US20090020056A1

US20090020056A1 - Cloth presser device of sewing machine

Info

Publication number: US20090020056A1
Application number: US12/173,837
Authority: US
Inventors: Shuuji FUJITA
Original assignee: Juki Corp
Current assignee: Juki Corp
Priority date: 2007-07-17
Filing date: 2008-07-16
Publication date: 2009-01-22
Also published as: JP2009022352A

Abstract

A cloth presser device of a sewing machine is provided. The cloth presser device includes a presser bar, a presser foot rotatably supported by the presser bar at an intermediate portion of the presser foot in a cloth feeding direction, an auxiliary presser rotatably coupled to the presser foot on an upstream side, in the cloth feeding direction, of a point at which the presser bar supports the presser foot, the auxiliary presser having a cloth pressing portion which presses a cloth on a downstream side of a portion of the auxiliary presser coupled to the presser foot, and a front presser spring attached to the presser bar and downwardly biasing the cloth pressing portion. A point at which the front presser spring presses the auxiliary presser is on a downstream side of the portion of the auxiliary presser coupled to the presser foot.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority from Japanese Patent Application No. 2007-185705 filed on Jul. 17, 2007, the entire content of which is incorporated herein by reference.

FIELD OF INVENTION

The present invention relates to a cloth presser device of a sewing machine.

DESCRIPTION OF RELATED ART

Related art sewing machines include a presser bar which is vertically movable, a presser foot which is rotatably attached to a lower end of the presser bar to press a cloth from above, and an adjustable presser bar spring which biases the presser bar to press the presser foot onto a throat plate.
The presser foot is disposed above a feed dog, and presses the cloth such that the feed dog can feed the cloth in a cloth feeding direction. The presser foot is coupled to the presser bar at an intermediate portion in a base end portion thereof. Therefore, a pressing force from the presser bar is smoothly transmitted to the base end portion of the presser foot, but is not much transmitted to a front end portion of the presser foot. Accordingly, the pressing force applied from the front end portion of the presser foot to the cloth is weak.
In view of above, a related art cloth presser device includes a front presser spring which presses the front end portion of the presser foot from above (see, e.g., JP 3866096 B2). More specifically, the pressing force from the presser bar is transmitted to the front end portion of the presser foot through the front presser spring. According to such a cloth presser device, therefore, the presser foot can press the cloth with both the base end portion and the front end portion thereof.
In the cloth presser device described above, the front presser spring directly presses the front end portion of the presser foot to ensure sufficient pressing force toward the cloth. While the pressing force to be applied to the cloth needs to be strong enough to prevent the cloth from unnecessarily being moved, it is also required to allow a stepped portion of the cloth to be smoothly fed beneath the front end portion of the presser foot. However, if the pressing force is set to be strong enough to prevent the cloth from unnecessarily being moved in the related art cloth presser device, there has been a problem that a stepped portion or the like of the cloth becomes stuck on the front end portion of the presser foot, which results in a defective sewing. On the other hand, if the pressing force from the presser bar is set to be weaker in order to prevent such a defective sewing, there has been a problem that the pressing force on the base end portion of the presser foot becomes insufficient to firmly press the cloth.

SUMMARY OF INVENTION

It is an object of the present invention is to provide a cloth presser device which can firmly press a cloth with both a front end portion and a base end portion of a presser foot, while preventing a defective sewing.
According to an aspect of the present invention, a cloth presser device of a sewing machine is provided. The cloth presser device includes: a presser bar supported by a frame of the sewing machine so as to be vertically movable, and is biased downward; a presser foot rotatably supported by the presser bar at an intermediate portion of the presser foot in a cloth feeding direction; an auxiliary presser rotatably coupled to the presser foot on an upstream side, in the cloth feeding direction, of a point at which the presser bar supports the presser foot, the auxiliary presser having a cloth pressing portion which presses a cloth on a downstream side, in the cloth feeding direction, of a portion of the auxiliary presser coupled to the presser foot; and a front presser spring attached to the presser bar and having one end portion downwardly biasing the cloth pressing portion, wherein a point at which the front presser spring presses the auxiliary presser is on a downstream side, in the cloth feeding direction, of the portion of the auxiliary presser coupled to the presser foot.
According to another aspect of the invention, a cloth presser device includes: a presser bar; a presser foot; a first coupling portion rotatably coupling a lower end portion of the presser bar and a presser foot; a first auxiliary presser having a cloth pressing portion; a second coupling portion rotatably coupling the presser foot and the first auxiliary presser; and a front presser spring comprising one end portion downwardly pressing the cloth pressing portion and the other end portion attached to the presser bar; wherein, in a cloth feeding direction, a pressing point at which the one end portion of the front presser spring presses the cloth pressing portion is on a downstream side of the second coupling portion, the cloth pressing portion presses a cloth on a downstream side of the pressing point, and the first coupling portion is disposed on a downstream side of the cloth pressing portion.
Other aspects and advantages of the invention will be apparent from the following description, the drawings and the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a cloth presser device of a sewing machine according to an exemplary embodiment of the invention;

FIG. 2 is a plan view of the cloth presser device;

FIG. 3 is a side view of the cloth presser device;

FIG. 4 is a diagram for explaining a pressing force applied onto an auxiliary presser;

FIG. 5 is another diagram for explaining of a pressing force applied to the auxiliary presser; and

FIG. 6 is another diagram for explaining of a lifting force applied to a front presser spring.

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment of the invention will be explained with reference to the drawings. The following exemplary embodiment does not limit the scope of the invention.
As shown in FIGS. 1 to 3, a cloth presser device 1 of a sewing machine (hereinafter “cloth presser device 1”) is disposed below needles N of the sewing machine, and includes a presser bar 2, a presser foot 3 rotatably coupled to the presser bar 2, a hinge portion 31 (a first coupling portion) coupling the presser bar 2 and the presser foot 3 at an intermediate portion of the presser foot 3 in a longitudinal direction of the presser foot 3 (i.e., an intermediate portion in a cloth feeding direction A shown in FIG. 1), an first auxiliary presser 4 having a cloth pressing portion 42, a hinge portion 42 (a second coupling portion) coupling the presser foot 3 and the first auxiliary presser 4, a front presser spring 5 having one end attached to the presser bar 2 to downwardly press the cloth pressing portion 42 of the first auxiliary presser 4 with the other end, a second auxiliary presser 6, and a hinge portion 61 (a third coupling portion) coupling the presser foot 3 and the second auxiliary presser 6. The presser bar 2 is supported by a frame of a sewing machine so as to be vertically movable, and is downwardly biased. When seen in the cloth feeding direction A, the first auxiliary presser 4 is rotatably coupled to the presser foot 3 via the coupling portion 42 on an upstream side of the coupling portion 31, while the second auxiliary presser is rotatably coupled to the presser foot 3 via the coupling portion 61 on a downstream side of the coupling portion 31.
A hook 21 is fixed to a lower end of the presser bar 2 with a screw or the like, and is engaged with the hinge portion 31 whereby the presser bar 2 and the presser foot 3 are rotatably coupled to each other.
Although the presser bar 2 is coupled to the intermediate portion of the presser foot 3 in the cloth feeding direction A (around a center of the presser foot 3) via the hinge portion 31 and the hook 21, the presser bar 2 is inclined toward a side of a base end portion of the presser foot 3, and a pressing force from the presser bar 2 is applied primarily to the base end portion of the presser foot 3. In order to feed the cloth with a feed dog 10 projecting from a throat plate T, a lower surface of the presser foot 3 is flat and presses the cloth such that the cloth is not unnecessarily moved during a sewing operation. A front end portion of the presser foot 3 is formed to be upwardly curved so that a stepped portion of the cloth is smoothly guided beneath the presser foot 3 at the time of feeding the cloth.
A central portion of the first auxiliary presser 4 in a longitudinal direction thereof is rotatably coupled to the front end portion of the presser foot 3 via the hinge portion 41.
One end of the first auxiliary presser 4 is arranged along the curved portion of the front end portion of the presser foot 3, while the other end (i.e., the cloth pressing portion 42) of the first auxiliary presser 4 is arranged to project downward from a through-hole formed in a central portion of the presser foot 3 to press the cloth.
The front presser spring 5 is a wirily formed elastic spring, and one end thereof is attached to the presser bar 2. The front presser spring 5 is arranged to extend from the presser bar 2 toward the front end portion of the presser foot 3, and the other end thereof is disposed so as to be in contact with the first auxiliary presser 4 at a position between the hinge portion 41 and the cloth pressing portion 42. That is, the front presser spring 5 presses the first auxiliary presser 4 at the position between the hinge portion 41 and the cloth pressing portion 42 with its other end, i.e., when seen in the cloth feeding direction A, a pressing point 43 at which the front presser spring 5 presses the first auxiliary presser 4 is on the downstream side of the hinge portion 41. Accordingly, the pressing force from the presser bar 2 is transmitted to the first auxiliary presser 4 via the front presser spring 5, whereby the first auxiliary presser 4 rotates around the hinge portion 41 and the cloth pressing portion 42 presses the cloth.
A lower surface of the second auxiliary presser 6 toward both the upstream side and the downstream side from the hinge portion 31, which is the coupling portion between the presser bar 2 and the presser foot 3. The second auxiliary presser 6 is coupled to the presser foot 3 via the hinge portion 61 which is positioned on the downstream side of the hinge portion 31.
The second auxiliary presser 6 is rotatably attached to the hinge portion 61. More specifically, a portion of the second auxiliary presser 6 on the upstream side of the hinge portion 61 abuts on the presser foot 3 when a lower surface of the second auxiliary presser 6 is in plane with a lower surface of the presser foot 3, and from that position, the second auxiliary presser 6 is rotatable around the hinge portion 61 until the portion of the second auxiliary presser 6 on the upstream side of the hinge portion 61 becomes lower than the lower surface of the presser foot 3 by a certain amount. The second auxiliary presser 6 is arranged such that, when the pressing force is transmitted from the presser bar 2 to the second auxiliary presser 6 via the presser foot 3, the pressing force is applied to the cloth from the lower surface of the second auxiliary presser 6.
Next, the operations of the cloth presser device 1 will be described with reference to FIGS. 4 to 6.
As shown in FIG. 4, when the pressing force F from the presser bar 2 is increased, i.e., when the pressing force F is applied to the presser bar 2 by elastic force of the spring which biases the presser bar 2, the pressing force F is transmitted to the presser foot 3 via the hinge portion 31. Because the second auxiliary presser 6 is provided to the presser foot 3, the base end portion of the presser foot 3 presses down the cloth in advance of the front end portion thereof.
In FIG. 4, L1 is a horizontal distance between the hinge portion 31 and the hinge portion 61 in a state in which the lower surface of the second auxiliary presser 6 is in contact with the cloth, L2 is a distance between the hinge portion 61 and a front end of the presser foot 3, L3 is a horizontal distance between the hinge portion 41 and the pressing point 43, and L4 is a horizontal distance between the hinge portion 41 and the cloth pressing portion 42.
As shown in FIG. 4, F×L1=L2×F1 wherein F1 is a pressing force at the front end of the presser foot 3. Thus, the pressing force F1=L1/L2×F is applied to the front end portion of the presser foot 3. That is, the pressing force applied to the front end portion of the presser foot 3 is less than the pressing force applied to the base end portion of the presser foot 3, and in order to increase pressing force to be applied to the front end portion of the presser foot 3 without the front presser spring 5, it is necessary to increase the pressing force F. However, when introducing a pressing force f to be applied to the front presser spring 5 from the presser bar 2 into consideration, f×(L4−L3)=L4×f1 wherein f1 is a pressing force at the hinge portion 41. That is, the pressing force f1=(L4−L3)/L4×f is applied from the hinge portion 31 to the hinge portion 41 via the first auxiliary presser 4. The pressing force f1=(L4−L3)/L4×f is applied only to the front end portion of the presser foot 3 owing to the front presser spring 5. Therefore, the total pressing force of L1/L2×F+(L4−L3)/L4×f is applied to the front end portion of the presser foot 3. Therefore, by providing the front presser spring 5, it is possible to compensate for the lack of pressing force at the front end portion of the presser foot 3 without increasing the pressing force F from the presser bar 2.
When the first auxiliary presser 4 completely laid down as shown in FIG. 5, i.e., when the entire lower surface of the presser foot 3 is able to press the cloth, the pressing force f from the front presser spring 5 is applied entirely to the first auxiliary presser 4, and a pressing force of L1/L2×F+f is applied to the front end portion of the presser foot 3.
On the other hand, as shown in FIG. 6, when a stepped portion of the cloth is fed into a lower side of the presser foot 3, a force M to lift up the front end portion of the presser foot 3 is applied to the presser foot 3.
In FIG. 6, L5 is a horizontal distance between the hinge portion 41 and the pressing point 43, L6 is a horizontal distance between the hinge portion 41 and the cloth pressing portion 42, and L7 is a distance between the cloth pressing portion 42 and the hinge portion 61.
When assuming that a lifting force m is applied to the first auxiliary presser 4 from the presser foot 3, and taking into consideration the front presser spring 5 which presses the first auxiliary presser 4 from above, L5×f=L6×α which leads to α=L5/L6×f. Thus, the front presser spring 5 creates a moment M=α×L7=L5/L6×L7×f which lifts up the front end of the presser foot 3. As a result, it is possible to lift up the presser foot 3 with a force that is less than the pressing force f of the front presser spring 5.
According to the cloth presser device 1 described above, when the pressing force is applied to the presser bar 2, the pressing force also acts to the front presser spring 5 attached to the presser bar 2, and the front presser spring 5 presses the first auxiliary presser 4 downward.
At this time, because the pressing point 43 at which the front presser spring 5 presses the first auxiliary presser 4 is on the downstream side of the hinge portion 41 in the cloth feeding direction, a force required to lift up the front end portion of the presser foot 3 is less than that in a case where the front presser spring 5 directly presses the presser foot 3.
That is, when the entire lower surface of the presser foot 3 presses the cloth, the pressing force f from the front presser spring 5 is applied entirely to the first auxiliary presser 4, and the pressing force of L1/L2×F+f is applied to the front end portion of the presser foot 3.
On the other hand, when lifting up the presser foot 3, the moment of L5/L6×L7×f which lifts up the front end portion of the presser foot 3 is generated by the front presser spring 5. Thus, it is possible to lift up the front end portion of the presser foot 3 with a smaller force.
Further, by providing the second auxiliary presser 6, when the pressing force is applied to the presser bar 2, the pressing force is applied to the second auxiliary presser 6 via the presser foot 3. Because the presser foot 3 is rotatable around the hinge portion 61 with respect to the second auxiliary presser 6, the pressing force applied to the front end portion of the presser foot 3 is reduced. On the other hand, sufficient pressing force from the base end portion of the presser foot 3 to the cloth is ensured by the second auxiliary presser 6. Further, the pressing force to be applied to the front end portion of the presser foot 3 is not as strong as that applied to the base end portion of the presser foot 3.
Therefore, even when the pressing force from the presser bar 2 is increased, the pressing force to be applied to the front end portion of the presser foot 3 is adequately reduced.
Consequently, it is possible to press the cloth with both the front end portion and the base end portion of the presser foot 3, while allowing the front end portion of the presser foot 3 to be lifted up with a small force to prevent a defective sewing.
While description has been made in connection with the exemplary embodiment of the present invention, those skilled in the art will understand that various changes and modification may be made therein without departing from the present invention. It is aimed, therefore, to cover in the appended claims all such changes and modifications falling within the true spirit and scope of the present invention.

Claims

1. A cloth presser device of a sewing machine, the cloth presser device comprising:

a presser bar supported by a frame of the sewing machine so as to be vertically movable, and is biased downward;

a presser foot rotatably supported by the presser bar at an intermediate portion of the presser foot in a cloth feeding direction;

an auxiliary presser rotatably coupled to the presser foot on an upstream side, in the cloth feeding direction, of a point at which the presser bar supports the presser foot, the auxiliary presser comprising a cloth pressing portion which presses a cloth on a downstream side, in the cloth feeding direction, of a portion of the auxiliary presser coupled to the presser foot; and

a front presser spring attached to the presser bar and having one end portion downwardly biasing the cloth pressing portion,

wherein a point at which the front presser spring presses the auxiliary presser is on a downstream side, in the cloth feeding direction, of the portion of the auxiliary presser coupled to the presser foot.

2. A cloth presser device of a sewing machine, the cloth presser device comprising:

a presser bar;

a presser foot;

a first coupling portion rotatably coupling a lower end portion of the presser bar and a presser foot;

a first auxiliary presser comprising a cloth pressing portion;

a second coupling portion rotatably coupling the presser foot and the first auxiliary presser; and

a front presser spring comprising one end portion downwardly pressing the cloth pressing portion and the other end portion attached to the presser bar,

wherein, in a cloth feeding direction,

a pressing point at which the one end portion of the front presser spring presses the cloth pressing portion is on a downstream side of the second coupling portion,

the cloth pressing portion presses a cloth on a downstream side of the pressing point, and

the first coupling portion is disposed on a downstream side of the cloth pressing portion.

3. The cloth presser device according to claim 2, wherein the presser bar is supported by a frame of the sewing machine so as to be vertically movable, and is biased downward.

4. The cloth presser device according to claim 2, further comprising:

a second auxiliary presser; and

a third coupling portion rotatably coupling the presser foot and the second auxiliary presser,

wherein, in the cloth feeding direction, the third coupling portion is disposed on a downstream side of the first coupling portion.

5. The cloth presser device according to claim 2, wherein the front presser spring and the first auxiliary presser are arranged and configured to create a moment which acts on the presser foot in a direction in which a portion of the presser foot on an upstream side, in the cloth feeding direction, of the first coupling portion upwardly rotates.

6. The cloth presser device according to claim 2, wherein the first auxiliary presser is rotatable such that the cloth pressing portion becomes lower than a lower surface of the presser foot.

7. The cloth presser device according to claim 4, wherein, when pressing the cloth, a lower surface of the second auxiliary presser is always in contact with the cloth.

8. The cloth presser device according to claim 7, wherein, when the lower surface of the second auxiliary presser is in plane with a lower surface of the presser foot, a portion of the second auxiliary presser on an upstream side, in the cloth feeding direction, of the third coupling portion abut on a presser foot.