Sewing – Stitch forming – Chain or double chain
Reexamination Certificate
2001-05-01
2002-06-11
Izaguirre, Ismael (Department: 3765)
Sewing
Stitch forming
Chain or double chain
Reexamination Certificate
active
06401640
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a sewing machine such as a multi-thread chain stitch sewing machine, covering sewing machine, safety stitch sewing machine, or the like to perform sewing by means of a needle that moves up and down while sticking into a cloth on a needle plate and a looper that projects and withdraws laterally under the needle plate.
The multi-thread chain stitch sewing machine has one needle or a plurality of needles that hold a needle thread and move up and down while sticking into a cloth on a needle plate. Furthermore, the multi-thread chain stitch sewing machine has a looper that holds a looper thread and projects and withdraws laterally under a needle plate. This multi-thread chain stitch sewing machine operates as follows. First, when a needle thread is sent out by a fall of the needle and the movement of the needle is converted into a rise, the multi-thread chain stitch sewing machine operates so that the looper catches the loop of the needle thread left under the needle plate in synchronization with this rise.
Second, the multi-thread chain stitch sewing machine draws out the loop of the needle thread caught by the looper upon feeding a cloth back or forth on the needle plate. Third, when changing the looper so as to withdraw, the multi-thread chain stitch sewing machine catches the loop of the looper thread left by the needle that moves down in synchronization with the withdrawal. The multi-thread chain stitch sewing machine repeats these operations in order.
The covering stitch sewing machine performs such sewing operation in the same manner. The safety stitch sewing machine performs over-edge chain stitching on the edge of a cloth, and at the same time, performs the abovementioned multi-thread chain stitching along one side of the over-edge chain stitch.
FIG.
3
and
FIG. 4
are plan views of the multi-thread chain stitches viewed from the back surface side of a cloth to be sewn. As shown in the figures, the looper thread
20
is caught in the loop of needle thread
10
that is exposed to the back surface of the cloth W at predetermined intervals corresponding to the amount of movement of the cloth W.
In the figures, the white arrows with black outlines show the direction of feeding of the cloth W. The needle thread
10
and looper thread
20
are intertwined with each other at a stitch by inserting the looper thread
20
into one loop (rear loop) of the needle thread
10
from the rear side of the direction of feeding. Then, the intertwined portion is passed through the front portion of the loop (front loop) adjacent to the rear loop and returned to the rear side. Thereafter, the intertwined portion is inserted into the rear loop again and turned back. Last, the intertwined portion is inserted into the front loop from the rear side of the direction of feeding. These processes are repeated, and then the intertwined portions form double rings formed of the looper thread
20
across the front loop and rear loop that are formed of needle thread
10
adjacent to each other in the direction of feeding.
The difference between the stitches shown in FIG.
3
and
FIG. 4
arises due to the balance in tension between the needle thread
10
and looper thread
20
. In the case where the tension of the needle thread
10
is increased to be greater than that of the looper thread
20
, due to the tension of the needle thread
10
toward the surface side of the cloth W, the inserted portion of the looper thread
20
is strongly tightened. As a result, as shown in
FIG. 3
, a stitch in which the double rings stretch between the rear loop and front loop of the needle thread
10
is obtained.
To the contrary, in the case where the tension of the needle thread
10
is weakened to be less than that of the looper thread
20
, the looper thread
20
is pulled against the relatively week tightening by the needle thread
10
. As a result, as shown in
FIG. 4
, the double rings formed of the looper thread
20
stretch between the rear loop and front loop of the needle thread
10
and form a stitch in which the double rings overlap each other.
Such a form of stitches is selected depending on the kind of the cloth W to be sewn and sewing conditions such as a sewing portion. For example, to sew a thick cloth with high rigidity such as denim or the like, the stitch shown in
FIG. 4
is selected in many cases in order to realize firm sewing without looseness. On the other hand, to sew a thin cloth with flexibility such as a cloth for a shirt, the stitch shown in
FIG. 3
is selected in order to obtain a smooth texture.
However, to obtain the stitch shown in
FIG. 3
, as mentioned above, the tension of the needle thread
10
must be increased to be greater than that of the looper thread
20
. If this is realized by increasing the tension of the needle thread
10
, the cloth itself is tightened due to the high tension of the needle thread
10
. Then, surface wrinkles called puckering occurs on the cloth after being sewn. Thereby, the finishing quality deteriorates.
To the contrary, in the case where the stitch is realized by reducing the tension of the looper thread
20
, the looper thread sent out by the looper become loose. Then, it fails to catch the looper thread
20
when the needle moves down. Thereby, skip stitch occurs and the finishing quality deteriorates.
In order to solve the above problems and stably obtain the stitch shown in
FIG. 3
, a sewing machine provided with a retainer needle has been conventionally made practicable. This retainer needle is mounted together with a sewing needle to the needle bar so as to be positioned closer to the projection side of the looper than the sewing needle. The retainer needle reaches the position under the needle plate prior to the sewing needle when the needle bar moves down. On the other hand, the retainer needle comes out from the position under the needle plate after the sewing needle when the needle bar moves up.
According to this construction, the looper thread
20
sent out by the projection of the looper is caught by the retainer needle which reaches the position under the needle plate prior to the needle at the projection side of the looper ahead of the needle (in the case where a plurality of needles are provided, outside the outermost needle). The needle moves up in synchronization with the next projection of the looper, and this catch is maintained until the tightening by the needle thread
10
is started. This result is shown in FIG.
3
. Between the front and rear loops of the needle thread
10
to be exposed to the back surface of the cloth W, the double rings of the looper thread
20
gradually spread. Then, a stitch is stably formed. It becomes unnecessary to adjust the tension of the needle thread
10
and looper thread
20
. Furthermore, sewing failures such as the abovementioned puckering and skip stitch do not occur.
Thus, the sewing machine with a retainer needle has a simple structure in which the retainer needle is only attached to the needle bar for moving the needle up and down. In addition, the sewing machine with a retainer needle can stably perform multi-thread chain stitching (including safety stitching) or covering stitching regardless of the kind of the sewing cloth.
However, the retainer needle is constructed so as to reach the position under the needle plate by penetrating the cloth W together with the needle to catch the looper thread
20
. When sewing by such a sewing machine with a retainer needle, as shown in
FIG. 3
, holes H, H . . . caused by penetration of the retainer are formed in line along one side of the multi-thread chain stitch (the projection side of the looper). Therefore, for uses requiring high finishing quality, the existence of these holes comes into question.
Recently, in order to make ironing after washing unnecessary, sewn products (such as shirts, handkerchiefs, and others) using shape-memory cloth have been made practicable. In the case where a sewing machine with a retainer needle is used for sewing each portion of such
Izaguirre Ismael
Yamato Mishin Seizo Kabushiki Kaisha
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