JPH0228997B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a thread cutting device for a sewing machine.

[Conventional technology]

A conventional thread cutting device includes a fixed knife F and a movable knife M, and cuts threads in the following manner.

(1) When the movable knife moves forward When the movable knife M rotates clockwise in Fig. 2a, the separating section M1 separates the threads to be sheared (bobbin thread L and thread UT on the fabric side) and the threads not to be sheared (needle thread). The side needle thread UN) is separated, and the unsheared thread is moved clockwise while being hooked to the hook M2, while the separated thread to be sheared is moved by the moving scalpel. During the rotation of M, it is strongly pressed outward by the circular arc portion M3 of the moving scalpel M and bent into a dogleg shape, and then the outward pressure is removed at the end of the circular arc portion M3. Then, due to the tension of this thread, this thread suddenly moves to the blade portion M4 (see Fig. 2b).

(2) When the movable knife moves back When the movable knife M rotates counterclockwise in Fig. 2b, the thread to be sheared is moved in the direction of the fixed knife F while being held by the blade M4, and this fixed knife Sheared by F and moving scalpel M.

[Problem that the invention seeks to solve]

However, among the threads to be sheared that are in contact with the circular arc part M3 of the moving knife, the needle thread UT on the cloth side is
Due to the frictional resistance of
Among the threads to be sheared, the tension of the bobbin thread L that comes into contact with thread 3 may loosen the bobbin thread tension by the bobbin case, or may become insufficient depending on the type of thread.
Even when the moving knife M rotated, it remained bent in a dogleg shape and did not slide on the arcuate portion M3.

For this reason, in either case, there was a problem in that the thread to be sheared was not held in the blade portion M4, and thread cutting was not performed.

[Means for solving problems]

In this invention, during the forward movement of the moving knife, the thread to be sheared is held by a thread pulling mechanism, and at the maximum forward movement position of the moving knife, it is held on the movement trajectory of the blade portion of the moving knife, This allows for reliable thread cutting.

〔Example〕

An embodiment of the invention will be described based on FIG.
In the figure, 1 is a fixed scalpel, the base of which is fixed to the machine frame with screws, and the blade 1 facing the needle hole NH.
A is provided. 2 is a movable scalpel whose base is rotatably supported by a screw. The outer end of the movable scalpel 2 is formed into an arc shape, and one side thereof has a blade portion 2a opposite to the blade portion 1a of the fixed knife 1.
is provided, and the other side is cut out to form a hook part 2.
b and a separating section 2c are formed. Reference numeral 3 denotes an arm whose center part is supported by a screw, one end of which is connected to the movable scalpel 2 via an arm 4, and the other end is brought into contact with a cam (not shown) via a connecting rod 5. There is. Reference numeral 6 denotes a thread shifting plate, one end of which is rotatably supported by a screw, and a guide groove 6b in the shape of an "E" is formed at the base. Its sides are
A protrusion 6 is placed opposite the thread to be sheared immediately before thread cutting.
A is provided at the tip of the protrusion 6a, and the tip of the protrusion 6a is cut out to form a recess in order to hold the thread to be sheared immediately before the thread cutting. A pin mounting base 7 is fixed to the connecting rod 5 with a screw, and a pin 7a provided on the pin mounting base 7 is guided through a guide groove 6b of the thread shifting plate 6.

The connecting rod 5, the thread shifting plate 6, the pin mounting base 7, the pin 7a, etc. constitute a thread shifting mechanism.

Next, the effect will be explained.

(a) When the movable knife moves forward When the movable knife 2 rotates counterclockwise in Fig. 1a, the separating section 2c separates the threads to be sheared (lower thread L and thread UT on the fabric side) and the threads not to be sheared ( The needle thread (UN) on the needle side is separated. The unsheared thread that is not to be sheared is moved counterclockwise while being hooked to the hook portion 2b, while the thread that is to be sheared is moved between the outer end of the movable scalpel 2 and the protrusion of the arm 6. located between the parts 6a (FIG. 1b)
reference).

Then, when the movable knife 2 further rotates counterclockwise, the thread to be sheared is removed from the protrusion 6a.
The blade portion 2a of the movable scalpel 2 is moved along the movement trajectory while being held at the same position (see FIG. 1c).

(b) When the movable knife moves back When the movable knife 2 is rotated clockwise in Fig. 1c, the thread to be sheared is moved in the direction of the fixed knife 1 while being held by the blade part 2a; It is sheared by the fixed knife 1 and the moving knife 2.

Note that the above thread trimming device has been described for a lockstitch sewing machine that forms stitches with upper thread and lower thread.
This thread cutting device can also be applied to thread cutting devices for chain stitch sewing machines such as single chain stitch and double chain stitch sewing machines.

〔Effect of the invention〕

Since this invention has the above-described configuration, the yarn to be sheared can be held on the movement trajectory of the blade of the moving scalpel, and therefore, the yarn to be sheared can be reliably sheared. There is.

[Brief explanation of drawings]

FIGS. 1A, 1B, and 1C are diagrams showing an embodiment of the present invention and for explaining the thread cutting operation, and FIGS. 2A and 2B are diagrams for explaining the conventional thread cutting operation, respectively. In the figure, 1 is a fixed knife, 2 is a moving knife, 5 is a connecting rod, and 6 is a thread shifting plate.

Claims (1)

[Scope of Claims] 1. A fixed scalpel 1, the base of which is rotatable around a fixed axis, and which rotates in one direction in conjunction with the forward movement of the connecting rod 5 to separate the threads to be sheared and the threads not to be sheared. A movable scalpel 2 that rotates in the opposite direction in conjunction with the return movement of the connecting rod and shears the thread captured by the blade in cooperation with a fixed knife, and a base rotatable about a fixed axis. A yarn shifting plate 6 is provided which rotates in conjunction with the connecting rod and has a concave portion for capturing the yarn to be sheared, and when the connecting rod moves forward, the yarn to be sheared is captured in the concave portion of the yarn shifting plate 6. A thread cutting device for a sewing machine, characterized in that the thread is moved along the locus of movement of a blade of a movable knife 2.