a motor gear
12
, a first drive transmitting gear
11
as a first transmitting gear meshed with the motor gear
12
, a second drive transmitting gear
13
as a second transmitting gear integrally formed with the first drive transmitting gear
11
, and a rack gear
10
meshed with the second drive transmitting gear
13
and provided on one side of the rod
6
. Incidentally, the first and second drive transmitting gears
11
,
13
are rotatably held on a rotary shaft
17
.
On the other hand, guide holes
6
c
extending in an up-and-down direction are formed in upper and lower portions of the rod
6
, so that, when the rotation of the pulse motor M is transmitted via the gear train comprised of the motor gear
12
, first and second drive transmitting gears
11
,
13
and rack gear
10
, the rod
6
is shifted in the up-and-down direction while being guided by pins
7
,
8
inserted in the guide holes
6
c.
Incidentally, support portions
6
a
,
6
b
for supporting the shafts
2
a
,
2
b
of the pick-up rollers
1
a
,
1
b
from below are protruded horizontally from lower and upper ends of the rod
6
. With this arrangement, when the rod
6
is shifted in the up-and-down direction, the pick-up rollers
1
a
,
1
b
are shifted in the up-and-down direction by the aid of the spring forces of the roller springs
5
a
,
5
b
or in opposition to the spring forces as the rod
6
is shifted.
Next, a sheet feeding operation of the sheet feeding apparatus having the above-mentioned construction will be explained.
In a waiting condition of the sheet feeding apparatus before it starts the sheet feeding operation, the rod
6
is held at a highest position or home position, so that the pick-up rollers
1
a
,
1
b
are positioned above the sheet. In this case, although the pulse motor M is not rotated, it is maintained in an exciting condition so that the rod
6
is held in the home position in opposition to the biasing forces of the roller springs
5
a
,
5
b.
On the other hand, when sheet feeding command is emitted from a controlling device (not shown) provided in the image forming apparatus, first of all, the pulse motor M is rotated in the anti-clockwise direction, and the anti-clockwise rotation is transmitted to the rod
6
via the motor gear
12
, first and second drive transmitting gears
11
,
13
and rack gear
10
, with the result that the rod
6
is lowered. When the rod
6
is lowered in this way, the pick-up rollers
1
a
,
1
b
are also lowered together with the rod
6
by the biasing forces of the roller springs
5
a
,
5
b
, thereby urging the pick-up rollers against the sheet P.
Incidentally, even after the pick-up rollers
1
a
,
1
b
are urged against the sheet in this way, the rod
6
is further lowered by a predetermined distance. Here, when the rod
6
is lowered in this way, since the pick-up rollers
1
a
,
1
b
abut against the sheet, the support portions
6
a
,
6
b
of the rod
6
are separated from the shafts
2
a
,
2
b
of the pick-up rollers
1
a
,
1
b
. As a result, the pick-up rollers
1
a
,
1
b
are urged against the sheet P with predetermined abut pressure by the biasing forces of the roller springs
5
a
,
5
b.
After the pick-up rollers
1
a
,
1
b
are urged against the sheet P in this way, by rotating the pick-up rollers
1
a
,
1
b
, the sheet P can be fed to the image forming portion (not shown).
On the other hand, when the sheet feeding operation is finished, the pulse motor M is rotated in a clockwise direction, with the result that the rod
6
is lifted and the support portions
6
a
,
6
b
abut against the shafts
2
a
,
2
b
of the pick-up rollers
1
a
,
1
b
from below. Further, thereafter, when the rod
6
is lifted, the pick-up rollers
1
a
,
1
b
are lifted together with the rod
6
in opposition to the biasing forces of the roller springs
5
a
,
5
b
, thereby separating the pick-up rollers from the sheet P. Thereafter, the rod
6
is returned to the home position. In this case, by bringing the pulse motor M to the exciting condition, the rod
6
is held at the home position in opposition to the biasing forces of the roller springs
5
a
,
5
b.
By the way, the during such a sheet feeding operation, since the pick-up rollers
1
a
,
1
b
are biased so that they generally abut against the sheet P with load in the order of about 0.5 N to about 3 N, when the above-mentioned sheet feeding operation is effected, torque acting on the pulse motor M is changed as shown in FIG.
9
. Incidentally, in
FIG. 9
, the ordinate indicates the position of the rod
6
and the abscissa indicates torque acting on the motor shaft of the pulse motor M.
As apparent from
FIG. 9
, when the rod
6
is in the home position, maximum torque T
max
acts on the pulse motor M to hold the rod
6
in the home position. Furt
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Skaggs H. Grant
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