Sheet feeder

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a sheet feeder in which individual sheets are separately fed by a sheet feed roller.

2. Description of Related Art

A sheet feeder that feeds sheets to a printer, such as an ink-jet printer and a laser printer, typically includes a sheet feed cassette for storing a stack of sheets to be printed, a vertically movable pressure plate disposed at the bottom of the sheet feed cassette to support thereon the sheets, a sheet feed roller for feeding the sheets from the pressure plate, a push plate for moving up the pressure plate and bringing the sheets on the pressure plate into contact with the sheet feed roller, and a separation pad for separating a single sheet from the stack in contact with the sheet feed roller.

In a printer having such a sheet feeder, when a single sheet is separated from the stack, the pressure plate is moved up by the push plate toward the sheet feed roller and the stack on the pressure plate is brought into contact with the sheet feed roller with an optimum pressure. After that, when the sheet feed roller rotates, a single sheet is separated from the stack by the sheet feed roller and the separation pad.

On the other hand, when the separated sheet is conveyed, the push plate is lowered toward the bottom of the sheet feed cassette, and the pressure plate is also lowered to the bottom of sheet feed cassette. When the pressure plate is lowered, the stack on the pressure plate is apart from the sheet feed roller. This prevents the remaining sheets from being pressed against the sheet feed roller by the pressure plate. Accordingly, the next sheet beneath the separated sheet is prevented from being conveyed together with the seperated sheet. In addition, the rotation load of the sheet feed roller is reduced.

After that, when a sheet feed command is issued from a controller, the pressure plate is moved up by the push plate from the bottom of the sheet feed cassette toward the sheet feed roller, and the next sheet stacked on the pressure plate is brought into contact with the sheet feed roller. Then, the next sheet starts being conveyed.

In the above-described sheet feeder, when the sheet separated by the sheet feed roller and the separation pad is conveyed, the pressure plate should be lowered to the bottom of the sheet feed cassette by lowering the push plate from the upper position where the stack is in contact with the sheet feed roller to the lower position where the stack is away from the sheet feed roller.

After that, when the next sheet is separated, the push plate should be raised again from the lower position to the upper position to bring the next sheet stacked on the pressure plate into contact with the sheet feed roller.

In this way, when the pressure plate is moved up from the bottom of the sheet feed cassette toward the sheet feed roller by moving up the push plate from the lower position to the upper position, the moving distance of the pressure plate is so long that high impact noise is generated upon the contact between the sheets stacked on the pressure plate and the sheet feed roller. As a result, considerable noise is produced during the operation of the sheet feeder.

In order to separately feed a single sheet, the push plate that pushes the pressure plate should be vertically moved from the position where the sheets are in contact with the sheet feed roller and the position where the sheets are away from the sheet feed roller. Thus, another problem arises in that it takes a long time to separately feed a single sheet and, as a result, the sheet feed speed of the sheet feeder becomes low. To overcome this problem and to move the push plate at high speed, use of a high torque drive motor is conceivable. However, such a motor is expensive and results in an increase in the total production cost of the sheet feeder.

SUMMARY OF THE INVENTION

In view of the foregoing problems, one aspect of the invention is to provide a sheet feeder that generates low impact noise when a sheet support member is vertically moved by a pushing member, uses a low-powered lowering mechanism to lower the pushing member, and can reduce the sheet feed time per sheet to increase the sheet feed speed.

A sheet feeder according to the invention may include a sheet support member that supports thereon a stack of sheets, a sheet feed roller that is rotatably disposed above one end of the sheet support member and separates a single sheet from the stack of sheets and then conveys the separated single sheet, a pushing member that is vertically movable and pushes the sheet support member toward the sheet feed roller between a lower position where the stack of sheets is away from the sheet feed roller and an upper position where the stack of sheets is in contact with the sheet feed roller, an urging member that urges the pushing member from the lower position to the upper position, a lowering device that lowers the pushing member urged by the urging member by a predetermined distance from the upper position when the sheet feed roller conveys the separated single sheet, a halting device that halts the pushing member lowered by the lowering device at a position lower than the upper position and higher than the lower position, and a halt release device that releases the halted pushing member.

In the sheet feeder as structured above, a stack of sheets is put on the sheet support member when the pushing member is at the lower position. Thus, the stack on the sheet support member is away from the sheet feed roller. After that, the pushing member is urged from the lower position to the upper position and moved up toward the upper position. When the pushing member reaches the upper position, the stack on the sheet support member is brought into contact with the sheet feed roller. Then, a single sheet is separated from the stack in contact with the sheet feed roller as the sheet feed roller rotates.

After the single sheet is separated, the pushing member is lowered by the predetermined distance by the lowering device and halted by the halting device at a position lower than the upper position and higher than the lower position. The stack on the sheet support member falls away by the predetermined distance from the sheet feed roller. Thus, the separated sheet is conveyed by the sheet feed roller without being pressed by the sheet support member pushed by the pushing member against the sheet feed roller.

After the sheet is conveyed by the sheet feed roller, the halt release device releases the pushing device halted by the halting device. The pushing device is urged from the halted position toward the upper position by an urging force of the urging member. Thereby, the pushing member returns again to the upper position, and the sheet support member is pushed up toward the sheet feed roller. The next sheet of the stack is brought into contact with the sheet feed roller so as to be separated and conveyed.

The lowering device of the sheet feeder may include a ratchet gear having, on its outer circumference, a plurality of engaging pawls and rotated in a forward direction during upward movement of the pushing member toward the upper position and rotated in a reverse direction, which is opposite to the forward direction, during downward movement of the pushing member toward the lower position, a first cam member rotated as the sheet feed roller rotates, an actuating member projecting toward the first cam member and pushed by the first cam member as the sheet feed roller rotates, and an engaging member that, when the actuating member is pushed by the first cam member, engages one of the engaging pawls and swings in a same direction as the reverse rotation direction of the ratchet gear so as to rotate the ratchet gear by a predetermined angle in the reverse direction.

In the lowering device as structured above, the first cam member is rotated as the sheet feed roller rotates. The actuating member is moved by the rotation of the first cam member toward a certain direction such that the engaging member engages with one of the engaging pawls of the ratchet gear. When the actuating member is further moved by the first cam member, the engaging member swings in the same direction as the reverse rotation direction of the ratchet gear. Simultaneously, the ratchet gear is rotated in the reverse direction. Thereby, the pushing member is lowered by the predetermined distance toward the lower position.

Further, the first cam member is structured to release the actuating member when the ratchet gear has been rotated by the predetermined angle in the reverse direction and, upon release of the actuating member by the first cam member, the engaging member is released by one of the engaging pawls.

When the ratchet gear has been rotated by the engaging member by a predetermined angle, the actuating member is released by the first cam member, and thereby the engaging member is disengaged from one of the engaging pawls of the ratchet gear. This disengagement prevents the ratchet gear from rotating excessively in the reverse direction and the pushing member from being lowered more than the predetermined distance.

Further, the halting device of the sheet feeder may include a locking member that is engageable with one of the engaging pawls and, when engaged with one of the engaging pawls, restricts the forward rotation of the ratchet gear while permitting the reverse rotation of the ratchet gear.

Accordingly, the engagement of the locking member with one of the engaging pawls restricts the forward rotation of the ratchet gear. This restriction prevents the pushing member from moving up and halts the pushing member at the position lowered by the predetermined distance from the upper position. In addition, the locking member, when engaged with one of the engaging pawls, permits the reverse rotation of the ratchet gear. Thus, the locking member allows the pushing member to be lowered by the reverse rotation of the ratchet gear, while restricting the forward rotation of the ratchet gear and preventing the upward movement of the pushing member.

Further, the halt release device of the sheet feeder may include a second cam member that is rotated as the sheet feed roller rotates and pushes the locking member so as to release engagement between the locking member and one of the engaging pawls.

Accordingly, the engaging member, when pushed down by the second cam member, is disengaged from one of the engaging pawls. This disengagement allows the ratchet gear to rotate in the forward direction and the pushing member to move up toward the upper position. The pushing member is urged toward the upper position. The ratchet gear is rotated in the forward direction by this urging force and, in response to the rotation, the pushing member returns to the upper position.

The sheet feeder may further include an attenuator that attenuates the moving speed of the pushing member when the pushing member is moved upward by an urging force of the urging member.

Accordingly, impact of a stack of sheets on the sheet support member with the sheet feed roller is reduced. Because the stack on the sheet support member is prevented from colliding violently with the sheet feed roller, impact noise generated during upward movement of the push plate

24

is reduced.

The sheet feeder may further include a case and a sheet feed cassette detachably attached to the case and provided with the sheet support member. The sheet feed cassette may include an urging force starting member that makes the urging member start generating an urging force.

When the sheet feed cassette is attached to the case, the urging force starting member makes the urging member start generating an urging force. The generated urging force makes the pushing member move up toward the upper position.

Still further, the urging member of the sheet feeder may be made of an elastic material.

Accordingly, no electric device, such as a motor, is required, as an urging force generating device, to urge the pushing member. Thus, the total production cost of the sheet feeder can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will be described in detail with reference to the following figures wherein:

FIG. 1

is a side sectional view showing the internal structure of a printer having a sheet feeder as one embodiment of the invention, where a push plate is at its lower position;

FIG. 2

is an external perspective view of a sheet feed cassette and a cassette cover;

FIG. 3

is a front view of a pushing device;

FIG. 4

is a right side sectional view of the pushing device of

FIG. 3

;

FIG. 5

is a side sectional view taken along line V—V of

FIG. 3

;

FIG. 6

is a side sectional view taken along line VI—VI of

FIG. 3

;

FIG. 7

is a side sectional view of a lowering mechanism;

FIG. 8

is a side sectional view taken along line VII—VII of

FIG. 3

;

FIG. 9

is a side sectional view showing the internal structure of the printer, with a push plate at its upper position; and

FIG. 10

is a side sectional view showing the internal structure of the printer, with the push plate at its standby position.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A preferred embodiment of the invention will now be described with reference to the attached figures.

FIG. 1

is a sectional view showing the internal structure of a printer (image forming device)

1

having a sheet feeder

2

as an embodiment of the invention and also schematically showing a pushing device

20

, which will be described later. In

FIG. 1

, the push plate

24

is at its lower position.

Arrows shown in

FIG. 1

indicate particular directions. Arrow A indicates the direction in which a sheet feed cassette

4

is inserted into a cassette inserting section

1

b

. Arrow X

1

indicates the sheet feed direction in which a sheet P to be printed is fed into a sheet feed port

2

a

. Arrow X

2

indicates the sheet discharge direction in which a sheet P is discharged onto a cassette cover

5

. Arrow X

3

indicates the direction in which a sheet P to be printed is manually fed from the cassette cover

5

.

The printer

1

is a so-called ink-jet printer and includes a sheet feeder

2

for feeding sheets P individually and a printing device

3

for printing an image on a sheet P. In the printer

1

, the sheet feeder

2

and the printing device

3

are housed in a main case

1

a

, which is box-shaped and made of a synthetic resin.

The sheet feeder

2

has an automatic sheet feed function for feeding an individual sheet from a stack of sheets P in the sheet feed cassette

4

, and a manual sheet feed function for feeding sheets P that are manually inserted from a manual sheet feed port

5

d

of the cassette cover

5

. The sheet feeder

2

has the sheet feed port

2

a

into which a new sheet P is fed, and a sheet discharge port

2

b

through which a sheet P fed into the sheet feed port

2

a

is discharged to the outside of the main case

1

a.

The sheet feed cassette

4

is disposed upstream (on the right side in

FIG. 1

) of the sheet feed port

2

a

of the sheet feeder

2

and stores a stack of new sheets P. The sheet feed cassette

4

is detachably inserted into the cassette inserting section

1

b

at a lower portion of the main case

1

a.

The sheet feed cassette

4

is a shallow, hollow box having an open top surface (hereinafter referred to simply as an “open surface”). The cassette cover

5

is detachably attached to the open surface on the side (right side in

FIG. 1

) away from the sheet feed port

2

a

. Thus, the sheet feed cassette

4

has a covered portion

4

a

where the open surface on the side (right side in

FIG. 1

) away from the sheet feed port

2

a

is covered, and an uncovered portion

4

b

where the open surface on the side (left side in

FIG. 1

) near the sheet feed port

2

a

remains open.

A flat bottom plate

4

c

is provided internally at the bottom of the sheet feed cassette

4

. A flat pressure plate

6

is provided internally on the bottom plate

4

c

in the longitudinal direction (rightward/leftward direction in

FIG. 1

) of the sheet feed cassette

4

.

The cassette cover

5

is provided to cover the open surface of the covered portion

4

a

of the sheet feed cassette

4

. The cassette cover

5

has a sheet edge-receiving portion

5

a

that receives the trailing edge side (on the left side in

FIG. 1

) of a sheet P discharged (in the direction of arrow X

2

in

FIG. 1

) from the sheet discharge port

2

b

, and a flat sheet-holding portion

5

b

that holds the leading edge side of a discharged sheet P.

The sheet edge-receiving portion

5

a

extends from the lower portion of the sheet discharge port

2

b

while being tilted down toward the sheet discharge direction (indicated by arrow X

2

in FIG.

1

). On the other hand, the sheet-holding portion

5

b

extends substantially horizontally from the lower end of the sheet edge-receiving portion

5

a

, that is, from the end (on the right side in

FIG.1

) thereof opposite to the sheet discharge port

2

b

, toward the sheet discharge direction (indicated by arrow X

2

in FIG.

1

).

Thus, the cassette cover

5

holds a sheet P discharged from the sheet discharge port

2

b

such that its trailing edge (on the left side in

FIG. 1

) received by the sheet edge-receiving portion

5

a

is tilted up toward the sheet discharge port

2

b.

A communicating space

2

c

that communicates with the sheet feed port

2

a

is defined below the sheet edge-receiving section, that is, between the lower surface of the sheet-edge receiving portion

5

a

and the upper surface of a stack of sheets in the sheet feed cassette

4

. The communication space

2

c

allows a sheet P manually fed from the cassette cover

5

to be guided therethrough to the sheet feed port

2

a.

A substantially flat partition

5

c

is vertically provided above the communicating space

2

c

, on the upper end of the sheet-edge receiving portion

5

a

, that is, on the end (on the left side in

FIG. 1

) near the sheet discharge port

2

b

. The partition

5

c

is provided to separate the communicating space

2

c

from the space above the sheet edge-receiving portion

5

a

(cassette cover

5

).

Accordingly, sheets P discharged from the print discharge port

2

b

are prevented by the partition

5

c

from slipping down from the upper end of the sheet edge-receiving portion

5

a

to the communicating space

2

c

. In other words, printed sheets P are prevented from entering the communicating space

2

c

and from being supplied again into the sheet feed port

2

a

. In addition, the cassette cover

5

holds sheets P discharged from the sheet discharge port

2

b

with their trailing edges (on the left side in

FIG. 1

) tilted up toward the sheet discharge port

2

b

, thereby preventing the discharged sheets P from crossing over the partition

5

c

and entering the communicating space

2

c.

The manual sheet feed port

5

d

is provided wide open at a substantially central part of the tilted sheet edge-receiving portion

5

a

, substantially perpendicularly to the tilted direction. The manual sheet feed port

5

d

allows a new sheet P to be manually inserted from the cassette cover

5

. Also, the manual sheet feed port

5

d

allows the space above the sheet edge-receiving portion

5

a

(cassette cover

5

) to communicate with the communicating space

2

c

. Thus, a sheet manually inserted from the upper side of the sheet edge-receiving portion

5

a

enters the communicating space

2

c

below the sheet edge-receiving portion and passes therethrough to the sheet feed port

2

a.

The manual sheet feed port

5

d

is provided on the tilted-down side of the sheet edge-receiving portion

5

a

with respect to the trailing edges (on the left side in

FIG. 1

) of discharged sheets P held by the sheet edge-receiving portion

5

a

. Thus, the trailing edges of sheets P discharged from the sheet discharge port

2

b

are prevented from mistakenly entering the manual sheet feed port

5

d

. In addition, the sheet edge-receiving portion

5

a

holds the discharged sheets P with their trailing edges (on the left side in

FIG. 1

) tilted up toward the sheet discharge port

2

b

, so that the trailing edges hardly enter the manual sheet feed port

5

d.

The pressure plate

6

supports thereon a stack of sheets P stored in the sheet feed cassette

4

. A pivot shaft

6

a

is provided on a longitudinal side (on the right side in

FIG. 1

) of the pressure plate

6

. The pivot shaft

6

a

is rotatably supported by the sheet feed cassette

4

. The pressure plate

6

is supported by the pivot shaft

6

a

so as to vertically swing about the pivot shaft

6

a.

The pushing device

20

is disposed on the opposite side (on the left side in

FIG. 1

) of the pressure plate

6

from the pivot shaft

6

a

. The pushing device

20

has a push plate

24

that moves up the pressure plate

6

. The right edge (

FIG. 1

) of the push plate

24

makes contact with the lower surface of the pressure plate

6

. As the push plate

24

moves up, the pressure plate

6

swings upward about the pivot shaft

6

a

so that the sheets P supported thereon make contact with the lower surface of the sheet feed roller

7

. The pushing device

20

will be described in more detail later.

The sheet feed roller

7

is disposed above the uncovered portion

4

b

of the sheet feed cassette

4

. The lower surface of the sheet feed roller

7

is opposed to the upper surface of the sheets P stacked in the sheet feed cassette

4

. The sheet feed roller

7

is supported by the main case

1

a

so as to rotate clockwise to supply the sheets P. A separation pad

8

, made of a synthetic resin, such as polyurethane, having an appropriate surface friction coefficient, is disposed underneath the sheet feed roller

7

to separate one sheet from a stack of sheets P in cooperation with the sheet feed roller

7

. Accordingly, as the sheet feed roller

7

rotates, the uppermost sheet is separated, with the aid of the separation pad

8

, from a stack of sheets P in the sheet feed cassette

4

and is conveyed. The sheet feed port

2

a

for supplying sheets P to the printing device

3

is formed by contact portions between the sheet feed roller

7

and the separation pad

8

.

A pair of driven rollers

9

,

9

are rotatably supported by the main case

1

a

so as to contact the sheet feed roller

7

. The sheet feed roller

7

and the driven rollers

9

,

9

pinch a sheet P therebetween and convey it. The sheet feed direction (indicated by arrow X

1

in

FIG. 1

) on the upstream side of the sheet feed roller

7

is opposite to that (indicated by arrow X

2

in

FIG. 1

) on the downstream side thereof.

In other words, in the printer

1

, the sheet feed path defined by the sheet feed roller

7

and the driven rollers

9

,

9

is bent into a U shape. A sheet P having passed along the sheet feed path and having undergone printing is discharged onto the upper surface of the cassette cover

5

of the sheet feed cassette

4

in which new sheets P are stored. With this structure, the printer

1

is made compact in size.

A linefeed roller

10

is disposed downstream of the sheet feed roller

7

to guide a sheet fed by the sheet feed roller

7

to a printhead

12

. The linefeed roller

10

is supported, similarly to the sheet feed roller

7

, by the main case

1

a

so as to rotate clockwise. A pressure roller

11

is disposed above the linefeed roller

10

to press the sheet P against the linefeed roller

10

. The pressure roller

11

operates in cooperation with the linefeed roller

10

to guide the sheet P to the printing device

3

.

The printing device

3

includes the printhead

12

that ejects ink onto the sheet P to accomplish printing. The printhead

12

is disposed downstream of the linefeed roller

10

and the pressure roller

11

. Nozzles

12

a

, through which ink is ejected onto the sheet P, are formed at the bottom of the printhead

12

. Below the nozzles

12

a

, a flat platen

13

is disposed to support the sheet P. Above the platen

13

, a carriage

14

is disposed to mount thereon the printhead

12

. The carriage

14

is translatable in the width direction of the sheet P. The carriage

14

has, besides the printhead

12

, an ink tank

15

for storing ink to be supplied to the printhead

12

.

Provided downstream of the printhead

12

and the platen

13

are a discharge roller

16

for discharging the sheet P discharged from the platen

13

to the outside of the main case

1

a

, and a pressure roller

17

for pressing the sheet P against the discharge roller

13

.

Downstream of the discharge roller

16

and the pressure roller

17

, the sheet discharge port

2

b

, thorough which the sheet P is discharged to the outside of the main case

1

a

, is formed higher than the sheet feed port

2

a

of the sheet feeder

2

.

Downstream of the sheet discharge port

2

b

, the cassette cover

5

is disposed to cover the covered portion

4

a

of the sheet feed cassette

4

. The cassette cover

5

serves as a holding member (a so-called output tray) that holds discharged printed sheets P and also as a holding member (a so-called manual feed tray) that holds new manually fed sheets P. The cassette cover

5

extends from a lower portion of the sheet discharge port

2

b

toward the sheet discharge direction (indicated by arrow X

2

in

FIG. 1

) to cover the sheet feed cassette

4

. Printed sheets P discharged from the sheet discharge port

2

b

are stacked on the upper surface of the cassette cover

5

.

FIG. 2

is an external perspective view of the sheet feed cassette

4

and the cassette cover

5

. The pressure plate

6

disposed within the sheet feed cassette

4

is omitted from FIG.

2

. Arrows shown in

FIG. 2

, as in the

FIG. 1

, indicate particular directions. Arrow A indicates the direction in which the sheet feed cassette

4

is inserted. Arrow X

1

indicates the sheet feed direction in which a sheet P is fed into the sheet feed port

2

a

. Arrow X

2

indicates the sheet discharge direction in which a sheet P is discharged onto the cassette cover

5

, and arrow X

3

indicates the direction in which a sheet P is manually fed from the cassette cover

5

.

The sheet feed cassette

4

includes the above-mentioned substantially rectangular, flat bottom plate

4

c

at the bottom thereof. Sidewalls

4

d

extends upward from four edges of the bottom plate

4

c

of the sheet feed cassette

4

. Thus, the sheet feed cassette

4

is a rectangular parallelepiped formed by the bottom plate

4

c

and the sidewalls

4

d

, with its top surface open, so as to accommodate a stack of sheets P.

In addition, a substantially rectangular cutaway

4

e

is formed in a sidewall

4

d

on one longitudinal end of the sheet feed cassette

4

, that is, in an upright sidewall

4

d

on the inserting direction side (indicated by arrow A). The sheet feed cassette

4

communicates with the outside thorough the cutaway

4

e

. The cutaway

4

e

for guiding the push plate

24

of the pushing device

20

is formed such that the push plate

24

can be inserted thereinto. Thus, the leading edge of the push plate

24

is allowed to make contact with the lower surface of the pressure plate

6

in the sheet feed cassette

4

.

On one side (right side in

FIG. 2

) of the sidewall

4

d

with the cutaway

4

e

, a substantially flat push-up plate

4

f

is provided so as to extend toward the sheet feed cassette inserting direction (indicated by arrow A in FIG.

2

). When the sheet feed cassette

4

is inserted into the cassette inserting section

1

b

, the push-up plate

4

f

pushes up an urging arm

22

(

FIGS. 3 and 4

) of the pushing device

20

. The urging arm

22

pushed up by the push-up plate

4

f

elastically deforms an elastic spring

25

of the pushing device

20

, thereby applying an urging force to the push plate

24

.

The cassette cover

5

includes the sheet edge-receiving portion

5

a

and the sheet-holding portion

5

b

, as described above. The partition

5

c

is vertically provided at the upper end of the sheet edge-receiving portion

5

a

, entirely along the width direction thererof. The manual sheet feed port

5

d

is wide open in the width direction of the sheet edge-receiving portion

5

d

. The longitudinal opening width of the manual sheet feed port

5

d

is slightly smaller than the width of the sheet edge-receiving portion

5

a.

Referring now to

FIG. 3

, the pushing device

20

will be described in detail.

FIG. 3

is a front view of the pushing device

20

. The right side in

FIG. 3

corresponds to the side far away from the reader in

FIG. 1

, and the left side corresponds to the side toward the reader. The gear teeth of a driving gear

27

, a first sub-gear

28

, a second sub-gear

30

, a transfer gear

31

a

of an attenuator

31

, and a gear teeth portion

32

a

of a ratchet gear

32

are omitted from FIG.

3

.

As shown in

FIG. 3

, the pushing device

20

includes a frame

20

a

bent by pressing a metal plate. On both lower sides (right and left sides in

FIG. 3

) of the frame

20

a

, substantially flat ribs

20

b

,

20

d

,

20

e

,

20

c

extend frontward (toward the reader in FIG.

3

). A main shaft

21

, which is substantially a round bar, is rotatably supported by the ribs

20

d

,

20

c

. Also, the main shaft

21

is prevented, by ribs

20

b

,

20

e

, from bending. The urging arm

22

pushed by the push-up plate

4

f

of the sheet feed cassette

4

is fixedly mounted to one end (on the right side in

FIG. 3

) of the main shaft

21

. On the left side of the urging arm

22

, an elastic spring

23

is disposed to urge the urging arm

22

downward.

Referring now to

FIG. 4

, the push-up plate

4

f

of the sheet feed cassette

4

and the elastic spring

23

of the urging arm

22

will be described in detail.

FIG. 4

is a right side sectional view of the pushing device

20

of

FIG. 3

, with the sheet feed cassette

4

partially removed. Arrow A in

FIG. 4

indicates the direction in which the sheet feed cassette

4

is inserted. As shown in

FIG. 4

, the push-up plate

4

f

of the sheet feed cassette

4

has a substantially horizontal engaging surface

4

f

1

at its upper end, and a guide surface

4

f

2

tilted down from one end (on the right side in

FIG. 4

) of the engaging surface

4

f

1

to the tip (on the right side in

FIG. 4

) of the push-up plate

4

f.

The urging arm

22

has a circular boss

22

a

at its one end (on the right side in FIG.

4

), and the main shaft

21

is fixedly mounted into the boss

22

a

. An inverted V-shaped arm portion

22

b

extends from the circumference of the boss

22

a

toward the side (left side in

FIG. 4

) away from the frame

20

a

. At the end opposite to the boss

22

a

, the arm portion

22

b

has a downwardly extending protrusion

22

c

, which is semicircular as viewed from the side. The protrusion

22

c

is formed so as to make contact with the push-up plate

4

f

of the sheet feed cassette

4

. The lower surface of the protrusion

22

c

makes contact with the guide surface

4

f

2

of the push-up plate

4

f.

The arm portion

22

b

has a substantially flat engaging protrusion

22

d

at its upper portion. The engaging protrusion

22

d

engages the extending hook

23

c

of the elastic spring

23

. The elastic spring

23

urges the arm portion

22

b

counterclockwise about the main shaft

21

, thereby urging the urging arm

22

downward. The elastic spring

23

is formed by winding a wire having restorable elasticity (an elastic material).

The elastic spring

23

includes a coil

23

a

, an extending portion

23

b

that extends from one end (left side in

FIG. 3

) of the coil

23

a

, and the extending hook

23

c

that extends from the other end (right side in

FIG. 3

) of the coil

23

a

. As shown in

FIG. 4

, the main shaft

21

is inserted through the coil

23

a

. The extending portion

23

b

engages the frame

20

a

, while the extending hook

23

a

engages the engaging protrusion

22

d

of the urging arm

22

.

When the sheet feed cassette

4

is removed from the cassette inserting section

1

b

, the elastic spring

23

urges the urging arm

22

counterclockwise about the main shaft

21

. As a result, the main shaft

21

is rotated counterclockwise, and, upon the counterclockwise rotation of the main shaft

21

, the push plate

24

is reliably lowered to its lower position (as shown in FIG.

1

).

On the other hand, when the sheet feed cassette

4

is inserted in the direction of arrow A, the guide surface

4

f

2

of the push-up plate

4

f

makes contact with the protrusion

22

c

, and the protrusion

22

c

slides upward over the guide surface

4

f

2

. When the protrusion

22

c

is pushed up, the urging arm

22

urged by the elastic spring

23

swings clockwise about the main shaft

21

. At this time, upon the clockwise swing of the urging arm

22

, the main shaft

21

is rotated clockwise.

As the main shaft

21

is rotated, the elastic spring

25

for urging the push plate

24

is elastically distorted, as described later, and a force for urging the push plate

24

is built up in the elastic spring

25

. In addition, the urging arm

22

is urged counterclockwise about the main shaft

21

by the elastic spring

23

as well as by an urging force built up in the elastic spring

25

.

After that, as the sheet feed cassette

4

continues to be inserted, the protrusion

22

c

reaches the engaging surface

4

f

1

, past the guide surface

4

f

2

, and is pressed against the engaging surface

4

f

1

by urging forces of the elastic springs

23

,

25

. As a result, the sheet feed cassette

4

is engaged in the cassette inserting section

1

b

so as not to be easily removed from the cassette inserting section

1

b

. So long as the sheet feed cassette

4

is kept inserted into the cassette inserting section

1

b

, the urging arm

22

is kept pushed up by the push-up plate

4

f

, thereby allowing the elastic spring

25

to build up an urging force.

Referring back to

FIG. 3

, a stopper

22

e

extends outward (leftward in

FIG. 3

) from the left side of the arm portion

22

b

of the urging arm

22

. The stopper

22

e

is in contact with the upper end of the rib

20

c

and restricts the downward swing of the downwardly-urged urging arm

22

. Thus, when the sheet feed cassette

4

is removed from the cassette inserting section

1

b

, the urging arm

22

is positioned to a predetermined position, as shown in FIG.

4

.

As shown in

FIG. 3

, the push plate

24

is disposed at a substantially central part in the axial direction (right/left direction in

FIG. 3

) of the main shaft

21

. The push plate

24

vertically moves the pressure plate

6

and includes a plate-like base

24

a

that extends downward from the main shaft

21

, a plate-like push portion

24

b

that extends forward (toward the reader in

FIG. 3

) horizontally from the base

24

a

, and substantially flat support plates

24

c

,

24

d

. The main shaft

21

is rotatably inserted through the support plates

24

c

,

24

d

. The main shaft

21

and the push plate

24

are linked by the support plates

24

c

,

24

d

through a bearing and a driving gear

27

.

In addition, the elastic spring

25

is attached to the main shaft

21

to apply an upward urging force to the push plate

24

. The elastic spring

25

is formed by winding a wire having restorable elasticity (an elastic material) and includes a cylindrically wound coil

25

a

, a pair of extending portions

25

b

,

25

c

that extend from both sides (right and left sides in

FIG. 3

) of the coil

25

a

, and a hook

25

d

provided at a substantially central part in the longitudinal direction (right/left direction in

FIG. 3

) of the coil

25

a.

The coil

25

a

of the elastic spring

25

is interposed between the support plates

24

c

,

24

d

of the push plate

24

, and the main shaft

21

is inserted through the coil

25

a

(FIG.

5

). The extending portions

25

b

,

25

c

are engaged in holes

24

a

1

,

24

a

2

provided in the base

24

a

. The hook

25

d

is hooked over a screw

26

screwed into the circumference of the main shaft

21

.

The driving gear

27

is disposed adjacent to and on the right side of the support plate

24

d

of the push plate

24

. The driving gear

27

is a gear wheel rotated in response to the vertical movement of the push plate

24

and has a plurality of gear teeth on its circumference. A substantially cylindrical boss

27

a

is provided so as to extend toward the support plate

24

d

from a lower portion of the driving gear

27

. The boss

27

a

is engaged in a hole

24

d

1

drilled through the support plate

24

d

(FIG.

5

). Thus, the driving gear

27

can be rotated as the push plate

24

vertically moves.

A first sub-gear

28

is disposed above the driving gear

27

. The first sub-gear

28

is rotated by the rotation of the driving gear

27

and has, on its circumference, gear teeth that mesh with the gear teeth of the driving gear

27

. The first sub-gear

28

is fixedly attached to one end (on the right side in

FIG. 3

) of a driven shaft

29

disposed in substantially parallel with the main shaft

21

. The driven shaft

29

is rotatable by the rotation of the first sub-gear

28

. Also, the driven shaft

29

is rotatably supported at its both ends (right and left sides in

FIG. 3

) by the flat ribs

20

d

,

20

e

that extend frontward (toward the reader in

FIG. 3

) from the frame

20

a.

Referring now to

FIG. 5

, the push plate

24

, the elastic spring

25

, the screw

26

, the driving gear

27

, the first sub-gear

28

, and the driven shaft

29

will be described in detail.

FIG. 5

is a side sectional view taken along line V—V of

FIG. 3

, with the respective circumferential gear teeth of the driving gear

27

and the first sub-gear

28

omitted. The pitch circles of the driving gear

27

and the first sub-gear

28

are shown by long and short dashed lines, while their addendum circles and bottom circles are shown by solid lines.

As shown in

FIG. 5

, the base

24

a

of the push plate

24

is bent into Z shape as viewed from the side. At the lower portion of the base

24

a

, the hole

24

a

2

is formed through the plate of the base

24

a

. The extending portion

25

c

of the elastic spring

25

is inserted into the hole

24

a

2

and engaged with the lower edge of the hole

24

a

2

. By the engagement of the extending portion

25

c

(and the extending portion

25

b

) of the elastic spring

25

with the base

24

a

of the push plate

24

, the base

24

a

is urged counterclockwise in

FIG. 5

about the main shaft

21

, thereby moving upward the push plate

24

.

The substantially flat push portion

24

b

is formed continuously from the lower end of the base

24

a

. The push portion

24

b

extends from the base

24

a

substantially horizontally toward the direction (rightward in

FIG. 5

) away from the frame

20

a

. The inverted V-shaped contact

24

e

is formed at the leading edge of the push portion

24

b

. The contact

24

e

projects upward and makes contact, at its top, with the lower surface of the pressure plate

6

(FIG.

1

).

The elastic spring

25

is provided such that the coil

25

a

is wounded around the main shaft

21

and the hook

25

d

is hooked over the screw

26

screwed into the main shaft

21

. Thus, when the main shaft

21

is rotated (counterclockwise in FIG.

5

), the screw

26

swings counterclockwise and the hook

25

d

is moved up counterclockwise about the main shaft

21

. As a result, the coil

25

a

of the elastic spring

25

is elastically distorted. An elastic restoring force built up in the elastic spring

25

c

due to such distortion is generated from the extending portions

25

b

,

25

c

as upward urging forces.

The hole

24

d

1

is formed in the support plate

24

d

of the push plate

24

, and the boss

27

a

, projecting from the driving gear

27

, is engaged in the hole

24

d

1

. The drive gear

27

has gear teeth on its circumference, and the gear teeth of the first sub-gear

28

mesh therewith. The first sub-gear

28

has gear teeth on its circumference, and the driven shaft

29

is fixedly attached to the center of the first sub-gear

28

.

Referring back to

FIG. 3

, the second sub-gear

30

is fixedly attached to the other end (on the left side in

FIG. 3

) of the driven shaft

29

. The second sub-gear

30

is a gear wheel rotated by the rotation of the driven shaft

29

and has gear teeth on its circumference. The attenuator

31

is disposed above the second sub-gear

30

. The attenuator

31

is a rotary damper for attenuating the rotation speed of the second sub-gear

30

and includes the transfer gear

31

a

for transferring a rotating force of the second sub-gear

30

and a case

31

b

filled with a viscous material.

The transfer gear

31

a

has, on its circumference, gear teeth that mesh with the gear teeth of the second sub-gear

30

to transfer the rotation of the second sub-gear

30

. The transfer gear

31

a

is linked to an impeller wheel (not shown) housed in the case

31

b

, and as the transfer gear

31

a

rotates, the impeller wheel rotates. Because the impeller wheel rotates within the case

31

b

filled with the viscous material, such as grease, the rotation speed of the second sub-gear

30

is attenuated.

By attenuating the rotation speed of the second sub-gear

30

, the rotation speed of the driving gear

27

is attenuated through the driven shaft

29

and the first sub-gear

28

. Thus, the speed at which the push plate

24

vertically moves as the drive gear

27

rotates is attenuated. Particularly, the moving up speed of the push plate

24

when urged by the elastic spring

25

is attenuated.

The ratchet gear

32

is disposed below the second sub-gear

30

and includes the gear teeth portion

32

a

for receiving the rotation of the second sub-gear

30

and a ratchet pawl portion

32

b

. The gear teeth portion

32

a

is substantially cylindrical and has, on its circumference, gear teeth that mesh with the gear teeth of the second sub-gear

30

. On the left side of the gear teeth portion

32

a

, the ratchet pawl portion

32

b

having a larger outside diameter than the gear teeth portion

32

a

is formed integrally with the gear teeth portion

32

a.

A lock shaft

33

, which is substantially a round bar, is disposed below the ratchet gear

32

. The lock shaft

33

is rotatably supported at its both ends (on the right and left sides in

FIG. 3

) by substantially flat ribs

20

f

,

20

g

extending from the frame

20

a

. The lock shaft

33

supports a lock

34

extending toward the ratchet pawl portion

32

b

of the ratchet gear

32

. The lock

34

restricts the forward rotation (counterclockwise rotation indicated by arrow B in

FIG. 6

) of the ratchet gear

32

and permits the reverse rotation (clockwise rotation in

FIG. 6

) thereof. The lock shaft

33

is inserted through the lower end of the lock

34

, and an elastic spring

35

is disposed on the left side of the lock

34

to urge the lock

34

upward.

Referring now to

FIG. 6

, the second sub-gear

30

, the ratchet gear

32

, the lock shaft

33

, the lock

34

, and an elastic spring

35

will be described in detail.

FIG. 6

is a side sectional view taken along line VI—VI of

FIG. 3

, with the circumferential gear teeth of the second sub-gear

30

and the circumferential gear teeth of the gear teeth portion

32

a

of the ratchet gear

32

omitted. The pitch circles of the second sub-gear

30

and the gear teeth portion

32

a

are shown by alternate long and short dashed lines, while their addendum circles and bottom circles are shown by broken lines. Arrow B indicates the (forward) direction in which the ratchet gear

32

rotates as the push plate

24

moves up.

As shown in

FIG. 6

, the driven shaft

29

is disposed at a substantially central part in the vertical direction of the frame

20

a

. The second sub-gear

30

is fixedly attached to the driven shaft

29

. The second sub-gear

30

has gear teeth on its entire circumference. The attenuator disposed above the second sub-gear

30

is screw-fastened to the frame

20

a

. On the other hand, the ratchet gear

32

is disposed below the second sub-gear

30

.

The ratchet gear

32

includes the gear teeth portion

32

a

(on the side away from you in

FIG. 6

) and the ratchet pawl portion

32

b

(on the side toward you in FIG.

6

). The main shaft

21

is rotatably inserted through the central parts of the gear teeth portion

32

a

and the ratchet pawl portion

32

b

. The gear teeth portion

32

a

has, on its entire circumference, gear teeth that mesh with the gear teeth of the second sub-gear

30

. Thus, the second sub-gear

30

can transfer the rotation of the ratchet gear

32

, and vice versa.

The ratchet pawl portion

32

b

of the ratchet gear

32

is integrally formed with the gear teeth portion

32

a

and has substantially acute ratchet pawls

32

c

at predetermined intervals on its circumference. A lock pawl

34

a

of the lock

34

is engageable with a recess between the consecutive ratchet pawls

32

c

. At a lower portion of the ratchet pawl portion

32

b

, the lock pawl

34

a

is engaged with a recess between the consecutive ratchet pawls

32

c

. At an upper portion, near the frame

20

a

(on the left side in FIG.

6

), of the ratchet pawl portion

32

b

, a ratchet pawl-absent portion

32

d

, which will be described later, is formed.

The lock

34

is disposed below the ratchet gear

32

. The lock shaft

33

is inserted through one end (on the left side in

FIG. 6

) of the lock

34

. The lock

34

extends from the lock shaft inserting section upward away from the frame

20

a

(toward the upper right in FIG.

6

). The acute lock pawl

34

a

projects from the upper surface at the extending end of the lock

34

toward the ratchet pawl portion

32

b

so as to engage with the ratchet pawl

32

c.

When the lock pawl

34

a

is engaged with a ratchet pawl

32

c

, the lock pawl

34

a

restricts the counterclockwise rotation (forward rotation indicated by arrow B in

FIG. 6

) of the ratchet gear

32

, and permits the clockwise rotation (reverse rotation opposite to the direction of arrow B in

FIG. 6

) thereof. When the lock pawl

34

a

is released from engagement with the ratchet pawl

32

c

, the ratchet gear

32

is rotatable in either direction, counterclockwise or clockwise in FIG.

6

.

The rotation of the ratchet gear

32

in the direction of arrow B (counterclockwise rotation in

FIG. 6

) is referred to as “forward rotation”, and the rotation of the ratchet gear

32

in the direction opposite to arrow B (clockwise rotation in

FIG. 6

) as “reverse rotation” hereinafter.

The lock

34

has a pushed-down portion

34

b

disposed at the extending end (on the upper right side in

FIG. 6

) beyond the lock pawl

34

a

. The pushed-down portion

34

b

is pushed down by a release cam

42

a

of a coupled cam

42

at predetermined times, as described later. When the pushed-down portion

34

b

is pushed down, the lock

34

swings clockwise in

FIG. 6

about the lock shaft

33

, thereby releasing the lock pawl

34

a

from engagement with the ratchet pawl

32

c.

A coil

35

a

of an elastic spring

35

is wounded around the lock shaft

33

inserted through the lock

34

. The elastic spring

35

, formed by winding a wire having restorable elasticity, urges the lock

34

toward the ratchet pawl portion

32

b

(upward in FIG.

6

). The elastic spring

35

includes the cylindrically wound coil

35

a

, an extending portion

35

b

that extends from one end (on the left side in

FIG. 6

) of the coil

35

a

, and an extending hook

35

c

that extends from the other end (on the right side in

FIG. 6

) of the coil

35

a.

As shown in

FIG. 6

, the lock shaft

33

is inserted through the coil

35

a

. The extending portion

35

b

is pressed against a base plate

20

a

1

that extends substantially horizontally from the lower end of the frame

20

a

, while the extending hook

35

c

is engaged with the lower surface of the lock

34

. Thus, the lock

34

is urged counterclockwise in

FIG. 6

about the lock shaft

33

, thereby pushing the lock pawl

34

a

against the ratchet pawl

32

b

to bring them into secure engagement with each other.

Referring back to

FIG. 3

, a lowering mechanism

36

is disposed on the opposite side (on the left side in

FIG. 3

) of the ratchet gear

32

from the push plate

24

. The lowering mechanism

36

lowers the push plate

24

by a predetermined distance from a position where a stack of sheets P on the pressure plate

6

is in contact with the sheet feed roller

7

(

FIG. 9

) to a position where a stack of sheets P on the pressure plate

7

is away from the sheet feed roller

7

(FIG.

10

).

The position of the push plate

24

when a stack of sheets P is in contact with the sheet feed roller

7

(as shown in

FIG. 9

) is referred to as a “plate upper position” hereinafter. On the other hand, the position of the push plate

24

when the pressure plate

6

is placed substantially horizontally, adjacent to the bottom plate

4

c

of the sheet feed cassette

4

, while the stack of sheets P is greatly away from the sheet feed roller

7

(as shown in

FIG. 1

) is referred to as a “plate lower position”. Further, the position of the push plate

24

when a stack of sheets P is away from the sheet feed roller

7

by a predetermined distance (as shown in

FIG. 10

) is referred to as a “plate standby position”.

The lowering mechanism

36

includes the above-described ratchet pawl portion

32

b

of the ratchet gear

32

, an engaging member

37

that engages the ratchet pawl portion

32

b

to rotate in reverse the ratchet gear

32

, an actuating member

38

that transfers a force for rotating in reverse the ratchet gear

32

to the engaging member

37

, and two elastic springs

39

,

40

for urging the engaging member

37

and the actuating member

38

, respectively.

The engaging member

37

is interposed between the second sub-gear

30

and the actuating member

38

and includes a movable arm

37

a

, disposed above the ratchet pawl portion

32

b

of the ratchet gear

32

, and an engaging pawl

37

b

engageable with the ratchet pawl

32

c

. A connecting shaft

37

c

extends from one side (left side in

FIG. 3

) of the movable arm

37

a

to the actuating member

38

and is connected to the actuating member

38

such that the actuating member

38

swings. Above the connecting shaft

37

c

, a spring-holding arm

37

d

extends in the same direction (leftward in

FIG. 3

) in which the connecting shaft

37

c

extends. The upper end of the elastic spring

39

is hooked over the spring-holding arm

37

d.

The actuating member

38

is disposed adjacent to (on the left side in

FIG. 3

) the ratchet pawl portion

32

b

and includes a pushed-down portion

38

a

to be pushed down by a push-down cam

42

b

of the coupled cam

42

, which will be described later, and a spring-holding arm

38

b

over which the lower end of the elastic spring

40

is hooked.

Referring now to

FIGS. 7 and 8

, the lowering mechanism

36

will be described in detail.

FIG. 7

is a side sectional view of the lowering mechanism

36

, with the elastic springs

39

,

40

omitted.

As shown in

FIG. 7

, the engaging member

37

rotates in reverse (in the clockwise direction in

FIG. 7

, in the direction opposite to arrow B in

FIG. 7

) the ratchet gear

32

to lower the push plate

24

and includes the movable arm

37

a

having an inverted V-shape as viewed from the side. The movable arm

37

a

is slightly tilted down from one end near the frame

20

a

to the other end away from the frame

20

a

. The acute engaging pawl

37

b

projects downward from one end (on the left side in

FIG. 7

) of the movable arm

37

a

. The engaging pawl

37

b

is engageable with the ratchet pawl

32

c

of the ratchet pawl portion

32

b

disposed below the engaging member

37

.

The connecting shaft

37

c

is provided on the other end (on the right side in

FIG. 7

) of the movable arm

37

a

and is connected to a connecting hole

38

c

formed at an upper portion of the actuating member

38

such that the actuating member swings. The spring-holding arm

37

d

is provided at an upper portion on the engaging pawl side (left side in

FIG. 7

) of the movable arm

37

a

. The upper end of the elastic spring

39

is hooked over the spring-holding arm

37

d

. A stopper

37

e

, which is substantially rectangular as viewed from the side, projects from the end formed with the engaging pawl

37

b

(on the left side in

FIG. 7

) toward the frame

20

a

(leftward in FIG.

7

). The stopper

37

e

makes contact with a stopper plate

20

a

2

provided to the frame

20

a

, thereby restricting the movement of the engaging member

37

toward the frame

20

a

(leftward in FIG.

7

).

The ratchet pawl-absent portion

32

d

, which lacks, for example, three ratchet pawls

32

c

, is provided so as to oppose the engaging pawl

37

b

of the engaging member

37

. Thus, when the push plate

24

is at the plate lower position, the engaging pawl

37

b

is not allowed to engage the ratchet pawl-absent portion

32

d

. Thus, the push plate

24

is prevented from being lowered below the plate lower position. As a result, the pushing device

20

is prevented from breaking down due to excessive lowering of the push plate

24

.

The main shaft

21

is rotatably inserted in the actuating member

38

. The pushed-down portion

38

a

extends from the main shaft-inserting portion downward away from the frame

20

a

(toward the lower right in FIG.

7

). The pushed-down portion

38

a

is pushed down by the push-down cam

42

b

of the coupled cam

42

at predetermined times, as described later. Subsequently, the actuating member

38

swings clockwise about the main shaft

21

.

The spring-holding arm

38

b

is disposed above the main shaft-inserting portion and slightly closer to the pushed-down portion

38

a

(on the right side in FIG.

7

). A substantially ring-shaped hook

40

a

at the lower end of the elastic spring

40

is hooked over the spring-holding arm

38

b

(FIG.

8

). Also, a spring-holding hook

38

d

is provided above the main shaft-inserting portion of the actuating member

38

. A substantially ring-shaped hook

39

a

at the lower end of the elastic spring

39

is hooked over the spring-holding hook

38

d

(FIG.

8

).

FIG. 8

is a side sectional view taken along line VII—VII of FIG.

3

. The elastic springs

39

,

40

are shown by alternate long and two short dashed lines.

The elastic spring

39

is formed by winding a wire having restorable elasticity to urge the end formed with the engaging pawl

37

b

toward the actuating member

38

. The substantially ring-shaped hook

39

a

formed at the lower end of the elastic spring

39

is hooked over the spring-holding hook

38

d

of the actuating member

38

. Also, the substantially ring-shaped hook

39

b

formed at the upper end of the elastic spring

39

is hooked over the spring-holding arm

37

d

of the engaging member

37

. Thus, the end formed with the engaging pawl

37

b

is urged toward the actuating member

38

.

The elastic spring

40

is formed by winding a wire having restorable elasticity to urge the actuating member

38

upward (counterclockwise in

FIG. 8

) about the main shaft

21

. The substantially ring-shaped hook

40

a

formed at the lower end of the elastic spring

40

is hooked over the spring-holding arm

38

b

of the actuating member

38

. Also, the substantially ring-shaped hook

40

b

formed at the upper end of the elastic spring

40

is hooked over a spring-holding hook

20

a

3

formed at an upper portion of the frame

20

a

above the actuating member

38

. Thus, the actuating member

38

is urged by the elastic spring

40

upward (counterclockwise in

FIG. 8

) about the main shaft

21

.

Referring back to

FIG. 3

, a drive shaft

41

, which is substantially a round bar, is interposed between the main shaft

21

and the lock shaft

33

. The drive shaft

41

is rotatably supported at its both ends (right and left sides in

FIG. 3

) by the substantially flat ribs

20

b

,

20

c

extending from the frame

20

a

. The drive shaft

41

is connected, at its one end (on the left side in FIG.

3

), to a rotary shaft of the sheet feed roller

7

through a gear mechanism (not shown) so as to rotate unidirectionally (counterclockwise in

FIG. 7

) as the sheet feed roller

7

rotates.

The coupled cam

42

is fixedly mounted at an axially central portion of the drive shaft

41

so as to be opposed to the lock

34

and the actuating member

38

. The coupled cam

42

includes the release cam

42

a

(on the right side in

FIG. 3

) opposed to the lock

34

and the push-down cam

42

b

(on the left side in

FIG. 3

) opposed to the pushed-down portion

38

a

. The release cam

42

a

and the push-down cam

42

b

are integrally formed.

Referring now to

FIG. 7

, the coupled cam

42

will be described in detail. As shown in

FIG. 7

, the drive shaft

41

is fixedly attached into the coupled cam

42

so as to allow the coupled cam

42

to rotate counterclockwise in FIG.

7

.

The substantially semicircular release cam

42

a

is formed about half way around the coupled cam

42

. The release cam

42

a

pushes down the pushed-down portion

34

b

of the lock

34

at predetermined times to release the lock pawl

34

a

of the lock

34

from engagement with the ratchet pawl

32

c

of the ratchet pawl portion

32

b

. While the drive shaft

41

makes a half-turn, the release cam

42

a

keeps pushing down the pushed-down portion

34

b

of the lock

34

, thereby releasing the lock pawl

34

a

from engagement with the ratchet pawl

32

c.

On the other hand, the push-down cam

42

b

extends outward from the side opposite to the release cam

42

a

. The push-down cam

42

b

pushes down the pushed-down portion

38

a

of the actuating member

38

at predetermined times to swing the actuating member

38

clockwise in

FIG. 7

about the main shaft

21

. While the drive shaft

41

rotates by a predetermined angle, the push-down cam

42

keeps pushing down the actuating member

38

, thereby swinging the actuating member

38

clockwise in FIG.

7

.

The sheet feed operation in the printer

1

having the sheet feeder

2

as structured above will now be described.

FIG. 9

is a side sectional view showing the internal structure of the printer

1

, with the push plate

24

at the plate upper position.

FIG. 10

is a side sectional view showing the internal structure of the printer

1

, with the push plate

24

at the standby position.

As shown in

FIG. 1

, a stack of sheets P to be printed are placed on the top surface of the pressure plate

6

in the sheet feed cassette

4

. Then, the covered portion

4

a

of the open surface of the sheet feed cassette

4

is covered by the cassette cover

5

. After that, upon the insertion of the sheet feed cassette

4

into the cassette inserting section

1

b

, an edge (on the left side in

FIG. 1

) of a stack of sheets P in the sheet feed cassette is placed below the sheet feed roller

7

. Thereby, the sheet setting is completed.

On the other hand, as shown in

FIG. 4

, upon the insertion of the sheet feed cassette

4

, the push-up plate

4

f

of the sheet feed cassette

4

approaches to the urging arm

22

, and the guide surface

4

f

2

of the push-up plate

4

f

makes contact with the protrusion

22

c

of the urging arm

22

.

After that, when the sheet feed cassette

4

continues to be inserted, the push-up plate

4

f

moves underneath the urging arm

22

in the direction of arrow A, thereby causing the protrusion

22

c

to slide up along the guide surface

4

f

2

.

As the protrusion

22

c

slides up, the urging arm

22

swings upward (clockwise in

FIG. 4

) about the main shaft

21

against the urging force of the elastic spring

23

. When the sheet feed cassette

4

still continues to be inserted, the protrusion

22

c

of the urging arm

22

reaches the engaging surface

4

f

1

of the push-up plate

4

f

, and the urging arm

22

presses the push-up plate

4

f.

This pressing force maintains pressured contact of the urging arm

22

to the sheet feed cassette

4

and securely prevents the sheet feet cassette

4

from being removed from the cassette inserting section

1

b.

As the urging arm

22

swings upward (clockwise in FIG.

4

), the main shaft

21

is rotated counterclockwise in FIG.

5

. This makes the screw

26

screwed into lie main shaft

21

swing counterclockwise in FIG.

5

. By the swing of the screw

26

, the hook

25

d

of the elastic spring

25

is moved up. As a result, the coil

25

a

of the elastic spring

25

is elastically distorted. An elastic restoring force is built up due to such distortion in the elastic spring

25

as a force for urging the push plate

24

.

As described above, when the sheet feed cassette

4

is inserted and an urging force is built up in the elastic spring

25

, the ratchet pawl

32

c

of the ratchet gear

32

is engaged with the lock pawl

34

a

of the lock

34

, as shown in

FIGS. 1

,

6

, and

7

, Thus, the lock

34

restricts the rotation of the ratchet gear

32

in the forward direction (counterclockwise direction indicated by arrow B in FIGS.

6

and

7

). This restriction further restricts the rotation of the second sub-gear

30

in mesh with the gear teeth portion

32

a

of the ratchet gear

32

. As a result, the rotation of the driven shaft

29

, the first sub-gear

28

, and the driving gear

27

are restricted. By the rotation restriction on the driving gear

27

, the push plate

24

engaged with the driving gear

27

through the boss

27

a

is halted at the plate lower position, as shown in

FIG. 5

, with the push portion

24

b

substantially horizontal.

If a sheet feed command is transmitted from a controller (not shown) when the sheet feed roller

7

rotates clockwise in

FIG. 1

after the insertion of the sheet feed cassette

4

, a lock lever (not shown) is released by a solenoid (not shown). As a result, the drive shaft

41

shown in

FIGS. 6

to

8

is rotated counterclockwise through a gear mechanism (not shown), and then stopped by the lock lever.

The stopped drive shaft

41

is rotated again when another sheet feed command is transmitted again from the controller. In other words, the drive shaft

41

is rotationally driven intermittently upon receipt of a sheet feed command.

By the rotation of the drive shaft

41

, the coupled cam

42

is rotated to bring the release cam

42

a

of the coupled cam

42

into contact with the pushed-down portion

34

b

of the lock

34

. When the sheet feed roller

7

continues to rotate and the drive shaft

41

is further rotated, the release cam

42

a

pushes the pushed-down portion

34

b

of the lock

34

. This makes the lock

34

swing down, against the urging force of the elastic spring

35

, clockwise in

FIGS. 6

to

8

, about the lock shaft

33

.

When the lock

34

swings down, the lock pawl

34

a

is released from the ratchet pawl

32

c

, and the lock

34

is released from the engagement with the ratchet gear

32

. This allows the ratchet gear

32

to rotate about the main shaft

21

. As a result, the second sub-gear

30

in mesh with the gear teeth portion

32

a

of the ratchet gear

32

, the driven shaft

29

, the first sub-gear

28

, and the driving gear

27

are allowed to rotate.

Then, the extending portions

25

b

,

25

c

of the elastic spring

25

starts moving up by an elastic restoring force built up in the elastic spring

25

by the insertion of the sheet feed cassette

4

. More specifically, the extending portion

25

c

of the elastic spring

25

starts swinging counterclockwise in

FIG. 5

about the main shaft

21

. Simultaneously, the push plate

24

swings counterclockwise about the main shaft

21

, thereby moving up the push portion

24

b

and the contact portion

24

e

of the push plate

24

.

When the push plate

24

is moved up, the contact portion

24

makes contact with the lower surface of the pressure plate

6

. Then, the push plate

24

pushes up the pressure plate

6

and pivots the pressure plate

6

clockwise in

FIG. 1

about the pivot shaft

6

a

. The push plate

24

urged by the elastic spring

25

moves the pressure plate

6

up further, thereby pressing a stack of sheets P placed on the pressure plate

6

against the lower surface of the sheet feed roller

7

.

After that, when the sheet feed roller

7

further rotates clockwise in

FIG. 9

, the sheet feed roller

7

separates the uppermost sheet of the stack in cooperation with the separation pad

8

. When the sheet feed roller

7

further rotates after separating the uppermost sheet, the pressure plate

6

pushed up by the push plate

24

is lowered by a predetermined distance.

To be more specific, as the sheet feed roller

7

further rotates, the drive shaft

41

is further rotated counterclockwise in FIG.

6

. This makes the coupled cam

42

further rotate, and the release cam

42

a

of the coupled cam

42

comes off the pushed-down portion

34

b

of the lock

34

. The pushed-down portion

34

b

is released by the release cam

42

a

. Thus, the lock

34

is urged counterclockwise about the lock shaft

33

by an elastic restoring force of the elastic spring

35

, thereby bringing the lock pawl

34

a

into engagement with the ratchet pawl

32

c

of the ratchet gear

32

. This engagement restricts the forward rotation (indicated by arrow B in

FIG. 6

) of the ratchet gear

32

.

Then, the rotation of the second sub-gear

30

in mesh with the gear teeth portion

32

a

of the ratchet gear

32

is restricted and, as a result, the rotations of the driven shaft

29

, the first sub-gear

28

, and the driving gear

27

are restricted. By the rotation restriction on the driving gear

27

, the push plate

24

engaged with the drive gear

27

through the boss

27

a

is halted at the plate upper position, as shown in FIG.

9

. After that, when the sheet feed roller

7

further rotates, the drive shaft

41

is further rotated counterclockwise in FIG.

7

.

Then, the push-down cam

42

b

of the coupled cam

42

is brought into contact with the pushed-down portion

38

a

of the actuating member

38

. When the drive shaft

41

is further rotated by the continuous rotation of the sheet feed roller

7

, the push-down cam

42

b

pushes down the pushed-down portion

38

a

of the actuating member

38

. This makes the actuating member

38

swing down, against the urging force of the elastic spring

40

, clockwise in

FIG. 7

about the main shaft

21

. When the actuating member

38

swings down, the elastic spring

40

is elongated longitudinally and a restoring elastic force is built up therein.

On the other hand, when the actuating member

38

swings down, the connecting shaft side end of the engaging member

37

is moved down, through the connecting shaft

37

c

connected into the connecting hole

38

c

of the actuating member

38

, in the swing direction of the actuating member

38

. Then, the engaging pawl side end of the engaging member

37

is lowered toward the actuating member

38

by an elastic restoring force of the elastic spring

39

. Thus, the engaging pawl

37

b

is brought into engagement with the ratchet pawl

32

c

of the upper ratchet pawl portion

32

b

of the ratchet gear

32

.

After that, when the sheet feed roller

7

further rotates, the drive shaft

41

is further rotated counterclockwise in FIG.

7

. This makes the coupled cam

42

further rotate so that the push-down cam

42

b

further pushes the pushed-down portion

38

a

of the actuating member

38

. Then, the actuating member

38

further swings down clockwise in

FIG. 7

about the main shaft

21

. Thereby, the engaging member

37

is moved in the reverse rotation direction (in the direction opposite to arrow B in

FIG. 7

) of the ratchet gear

32

with the engaging pawl

37

b

engaged with the ratchet pawl

32

c

. As a result, the ratchet gear

32

is rotated in reverse by a predetermined angle.

Subsequently, the gear teeth portion

32

a

of the ratchet gear

32

, the ratchet gear

32

, the second sub-gear

30

in mesh with the gear teeth portion

32

a

, the driven shaft

29

, the first sub-gear

28

, and the driving gear

27

are rotated. By the rotation of the driving gear

27

, the push plate

24

is lowered to the plate standby position, as shown in FIG.

10

. This makes the extending portions

25

b

,

25

c

swing down and an corresponding urging force is built up again in the elastic spring

25

.

After that, the next sheet feed command is transmitted from the controller, intermittent rotation of the drive shaft

41

is started. This makes the coupled cam

42

further rotate, and the push-down cam

42

b

of the coupled cam

42

comes off the pushed-down portion

38

a

of the actuating member

38

. Thus, the pushed-down portion

38

a

is released by the push-down cam

42

b

. Then, the actuating member

38

is urged by an elastic restoring force of the elastic spring

40

to swing up counterclockwise in

FIG. 8

about the main shaft

21

. As the actuating member

38

swings up, the engaging member

37

moves up, thereby disengaging the engaging pawl

37

b

from the ratchet pawl

32

c

of the ratchet gear

32

and returning them into a state shown in

FIGS. 7 and 8

. Even when the engaging pawl

37

b

is disengaged from the ratchet pawl

32

c

, the lock pawl

34

a

remains engaged with the ratchet pawl

32

c

. Thus, the push plate

24

is halted at the plate standby position as shown in FIG.

10

.

When the push plate

24

is lowered by a predetermined distance from the plate upper position (as shown in

FIG. 9

) to the plate standby position (as shown in FIG.

10

), the pressure plate

6

having been moved up by the pushed plate

24

is also lowered by a predetermined distance. As a result, a stack of sheets P placed on the pressure plate

6

falls away from the sheet feed roller

7

by a predetermined distance. In this state, a separated sheet P is fed downstream, by the sheet feed roller

7

and the driven rollers

9

,

9

, along the sheet feed path (in the direction indicated by arrow X

1

in FIG.

1

). The sheet feed direction on the upstream side is reversed from the downstream side. Specifically, the sheet P is fed upward from the sheet feed port

2

a

along the rotation direction of the sheet feed roller

7

. When the sheet P reaches the upper surface of the sheet feed roller

7

, the sheet feed direction is reversed from the direction (indicated by arrow X

1

in

FIG. 1

) in which the sheet is fed from the sheet feed cassette

4

to the direction indicated by arrow X

2

in FIG.

1

.

The sheet P fed by the sheet feed roller

7

is conveyed over the platen

13

. Then, the sheet P passes underneath the printhead

12

mounted on the carriage

14

of the printer

3

while being supported by the platen

13

. While the sheet P passes underneath the printhead

12

, printing is accomplished by ink ejection from the ink tank

15

through the nozzles

12

a

of the printhead

12

onto the sheet P.

The printed sheet P is conveyed by the discharge roller

16

and the pressure roller

17

, through the sheet discharge port

2

b

, onto the upper surface of the cassette cover

5

. The trailing edge (on the left side in

FIG. 1

) of the sheet P discharged onto the cassette cover

5

is held by the sheet edge-receiving portion

5

a

, while the leading edge (on the right side in

FIG. 1

) thereof is held by the sheet-holding portion

5

b.

After that, the next sheet feed command is transmitted from the controller, intermittent rotation of the drive shaft

41

is started again. By the rotation of the drive shaft

41

, the lock release cam

42

a

of the coupled cam

42

pushes the pushed-down portion

34

b

of the lock

34

, thereby disengaging the lock pawl

34

a

of the lock

34

from the ratchet pawl

32

c

of the ratchet gear

32

. Thus, the push plate

24

is moved up to the plate upper position by an elastic restoring force of the elastic spring

25

. As the push plate

24

is moved up, a stack of sheets P placed on the pressure plate

6

is brought into contact with the lower surface of the sheet feed roller

7

again, as shown in FIG.

9

. The next sheet P of the stack is supplied to the printer

3

so as to be printed thereon.

As described above, in the printer

1

having the sheet feeder

2

in accordance with the embodiment, the push plate

24

is lowered by a predetermined distance by the lowering mechanism

36

actuated by the coupled cam

42

when a separated sheet P is conveyed by the sheet feed roller

7

. The push plate

24

is halted at the plate standby position, which is lower than the plate upper position and higher than the plate lower position, by the engagement between the ratchet pawl

32

c

and the lock pawl

34

a

. Accordingly, a sheet P separated by the sheet feed roller

7

and the separation pad

8

is not pressed against the sheet feed roller

7

, and thus the rotation load of the sheet feed roller

7

can be reduced.

The push plate

24

is lowered by a predetermined distance and halted at the plate standby position, which is higher than the plate lower position, by the engagement between the ratchet pawl

32

c

and the lock pawl

34

a

. Accordingly, the push plate

24

does not need to be lowered to the plate lower position as opposed to a conventional sheet feeder. Thus, the vertical moving distance of the push plate

24

after the sheet separation is shortened. Because of the shortened moving distance of the push plate

24

, impact noise produced upon the contact between a stack of sheets P on the pressure plate

6

raised by the push plate

24

and the sheet feed roller

7

is reduced.

As the moving distance of the pressure plate

6

is shortened, the moving time of the pressure plate

6

is also reduced. Thus, no expensive high-torque drive motor is required to vertically move the pressure plate

6

at high speed, resulting in a reduction in the total production cost of the sheet feeder

2

.

Further, because the moving time of the pressure plate

6

is reduced as the moving distance of the pressure plate

6

is shortened, time required for a sheet P to be fed can be reduced and the sheet feed speed of the sheet feeder

2

can be increased.

Lowering of the push plate

24

by a predetermined distance to the plate stand by position is initiated by the coupled cam

42

. The coupled cam

42

, when rotated in response to the sheet feed roller

7

, pushes the actuating member

38

and swings the engaging portion

37

in the reverse rotation direction of the ratchet gear

32

. This makes the ratchet pawl portion

32

b

of the ratchet gear

32

rotate in reverse, thereby lowering the push plate

24

. The driving force of the sheet feed roller

7

is used as the driving force for lowering the push plate

24

. Thus, no extra drive unit such as a motor is required for lowering the push plate

24

, resulting in a reduction in the total production cost of the sheet feeder

2

.

When the ratchet gear

32

is rotated in reverse by a predetermined angle by the engaging member

37

, the actuating member

38

is released by the coupled cam

42

. This disengages the engaging member

37

from the ratchet gear

32

. The disengagement restricts the reverse rotation of the ratchet gear

32

by the engaging portion

37

and prevents the push plate

24

from being lowered excessively more than a predetermined distance. Thus, the push plate

24

is lowered by a predetermined distance without the use of a position sensor or the like. As a result, the total production cost of the paper feeder

2

can be reduced.

The lock

34

engaged with the ratchet pawl

32

c

of the ratchet gear

32

restricts the forward rotation of the ratchet gear

32

. By this restriction, the push plate

24

is prevented from moving up and is halted at the plate standby position.

In addition, the lock

34

permits the reverse rotation of the ratchet gear

32

while restricting the forward rotation thereof. In other words, the lock

34

permits downward movement of the push plate

24

while preventing upward movement of the push plate

24

. The release cam

42

a

of the coupled cam

42

, which is rotated in response to the rotation of the sheet feed roller

7

, can release the lock

34

from the engagement with the ratchet gear.

The speed at which the push plate

24

is urged by the elastic spring

25

and moved up to the plate upper position is attenuated by the attenuator

31

. This reduces the impact of a stack of sheets P on the pressure plate

6

with the sheet feed roller

7

. Thus, a stack of sheets P on the pressure plate

6

is prevented from colliding violently with the sheet feed roller

7

, and impact noise generated during upward movement of the push plate

24

is reduced.

Upon the insertion of the sheet feed cassette

4

into the cassette inserting section

1

b

, the push-up plate

4

f

makes the elastic spring

25

start generating an urging force. Before the insertion of the sheet feed cassette

4

, the push plate

24

is prevented from being urged by the elastic spring

25

. Thus, before the insertion of the sheet feed cassette

4

, the push plate

24

is not affected by any urging force or load. Accordingly, an aged creep of the push plate

24

can be prevented.

The elastic spring

25

for urging the push plate

24

is made of an elastic material having restorable elasticity. Thus, no device, such as a motor, is required for applying an urging force to the push plate

24

, and the total production cost of the sheet feeder

2

can be reduced.

While the invention has been described in connection with a preferred embodiment thereof, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, various changes may be made without departing from the spirit and scope of the invention. Although in the above-described embodiment, the sheet feeder

2

according to the invention is applied to the printer

1

as an image forming device, the invention may be applied to a document feeder mounted on an image reader.

Number	Name	Date	Kind
5078380	Kitazawa	Jan 1992	A
5228676	Arai et al.	Jul 1993	A
5419543	Nakamura et al.	May 1995	A
6059282	Jang	May 2000	A

Sheet feeder

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (1)

US Referenced Citations (4)

Foreign Referenced Citations (1)