JPH0647184A - Sewing machine thread cutting device - Google Patents

Abstract

(57) [Abstract] [Purpose] In a thread cutting device of a sewing machine, two upper threads on the sewing side and the sewing needle side and a lower thread between the sewing object and the rotary hook are inserted through the rotary hook. Make sure there are no thread trimming defects that result in cutting. [Structure] A thread tension releasing means 7 which is provided between a balance of a sewing machine and a supply source of a sewing thread and which releases a thread tensioner 11 which applies thread tension to the sewing thread, and a fixed knife 5 which is located below the needle plate. A sewing machine including a cutting means 6 including a moving knife 4 that captures the sewing thread of the rotary hook 3 and the workpiece W and moves toward the fixed knife 5, and cuts the sewing thread with the fixed knife 5. The thread tension releasing means 7 of the thread cutting device is not driven until the moving knife 4 captures the sewing thread.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thread cutting device of a sewing machine, and more particularly, to two needle threads on the side of a sewing object and a side of a sewing needle via a rotary hook and between the sewing object and the rotary hook. The present invention relates to a thread cutting device for a sewing machine, which prevents a thread cutting failure that cuts a lower thread.

[0002]

2. Description of the Related Art A sewing machine is provided with a cutting device for cutting both upper and lower sewing threads on the cloth side at the end of sewing, and the thread cutting device of this sewing machine is installed below a needle plate.
A thread cutting device of a sewing machine includes a thread tension releasing means for releasing a main thread tension device provided between a balance of the sewing machine and a thread supply source, a fixed knife fixed to a sewing machine frame below a needle plate, and The cutting means is composed of a moving knife that moves toward the fixed knife, and is driven by a thread cutting signal.

The thread cutting device of the sewing machine drives the thread tension releasing means and the cutting means at the same time by the needle bar lower detection signal from the upper shaft angle detecting device for detecting the rotation angle of the upper shaft of the sewing machine to cut the sewing thread. I am supposed to do it. The operation when the sewing thread is cut by the thread cutting device of the sewing machine will be described with reference to FIG. FIG. 5 is a view showing a state in which the sewing needle N is in the raised position after the sewing is completed. In this state, the sewing needle W is rotated below the needle plate (not shown) as shown in the figure. The lower thread 2 between the hook 3 and the upper thread 1a, 1b which separates the workpiece W side and the sewing needle N side via the rotary hook 3 are located.

The thread cutting device of the sewing machine has a cutting means 6
The moving knife 4 is driven, the moving knife 4 is caught by the thread receiving groove 4a so as to insert the lower thread 2 and the upper thread 1a among the three sewing threads, and further moves toward the fixed knife 5. . When the moving knife 4 moves, the captured lower thread 2 and upper thread 1a move to the fixed knife 5 without being cut off because the thread tension regulator is in a released state, that is, in a loosened state. To do.

As a result, both sewing threads (bottom thread 2, upper thread 1a)
Is cut off, and the needle N can be left with the needle thread 1b of a length necessary for the start of the next sewing.

[0006]

However, the above-mentioned conventional techniques have the following problems. In the conventional thread cutting device for a sewing machine, as shown in FIG. 6, the moving knife 4 catches the upper thread 1b together with the lower thread 2 and the upper thread 1a, that is, the upper thread 1b portion is also cut. It causes inconvenience.

When such an inconvenience arises, the needle thread 1b having a proper length necessary for the next sewing does not remain on the sewing needle N, and therefore the needle thread is easily pulled up by the balance and it is impossible to continue the next sewing operation. Or, the cut pieces between the 1a portion and the 1b portion are left and adhere to the rotary hook 3, which enters the seams after the next sewing and impairs the appearance of the sewn product.

Incidentally, the cutting of these three sewing threads often occurs when the thread is cut by forming a reverse feed small pitch seam when performing stop stitching or the like as shown in Japanese Patent Laid-Open No. 1-230087.

The purpose of performing reverse feed small pitch stitches is to cut the sewing thread after the formation of normal stitches is completed.
As shown in FIG. 7, the thread remaining length of the workpiece W is equal to the upper thread 1
Compared to a, the lower thread 2 is longer by the stitch pitch, and the quality of the sewn product is deteriorated. Therefore, this is done to eliminate the difference in length between the two sewing threads.

FIG. 8 is a view showing the state of the sewing thread after the reverse feed small pitch stitches are formed. By forming the reverse feed small pitch stitches, as shown in the figure, the upper thread 1a and the lower thread from the work W are sewn. The cutting position of 2 can be adjusted, and a stable sewn product can be provided.

However, due to the formation of the reverse feed small-pitch seam, the sewing thread (bobbin thread 2, upper thread 1a, 1b) between the workpiece W and the rotary hook 3 has the upper thread 1 on the cloth side by the rotary hook 3. (1a) and the needle side (1b) are no longer separated, and as shown in the figure, they come close to each other, and the moving knife 4
At the time of driving, the moving knife 4 cannot properly handle these three sewing threads by the thread receiving groove 4a, so that the three cutting threads are caught and cut.

Further, the above-mentioned thread trimming failure is such that, at the time of thread cutting, the upper thread tension is applied only by the auxiliary thread tensioner arranged at the thread supply source by releasing the main thread tensioner. ,
If the tension of this auxiliary thread tension device is extremely low, a large amount of the upper thread will be supplied due to the inertia when the upper thread is hung by the hook. The three sewing threads are cut off.

[0013]

A thread cutting device for a sewing machine according to the present invention has been made to solve the above-mentioned conventional problems. A moving knife is provided with thread tension releasing means for the thread cutting device of the sewing machine. It is intended to solve the above-mentioned conventional problems by configuring so as not to drive until capturing.

[0014]

In the thread cutting device of the sewing machine according to the present invention, when the thread cutting signal is transmitted at the end of sewing, the moving knife of the thread cutting means is first driven to apply tension to the needle thread on the needle side. Capture the suture properly. After the moving knife has finished capturing the sewing thread, the tension of the sewing thread is released by the thread tension releasing means, and the loose sewing upper thread and bobbin thread are moved to the fixed knife by the driving knife and cut.

[0015]

Embodiments of the present invention will be described with reference to the drawings. The same parts as those of the conventional example are designated by the same reference numerals, and the duplicate description will be omitted. FIG. 1 is a block diagram showing a configuration state of a thread cutting device of a sewing machine.

As shown in the drawing, the thread cutting device of the sewing machine is connected through a control means B (CPU) to an upper shaft angle detecting device A for detecting the lower part of the needle bar by depressing the pedal of the sewing machine. It is designed to drive based on bottom detection. Then, the control means B first sends a thread cutting signal to the cutting means 6 by the needle bar down detection from the upper shaft angle detection device A, and then after the time t has elapsed from the needle bar down detection, the thread tension release means 7 is reached.
The drive signal is sent to.

The time t from the transmission of the thread cutting signal to the cutting means 6 to the transmission of the drive signal of the thread tension releasing means 7 is the time until the moving knife 4 of the cutting means 6 properly captures the sewing thread to be cut. Is set to. In this embodiment, when the angle of the upper shaft at the top dead center of the sewing needle of the sewing machine is set to 0 degree, the sewing needle is slightly raised from the bottom dead center of at least 21.
A thread cutting signal is sent to the cutting means 6 with 0 degrees (210 to 250 degrees) as the lower detection angle.

Then, when the moving knife 4 moves while applying tension to the upper thread to the position where the sewing thread is caught, when the upper axis angle reaches at least 300 degrees, a drive signal is sent from the control means B to the thread tension releasing means 7. It is configured to release the needle thread tension.

FIG. 2 is a view showing a constitutional state of the thread tension releasing means 7. In the figure, reference numeral 8 is a solenoid, which is fixed to the machine frame of the sewing machine and can be moved forward and backward by a drive signal from the control means B. It has become. Reference numeral 9 denotes a rotary plate rotatably supported on the sewing machine frame by a pin P, one end of which is connected to the solenoid 8 by a connecting rod 5, and the solenoid 8 is driven to move back and forth so as to be rotationally driven. There is.

On the other hand, 11 is a thread tension device of a sewing machine. This thread tension device includes two thread tension discs 12 for sandwiching a sewing thread, a spring B for applying a biasing force to the thread tension disc 12, and a thread tension disc 12.
13 and the separating plate 13 located between the spring and the spring B
Is provided with a push rod 14 that abuts on one end thereof. The other end of the rotary plate 9 of the thread tension releasing means 7 is provided with an inclined step portion 9a that comes into contact with the other end of the push rod 14 of the thread tension regulator 11 as shown in the figure.

The thread tension releasing means 7 sends a drive signal to the solenoid 8 to rotate the rotary plate 9 about the pin P as a fulcrum, and the tilted step portion 9a rotates clockwise to control the thread tension. The push rod 14 of the device 11 can be moved in the direction of the spring B to contract the spring B, that is, the upper thread (not shown) sandwiched between the thread tension discs 12 can be released.

Although the lower detection angle has a slight detection width, according to the result of the experiment, the thread cutting is performed by the cooperation of the fixed knife 5 and the moving knife 4 after receiving the thread cutting signal. Since it is approximately 150 ms, it has been proved that the time t should be at least 100 ms in consideration of a slight detection width.

Therefore, the solenoid 8 is controlled by the control means B.
The drive signal may be set to be transmitted at the time t described above. In this embodiment, the thread tension releasing means 7 is configured to be driven by electrical control, but the thread tension releasing means is connected to the thread cutting means 6 via, for example, a cam mechanism to drive the thread cutting means 6. On the other hand, the thread tension releasing means may be configured to drive the thread tension adjusting device at a predetermined timing so that the thread tension adjusting device is released.

In the thread cutting device of the sewing machine configured as described above, at the time of cutting the sewing thread, first, the thread cutting means 6 is driven, and as shown in FIG. The sewing thread in the state is properly handled, and only the sewing thread (the lower thread 2 and the upper thread 1a) to be cut is captured.

When the sewing thread (the lower thread 2 and the upper thread 1a) to be cut by the moving knife 4 has been dealt with, the thread tension releasing means 7 releases the thread tensioner 11 to release the loose sewing thread without tension. The blade is moved to the fixed knife 5 and cut by the blade portion of the fixed knife and the blade portion 4b of the moving knife. 4. FIG. 4 is a timing chart showing the relationship among the needle bar down detection, the thread tension regulator, the thread cutting operation and the like.

[0026]

As described above, the thread cutting device for a sewing machine according to the present invention includes the thread tension releasing means for bringing the thread tension regulator into the released state after properly capturing the sewing thread to be cut by the driving knife of the cutting means. Since it is driven, it is possible to eliminate the inconvenience of cutting the needle thread on the sewing needle side, which must not be cut.

[Brief description of drawings]

FIG. 1 is a block diagram showing a state in which a thread cutting device of a sewing machine according to the present invention is installed on a sewing machine.

FIG. 2 is a perspective view showing a configuration state of thread tension releasing means of the thread cutting device of the sewing machine according to the present invention.

FIG. 3 is an explanatory view showing a state in which the moving knife of the thread cutting device of the sewing machine according to the present invention properly captures the sewing thread to be cut.

FIG. 4 is a timing chart showing the operation of the thread tension regulator or the like according to the present invention and the operation of the conventional thread tension regulator.

FIG. 5 is an explanatory view showing a position state of the sewing thread below the article to be sewn at the end of sewing of the sewing machine.

FIG. 6 is an explanatory diagram showing a state in which a moving knife of a conventional thread cutting device captures three threads of two upper threads and a lower thread to cause thread cutting failure.

FIG. 7 is an explanatory diagram showing a cut state of a sewing thread at the end of normal stitch formation.

FIG. 8 is an explanatory view showing a state of a sewing thread below a material to be sewn when a reverse feed small pitch stitch is formed.

[Explanation of symbols]

 4 Moving knife 5 Fixed knife 6 Cutting means 7 Thread tension releasing means

Claims (1)

[Claims] 1. A thread tension releasing means, which is provided between a balance of the sewing machine and a supply source of the sewing thread on the needle side and which releases a thread tension device that applies thread tension to the sewing thread, is located below the needle plate. A sewing machine including a fixed knife and a moving knife that captures a sewing thread between the rotary hook and the workpiece and moves toward the fixed knife, and cuts the sewing thread in cooperation with the fixed knife. In the thread cutting device, the thread tension releasing means is configured not to be driven until the moving knife captures the sewing thread, and the thread cutting apparatus of the sewing machine.