JPS6038469Y2 - Variable pressure pretension device for sewing machine - Google Patents

Description

[Detailed description of the invention] The present invention relates to an upper thread unwinding device for a sewing machine, and in particular, the upper thread unwinding device is designed to prevent fluctuations in the tension of the upper thread due to inertia when the upper thread of the sewing machine is unwound from a thread spool. The invention relates to a device equipped with a variable pressure retention device.

As is well known, the needle thread pay-out device of a sewing machine is designed to reduce the tension of the needle thread during sewing, in order to eliminate variations in thread tension due to inertia when thread is fed out from the thread spool, and is effective when sewing thin fabrics. It is required that there be.

Conventionally, a certain amount of needle thread that is let out by a needle thread unwinding device of a sewing machine is simply left slack between the thread spool and the tension plate of the dial tension.

Therefore, if the pressure on the tension plate is weak, the resistance due to the inertia of the thread spool will be greater than the pressure on the tension plate, causing the upper thread to move backwards during unwinding, preventing a certain amount of thread from being paid out from the thread spool, resulting in variations in thread tension, and making it impossible to stitch neatly. This was a drawback.

In order to eliminate the above-mentioned drawbacks, the present invention has a variable pressure pre-tensioning device installed in the upper thread path between the thread spool and the dial tension of the sewing machine, and the feeding arm provided on the device is placed above the thread spool. The tension is set so that the tension is high when the thread is paid out, and the tension is 1 to 2 gw at other times, and the timing between the balance and the feeding arm of the device is set so that the thread is not near the top dead center. It is an object of the present invention to provide a device for supplying a fixed amount of upper thread in such a way that the reeling-out arm unwinds the upper thread when the upper thread is positioned at a position, thereby preventing the upper thread from moving backward.

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a front view of essential parts of an embodiment of the present invention, and FIG. 2 is a side view of the same.

In the figure, reference numeral 1 indicates a sewing machine frame 2, which is the main shaft, but only shows the main parts of the embodiment of the present invention, and other parts are omitted.

A main shaft 2 is rotatably mounted horizontally on a sewing machine frame 1, and a ring-shaped cam surface 4a is arranged in parallel with a counterbalance crank 3 fixed to the end of the main shaft 2 and fitted around the counterbalance crank 3. A cam 4 is attached.

Reference numeral 5 denotes a thread feeding arm whose one end 5a is pivoted to the sewing machine frame 1 with a shaft pin 6, and a spring 7 is stretched between it and the machine frame 1a so that the protrusion 5b abuts against the cam surface 4a. There is.

Further, above the thread letting-out arm 5, a tension pawl having a thread letting-out arm 8 and a spring presser 9a, which will be described later, is provided in a bifurcated shape.

The thread paying-out arm 8 is adapted to pay out the upper thread 20 by being caught in the rotation of the cam 4, which causes the thread paying-out arm 5 to swing against the spring 7.

The tension claw 9 having the spring presser 9a is connected to the thread payout arm 8.
As mentioned above, the tensioning shaft 12 is integrally fixed in a bifurcated manner above the thread unwinding arm 8 and protrudes inward from the tensioning frame 10 fixed to the machine frame 1 so as to operate in synchronization with the tensioning shaft 12. The spring holder 9a is inserted into the spring holder 9a.

Moreover, the britension plate 13 is attached to the britension shaft 12.
An elastic body 16 and a helical spring 14 are attached to constantly pressurize the britension plate 13 with a force of 1 to 2 gw, and these constitute a britension mechanism.

With the operation of the spring presser 9a, the helical spring 14 presses the tension plate 13 through the elastic body 16 and presses the tension plate 13 against the tension frame 10, so that the thread take-up 1 is pressed during sewing.
5 to prevent the upper thread 20 from being pulled out excessively from the thread spool 19, and when the upper thread 20 has been completely paid out, the upper thread 20 is pressed by the elastic body 16 against the tension plate with a pressure of 1 to 2 gW. Brittention is added.

Further, the dial tension 21 provided between the balance 15 and the pre-tension mechanism is well known, and the dial tension shaft 21 provided protruding from the tension frame 10
2, a tension plate 23, a tension spring 24, and an adjustment dial 25.

By rotating the adjustment dial 25, the tension applied to the needle thread 20 inserted between the tension frame 10 and the tension plate 23 is adjusted.

Therefore, when the thread take-up 15 is descending, the tensioning mechanism is activated by the helical spring 14 to raise the upper thread 20.
At the same time, the thread pay-out arm 8 pays out the needle thread 20, and the amount of the feed-out is the amount of the needle thread 20 used at the maximum feed width, maximum swing width, and maximum possible fabric thickness. The needle thread 20 corresponding to the next stitch is prepared between the thread spool 19 and the thread spool 19.

Next, when the thread take-up 15 is raised and the thread is tightened, the thread pay-out arm 8 is in a position where it does not come into contact with the upper thread 20, and the tensioning mechanism is applied with a pressure of 1 to 2 gw by the elastic body 16. is added to the needle thread 20, and the needle thread 20 that has been previously paid out and prepared is supplied to the thread take-up 15.

FIG. 3 is a diagram showing the timing of the thread take-up 15 and the thread pay-out arm 8.

As shown in the figure, thread tightening by the thread take-up lever 15 during sewing is performed just before the needle reaches the top dead center (rotation angle of the main shaft 2 is 30° to 4°).
0°) to the top dead center (rotation angle of the main shaft 2 from 60° to 70°), but in order to easily thread the upper thread 20 into the thread path, the machine is stopped by the top dead center button. Taking into account the position (main shaft 30° to 40°), a range with a margin before and after the range C of the rotation angle of the child shaft 2 where the thread tightening is performed is defined as an immovable range d in which the thread payout arm 8 does not operate. .

When the rotation angle of the main shaft 2 is outside the fixed range d, the thread letting-out arm 8 is activated.The maximum timing for letting out the thread letting-out arm 8 is approximately in the middle of the operating range of the thread letting-out arm 8.

As explained in detail above, the present invention provides an upper thread pay-out arm and a pre-tension mechanism between the known dial tension and the thread spool, thereby preventing the thread from moving backwards and preventing the thread from moving backwards from the thread spool. It has the effect of making it possible to stably supply a certain amount of needle thread, and making it possible to maintain uniform thread tension and obtain clean stitches.

[Brief explanation of the drawing]

FIG. 1 is a front view of essential parts of an embodiment of the present invention, FIG. 2 is a side view of the same, and FIG. 3 is a diagram showing the timing of the thread take-up arm and the thread pay-out arm. 4: Cam, 5: Thread payout arm, 7: Spring, 8: Thread payout arm, 9: Tension claw, 9a: Spring holder, 10: Tension frame, 12 Nib tension shaft, 13 Nib tension plate, 14: Hanging spring, 15: Balance, 16
: Elastic body, a: Vertical displacement of the thread take-up, b: Movement of the thread payout arm, C: Range where thread tightening is performed, d: Fixed range.

Claims (1)

[Scope of utility model registration request] In the thread path of the upper thread between the thread spool and the dial tension of the sewing machine, a britension shaft protruding inward is provided on the tension frame, and the britension shaft is connected between the tension frame and the tension frame. The britension mechanism is such that a spring holder inserted into the cam presses the britension plate with a helical spring through an elastic body, and a spring is attached to the cam surface of a cam that rotates in synchronization with a counterbalancing crank that is linked to the main shaft. The tension pawl is integrally formed with the spring presser of the pre-tensioning mechanism, and is provided on the sewing machine frame so as to abut and swing when biased, and the thread pay-out arm body is provided with a thread pay-out arm on the upper part. The thread is not let out near the top dead center of the take-up, but the thread is let out at other points. On the other hand, the pre-tension mechanism applies pre-tension to the upper thread between the tension frame and the pre-tension plate. A variable pressure retension device for a sewing machine, characterized in that it prevents reverse movement when feeding out.