JPH0751177B2 - Thread trimming device for lockstitch sewing machine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thread trimming device that cuts an upper thread and a lower thread below a needle plate in a lockstitch sewing machine.

[Prior Art] Currently, a lockstitch sewing machine is provided with a thread trimming device that automatically performs a thread trimming operation after sewing is completed.
As the thread trimming device, the needle and the sewing machine hook perform a single sewing operation in response to a predetermined thread trimming command, and the movable blade moves horizontally between the needle plate and the sewing machine hook while passing through the sewing machine hook. It is generally known that a loop and a bobbin thread are caught and cut between a fixed blade. Usually, such a thread trimming device is provided with a leaf spring which is in contact with the head of the movable blade at the initial position of the reciprocating movement of the movable blade, and the end of the cut yarn is movable with the leaf spring. By sandwiching it with the blade, the lower thread is properly knotted with the upper thread loop in the next sewing.

[Problems to be Solved by the Invention] However, in the above-described conventional thread trimming device, when the sewn product exists on the needle drop point of the needle plate during the thread trimming operation, a relatively good thread trimming is performed. Although the operation is possible, when the thread trimming operation is performed with the sewn product taken out from the needle drop point (hereinafter, this thread trimming operation is referred to as drop trimming), the needle thread loop near the needle plate is Since the behavior becomes unstable, the thread length from the needle side upper thread end held by the leaf spring to the needle upper thread insertion hole after cutting becomes irregular, and the necessary and sufficient thread length cannot be obtained. was there. When such a shortage of thread length occurs, there is a problem in that the upper thread is pulled out from the needle thread insertion hole of the needle in the next sewing operation, resulting in poor sewing.

In addition, it is desirable that a certain amount of tension be applied to the thread caught by the movable blade at the time of cutting in order to improve the sharpness, but when the needle thread passes through the sewing machine hook, the upper thread moves from the needle side to the bottom of the needle plate. Since it is fed out to, there is a problem that tension is unlikely to be generated at the time of cutting and good sharpness cannot be obtained.

The present invention has been made in view of the above-mentioned problems, and the upper thread does not come out of the needle thread insertion hole of the needle even when performing drop-cutting, and an appropriate sewing state is always obtained, and
An object of the present invention is to provide a thread trimming device for a lockstitch sewing machine capable of obtaining a good sharpness of an upper thread.

[Means for Solving the Problem] According to the present invention, a movable blade is made to reciprocate once across a needle drop extension line in accordance with a predetermined thread cutting command, and a stitch of a lock stitch sewing machine and a sewing machine hook are formed. By performing the operation, the lower thread and the upper thread loop formed on the lower surface of the throat plate are caught by the movable blade, and both threads are cut at the same time between the movable blade and the fixed blade in sliding contact therewith. In a thread trimming device of a lockstitch sewing machine in which both of the thread ends are clamped between a movable blade and a leaf spring, an upper thread loop is formed on the upper thread loop contact surface of a bobbin case mounted in the sewing machine hook. And a thread hooking portion on a hook that can be fitted into the non-contact portion at the tip end, and the thread hooking portion is lateral to the sewing machine hook in conjunction with the reciprocating movement of the movable blade. Needle thread reciprocating from the above to the fitting position with the non-contact part A projecting member is provided.

[Operation] In the present invention, the needle thread drawing member reciprocates in conjunction with the reciprocating motion of the movable blade. At this time, the thread hooking portion provided at the tip of the needle thread drawing member is fitted into the non-contact portion formed on the front surface of the bobbin case with the needle thread and catches the needle thread passing there through to the side of the sewing machine hook. Return to. As a result, the needle thread path from the needle thread insertion hole of the needle to the movable blade is a path that is bent at the thread hooking portion as compared with the conventional straight path, and its length increases. Therefore, after cutting, the needle thread will not be pulled out from the needle thread insertion hole of the needle in the next sewing, and the sewing operation can be reliably performed. Also, due to the upper thread pulling operation of the upper thread pulling member, tension is generated in the upper thread at the time of cutting, so that good sharpness can be obtained.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings.

In FIGS. 1 and 2, reference numeral 1 denotes a known sewing machine hook provided below the needle plate B, which is an inner hook 2 that is locked to the machine frame of the sewing machine.
And an outer hook 3 rotatably fitted to the peripheral surface of the inner hook 2, and a bobbin case 4 in which a lower thread bobbin is housed is attached to the inner hook 2. A long groove 4a is formed on the front surface of the bobbin case 4 as a non-contact portion with the upper thread loop.

Reference numeral 6 denotes a thread cutting base fixed to the lower surface of the sewing machine head, and 7 denotes a moving base movably fitted in a guide groove 6a formed in the thread cutting base 6. This moving base 7 is always in the initial position shown in FIG. 2, and when a predetermined thread cutting command is input, it is connected to the lower shaft of the sewing machine through an interlocking mechanism, not shown, including the link member 5. While the lower shaft of the sewing machine makes one rotation together with the upper shaft of the sewing machine, the reciprocating motion is performed along the guide groove 6a by the interlocking mechanism using the rotational force as a driving force. Reference numeral 8 denotes a plate-shaped movable blade fixed to the upper surface of the moving table 7 with a screw 9, a hook-shaped thread catching portion 8a is formed at the tip thereof, and the upper surface of the thread catching portion 8a is further provided. The blade portion 8b is formed. 10 is the thread cutting base 6
Is a plate-shaped fixed blade fixed to the upper surface of the front end of the blade with a screw 11, and a blade portion 10a joined to the blade portion 8b of the movable blade 8 is formed at the tip portion thereof. 12 is the moving table 7 at the rear end
Is a leaf spring fixed to the lower surface of the movable table 8 with a screw 13, and its front end portion 12a is in pressure contact with the lower surface of the movable table 8.

Reference numeral 14 is a picker moving base fixed to the lower surface of the moving base 7 with a screw 15, and 16 is a picker fixed to the lower surface of the picker moving base 14 with a screw 17, and a tip end thereof has a long groove 4a of the bobbin case 4. A thread hooking portion 16a is formed which can be fitted in.

Next, the operation will be described based on the above configuration.

In the initial state before the thread cutting command is input, the movable table 7 is located rearward (to the right in the figure), and the thread catching portion 8a of the movable blade 8 is located.
Is held at the contact position between the fixed blade 10 and the leaf spring 12, that is, at the position retracted from the needle drop position. At this time, the thread hooking portion 16a of the picker 16 is located on the side of the sewing machine hook 1. Since the sewing operation is performed in this state, the needle and the sewing machine hook 1 are not obstructed by the movable blade 8 and the picker 16.

Now, when the sewing operation is completed and the thread trimming command is input, the upper shaft and the lower shaft of the sewing machine make one rotation, one sewing operation is performed by the needle and the outer hook 3, and the moving base 7 is moved to the guide groove 6a. It reciprocates once along the movable blade 8 and the picker 16 to reciprocate.

At this time, the movable blade 8 and the picker 16 are shown in FIGS. 3 (a) to (f).
The reciprocating operation is performed as shown in.

That is, the movable blade 8 moves horizontally from the initial position shown in FIG. 3A as shown in FIG.
And the sewing machine hook 1 and crosses the extension line L at the needle drop position. At this time, the tip of the movable blade 8 is caught by the sword tip 3a of the outer hook 3 and enters the upper thread loop I1 passing through the inner hook 2, and the two loop threads I1 _{1 of} the same loop I1, I1 ₂ to 3rd
Sort as shown in FIG. Thereafter, the movable blade 8 starts backward reaches the outermost forward position, at which slightly backward, loop yarn I1 ₁ and the lower thread I2 and the thread catching portion 8 sorting earlier
captured by a, backward to toward the initial position while pulling both thread I1 _2, I2 (see FIG. 3 (d)). Immediately before the movable blade 8 reaches the initial position, the captured yarns I1 ₁ , I2 are
The movable blade 8 is cut between the blade portion 8a and the fixed blade 10 of the blade portion 10a. As a result, the bobbin thread I2 is divided into a portion connected to the sewing machine hook 1 (hook side lower thread) I2a and a part connected to the sewn product (seam side bobbin thread) I2b, and the upper thread I1 is connected to the needle N ( Needle side upper thread) I1a and the part that continues to the sewn product (Stitch side upper thread) I
Divided into 1b. Then, when the movable blade 8 is completely returned to the initial position, the cut ends of the needle side upper thread I1a and the shuttle side lower thread I2a are clamped between the leaf spring 12 and the movable blade 8.

On the other hand, the picker 16 starts the reciprocating motion together with the movable blade 8 from the initial position shown in FIG. 3 (a), and when it moves a predetermined distance, as shown in FIG. 3 (b), as shown in FIG. Fit into the long groove 4a formed on the front surface of the bobbin case 4, and thereafter,
It moves forward along this long groove 4a. Then, among the needle thread passing through the bobbin case 2, the loop yarn I1 ₁ to move the front side of the bobbin case 4 is locked in contact with the yarn hooking portion 16a (see FIG. 3 (c)), the yarn I1 ₁ at the time of exit from the bobbin 2, is caught by the thread hook 16a so as to be in FIG. 3 (d). Then, the picker 16 returns with the movable blade 8 while holding the upper thread loop I1, and when the movable blade 8 cuts the thread,
Pull out the upper thread loop I1 to the side of the sewing machine hook 1 (see FIG. 3 (e)). As a result, the needle thread path from the movable blade 8 to the needle N is, as shown in FIG.
The path is bent at a, and the path length can be increased as compared with the conventional path without the picker 16 (shown by the one-dot chain line in FIG. 4). Therefore, even if the thread trimming operation is performed with the sewn product removed (even if the thread trimming is performed), the length from the needle thread insertion hole Na of the needle N to the needle thread cutting end is , The necessary length is maintained, so in the next sewing, the needle thread I1 is needle N
It does not come out of the upper thread insertion hole Na.

Further, by increasing the path length of the upper thread loop I1 by the picker 16 as described above, tension is generated in the upper thread loop I1 at the time of cutting, so that good sharpness can be obtained.

In the above embodiment, the long groove 4a is provided on the front surface of the bobbin case 4 to form the non-contact portion with the needle thread loop I1, but the non-contact portion may be a step portion instead of the long groove 4a. A through hole or the like may be provided.

Further, the thread trimming device according to the present invention can be applied to any sewing machine that performs a lock stitch operation, that is, a sewing machine that forms a stitch by knitting an upper thread loop and a lower thread by cooperation of a needle and a sewing machine hook. The present invention is applicable not only to sewing machines that form straight stitches, but also to sewing machines that perform zigzag stitches.

[Effect of the Invention] As described above, the thread cutting device according to the present invention captures and cuts the upper thread and the lower thread by the reciprocating motion of the movable blade, and draws the upper thread in conjunction with the operation of the movable blade. Since the member reciprocates and catches the upper thread loop passing through the front surface of the bobbin case and pulls it out to the side of the sewing machine hook, the upper thread from the needle to the movable blade at the time of cutting is the upper thread. The length of the path from the needle thread insertion hole to the needle thread cutting end of the needle is sufficiently maintained even if the needle is bent and cut off because it bends in the drawer member and the path length increases compared to the conventional device. Since the upper thread can be prevented from being pulled out from the needle at the time of the next sewing, the seam can be reliably formed.

Further, since the upper thread withdrawing member increases the path length of the upper thread loop, tension is generated in the upper thread captured by the movable blade at the time of cutting, so that the sharpness is extremely good.

[Brief description of drawings]

1 (a) is a plan view showing an embodiment of the present invention, FIG. 1 (b) is a side view of what is shown in FIG. 1 (a), and FIG.
Is a bottom view of what is shown in FIG. 2A. FIG. 2 is a perspective view showing the sewing machine hook and picker in the same embodiment, and FIG.
(F) is a perspective view showing an operating state of the movable blade and the picker in the same embodiment, and FIG. 4 is an explanatory side view showing a needle thread path at the time of cutting in the same embodiment and a conventional device. In the figure, 1 ... Sewing machine hook 4 ... Bobbin case 4a ... Long groove 8 ... Movable blade 8a ... Blade portion 10 ... Fixed blade 10a ... Blade portion 16 ... Picker (needle thread withdrawing member) 16a ... Thread hooking portion I1 ... Needle thread loop L ... extension line of needle entry position

Claims (2)

[Claims] 1. An intermediate position between the needle plate and the sewing machine hook,
Fixed with a movable blade that moves in a reciprocating path that crosses an extension line of the needle drop position from an initial position that is retracted horizontally from the needle drop position, and a blade portion that slides in contact with the blade portion of the movable blade at the initial position A blade and a leaf spring joined to one surface of the movable blade, the movable blade reciprocates in response to a predetermined thread cutting command, and a stitch forming operation by a needle of a lockstitch sewing machine and a sewing machine hook. The lower thread and the upper thread loop formed on the lower surface of the needle plate are caught by the movable blade, and both threads are cut between the movable blade and the fixed blade by cutting the both thread ends. A thread trimming device for a lockstitch sewing machine that is clamped between a movable blade and a leaf spring, wherein a non-contact portion with a needle thread loop is formed on the front surface of a bobbin case mounted in the sewing machine hook, and Hook that can be fitted into the stepped portion An upper thread withdrawing member that reciprocates between the side of the sewing machine hook and the fitting position into the non-contact portion in cooperation with the reciprocating movement of the movable blade. An upper thread loop passing through the front surface of the bobbin case is captured by the thread hooking portion fitted in the non-contact portion, and the captured upper thread loop is pulled out to the side of the sewing machine hook by returning the thread hooking portion. A thread trimming device for a lockstitch sewing machine, which is characterized in that 2. The thread trimming device of the lockstitch sewing machine according to claim 1, wherein the non-contact portion is a long groove formed on the front surface of the bobbin case along the moving direction of the thread hooking portion.