Apparatus for detecting thread breakage in sewing machine

Sewing – Elements – Starting or stopping

Reexamination Certificate

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Details

C112S248000

Reexamination Certificate

active

06213039

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for detecting breakage of a looper thread by monitoring vibration generating in looper thread along with driving of a sewing machine when forming a double-chain stitch in a cloth by the sewing machine.
2. Description of the Prior Art
In an ordinary conventional sewing machine comprising a needle moving up and down to penetrate through a needle hole of a needle plate, and a looper reciprocating laterally across the leading end of this needle, for forming a double-chain stitch by collaboration of the needle and looper, usually, a thread-controlling cam varying in the extent of projection from the thread take-up stand according to the rotation of the rotary shaft such as main shaft is disposed between two thread guides having a thread eyelet for inserting the looper thread, and the looper thread slides on the peripheral surface of this thread-controlling cam, so that it is designed to control the thread take-up extent.
In the sewing machine having such constitution, however, if the thread is broken during sewing operation, or if the thread is loose when driving the sewing machine again right after cutting off the thread before sewing operation or after sewing operation, the looper thread may wind around the rotary shaft of the thread-controlling cam. If driving of the sewing machine is continued without noticing the winding of looper thread around the rotary shaft of the thread-controlling cam, the looper thread is drawn out from the supply source side, and the winding amount on the rotary shaft increases progressively, and it takes much time and labor for removing the thread winded around the rotary shaft, which may cause to lower the sewing operation efficiency extremely. In particular, in the narrow tube bed sewing machine for sewing a tubular cloth, since the space in the narrow tube bed is small, it is very difficult to remove the thread winded around the rotary shaft.
SUMMARY OF THE INVENTION
The present invention is devised in the light of such circumstances, and it is hence an object thereof to provide an apparatus for detecting thread breakage in a sewing machine capable of detecting securely breakage of looper thread while driving the sewing machine, stopping driving of the sewing machine promptly, and blocking drop of sewing operation efficiency effectively.
The apparatus for detecting thread breakage in a sewing machine on the present invention is used in a sewing machine (
1
) comprises a needle (
2
) moving up and down to penetrate through a needle hole of a needle plate (
8
), a looper (
3
) reciprocating laterally across the leading end of the needle (
2
), a thread take-up stand (
10
) mounted on a sewing machine bed (l
a
), a thread-controlling cam (
11
) fixed on a rotary shaft (S) interlocked with the reciprocal motion of the looper (
3
), and varying in the extent of projection from the thread take-up stand (
10
) according to rotation of the rotary shaft (S), and a thread guide (
12
) disposed on the thread take-up stand (
10
) at both sides of the thread-controlling cam (
11
) and having a thread eyelet (
12
a
) for inserting the looper thread (
6
). Said apparatus comprises a pair of thread guides (
15
), (
15
) having thread pass eyelets (
15
a
) for inserting the looper thread (
6
) fixed and disposed on the looper thread route between the thread-controlling cam (
11
) and the looper (
3
), a thread breakage-detecting member (
13
) for detecting presence or absence of vibration of looper thread part (
6
a
) inserted in the thread pass eyelets (
15
a
), (
15
a
) of the pair of thread guides (
15
), (
15
) between the two thread guides (
15
) and (
15
), and a control circuit (
17
) for stopping driving of the sewing machine (
1
) on the basis of the detection of absence of thread vibration by this thread breakage-detecting member (
13
).
According to the present invention having such constitution, when the looper thread is consumed at the looper side, the looper thread taken up on the looper thread route through the thread eyelet in the thread guide and the peripheral surface of the thread-controlling cam is inserted into the thread pass eyelets of the pair of thread guides, and is guided into the looper. In the sewing operation by the sewing machine, while the looper thread taken up from the supply source side is normally guided toward the looper, a dynamic vibration is generated in the looper threads inserted into the thread pass eyelets in the pair of thread guides by the thread take-up control by the thread-controlling cam, whereas such vibration is not generated when the thread is broken.
Thus, by monitoring the presence or absence of vibration of looper thread guided into the looper as being inserted into the thread pass eyelets of the pair of thread guides fixed and disposed on the looper thread route between the pair of thread guides, breakage of looper thread can be detected securely without having effects of looper reciprocal motion or change of rotating speed of driving unit for the sewing machine, and driving of the sewing machine can be stopped promptly through the control circuit on the basis of the looper thread breakage-detecting. Therefore, not only the winding of the looper thread on the rotary shaft can be prevented, but also extra labor or time of removing the looper thread winded around the rotary shaft is unnecessary, so that the sewing operation efficiency may be enhanced extremely.
Other objects and effects of the invention will be clarified in the embodiment described below.


REFERENCES:
patent: 4429651 (1984-02-01), Tajima
patent: 4991528 (1991-02-01), Bellio

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