JPH026926Y2 - - Google Patents

Description

[Detailed description of the invention] This invention controls the tension of the upper thread to properly tighten the thread of the seam in a sewing machine that knots the upper and lower threads to form a final stitch in cooperation with the needle and hook. This invention relates to a needle thread control device for a sewing machine.

Conventionally, in lockstitch sewing machines such as those described above, a predetermined tension was applied to the upper thread using a thread tension device that presses the upper thread with a tension plate, but the main shaft of the sewing machine rotates once and stitches one stitch. For example, as shown in Figure 5, when the thread take-up rises to near the top dead center and the thread is tightened (A), when the needle penetrates the fabric and friction occurs between the fabric and the needle thread. (B), when the outer hook rotates to pull down the upper thread before the hook has finished handling the upper thread (C), when the upper thread is caught on the running foot just before it comes out of the hook (D) ), the needle thread tension increases momentarily. especially,
In the case of (C) and (D), the thread take-up is raised and the needle thread is paid out, so when the needle thread is further paid out due to this tension, the needle thread that has been paid out is sewn into the fabric by one rotation of the spindle. The length exceeds the preset length, resulting in insufficient thread tightening, which causes the stitches to become loose and deteriorate the quality of the sewn product.

The purpose of this invention is to eliminate the above-mentioned drawbacks of the conventional method by stopping the needle thread payout during the period from (C) to (D).

Hereinafter, an embodiment of this invention will be explained with reference to the drawings.A machine frame 2 is mounted on a table 1 and rotatably supports a main shaft (not shown) connected to a driving body (not shown) via a pulley 3. . A balance 4 connected to the main shaft via a known crank mechanism and a needle bar 5 having a needle 6 fixed to its lower end move up and down at the timing shown in FIG. Reference numeral 7 denotes a well-known thread tension device disposed on the upper thread path, which pinches the upper thread between tension discs to apply tension to the upper thread and to adjust the tension. Reference numeral 8 denotes a thread gripper placed on the needle thread path between the thread take-up lever and the thread tension device, and a pair of clamping plates 8a which are structured so that the needle thread is inserted between them, which are normally subjected to elastic force in directions that separate them from each other. , 8b and a solenoid SOL that presses the clamping plates 8a and 8b against elastic force by urging, and in conjunction with the biasing of the solenoid SOL, the clamping plates 8a and 8b press against each other and allow the threaded upper thread to be paid out. In response to the deenergization of the solenoid SOL, the clamping plates 8a and 8b release the pressure contact with the upper thread inserted at a distance due to their elastic force, allowing the upper thread to be let out. The pot (4th pot) placed below table 1
Figure) shows an inner hook 9 whose rotation is prevented by an inner hook stopper (not shown) that engages with an inner hook holder 9a, and a lower shaft (not shown) connected to the main shaft, which has a tip 10a and a runway holder 10b. This is a well-known device consisting of an outer hook 10 that rotates around an inner hook 9 in conjunction with each other.

The rotation angle detection means (Fig. 5) arranged between the main shaft and the machine frame 2 has a light emitter (light emitting diode) LD and a light receiver (phototransistor) ET arranged facing each other with a disc 11 fixed to the main shaft sandwiched between them. , the outer hook 1 is placed on the disk 11 immediately before the hook completes thread handling of the upper thread.
The light emitting diode LD and the photoreceptor FT are connected to each other during the period from when the tip 10a of the thread 0 is near the lowest point until the upper thread comes off the track presser 10b of the outer hook 10 and comes out of the hook.
Slit 11 in the rotation angle range of the main shaft located between
Provide a.

FIG. 3 shows an electric circuit related to this rotation angle detection means, in which a positive power source _E1 is connected to the anode terminal of the light emitting diode LD via a resistor R1, and the cathode terminal is grounded. The collector terminal of the phototransistor FT is connected to the positive power supply _E2 , and the emitter terminal is grounded through a resistor _R2 and connected to the base terminal of the transistor TR through an amplifier A.
A thread gripper 8 is attached to the collector terminal of the transistor TR.
The positive power supply _E2 is connected through the solenoid SOL and the flywheel diode D of the solenoid SOL, and the emitter terminal is grounded. That is, as shown in FIG. 3, the light from the light emitting diode LD passes through the slit 11a of the disk 11 and reaches the phototransistor.
When FT is reached, the phototransistor FT turns on, creating a voltage across the resistor _R2 , and current flows through the amplifier A to the base of the transistor TR, turning on the transistor TR and closing the solenoid SOL.
When the phototransistor FT is energized and the disk 11 moves and the light from the light emitting diode LD is blocked by the disk 11, the phototransistor FT is turned off.
TR is also turned off and solenoid SOL is deenergized.

This invention has the above structure, and its operation will be explained next.

Thread the upper thread using the thread tension device 7, thread gripper 8, thread take-up 4, and needle 6.
When the fabric W (Fig. 4) is placed on the table 1 and sewing is started, the thread take-up 4 continues to rise after the needle 6 reaches the top dead center as shown in Fig. 5. Since the solenoid SOL of the thread gripper 8 is deenergized, the upper thread S passes through the thread tension device 7 and is let out. When the thread take-up lever 4 reaches the top dead center, the thread is tightened, so that tension is applied to the upper thread S. occurs (Figure 5A).

Next, when the needle 6 penetrates the cloth W, the cloth W and the upper thread S
Friction occurs between the upper and lower threads and tension is generated on the upper thread S (Fig. 5B), but since the thread take-up lever 4 is descending at this time, the upper thread S is let out against the clamping force of the thread tension device 7. It won't happen. When the needle 6 rises slightly from the lowest point, the upper thread S is captured by the tip 10a of the outer hook 10 and drawn into the hook, so that so-called thread handling is performed. Just before the end of thread handling, as shown in Figure 4C, the length of the needle thread S drawn in by the hook reaches its maximum, so tension is generated in the needle thread S, but at this time, (Figure 5C), The optical path of the light emitting diode LD is opened by the slit 11a of the disk 11, and the phototransistor FT receives light and turns on, so the solenoid SOL is energized and the clamping plates 8a of the thread gripper 8,
8b comes into pressure contact, and the needle thread S is prevented from being fed out despite the rise of the thread take-up 5. When the thread handling is finished, the upper thread S leaves the tip 10a and is moved to the thread presser foot 10b.
, and rises as the outer hook 10 rotates.
(FIG. 4D) As the thread take-up lever 5 rises, the needle thread S is pulled upward and tension is generated in the needle thread S held by the running path presser 10b (FIG. 5D). SOL is still in the energized state, and the upper thread S is not let out. When the outer hook 10 further rotates in the direction of the arrow from FIG.
Since the light is blocked and the phototransistor FT is turned off, the solenoid SOL is deenergized and the upper thread S can pass through the thread gripper 8, and as the thread take-up lever 7 rises, the upper thread S is let out.

As described above, according to this invention, a thread gripper that can stop the feeding of the upper thread is provided, and the thread gripper is provided from just before the shuttle finishes handling the needle thread until the needle thread leaves the shuttle. During this time, even if needle thread tension as shown in FIG. Therefore, when the thread take-up reaches its highest point, the thread is sufficiently tightened, so that the stitches are aligned and the quality of the sewn product is improved.

The rotation angle detecting means of the main shaft is not limited to the light emitting body and slit shown in this embodiment, but may be composed of a magnet and a magnetically sensitive element, for example.

Further, in the above embodiment, the thread tension device and the thread gripping device are provided separately, but a single thread tension device can be configured to apply a constant tension to the upper thread or prevent the upper thread from being paid out. You can.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of the sewing machine, Fig. 2 is a sectional view of the thread gripper, Fig. 3 is an electric circuit diagram of the rotation angle detection means,
FIG. 4 is a diagram showing the relationship between the shuttle and the upper thread, and FIG. 5 is a diagram showing the relationship between the positions of the thread take-up and needle and the energizing timing of the solenoid of the thread gripper. The outer hook is 10, the balance is 4, the inner hook is 9, the thread gripper is 8, the rotation angle detection means are 11, 11a, LD, and the energizing circuit is FT, A, TR.

Claims (1)

[Claims for Utility Model Registration] A needle that moves up and down in conjunction with the main shaft and has an upper thread; a hook that rotates in conjunction with the main shaft and has a bobbin thread that captures the needle thread loop; and a thread take-up that moves up and down to pick up the needle thread loop captured by the hook, and a thread take-up that is installed on the needle thread winding side of the thread take-up to apply a clamping force to the needle thread and pull out the needle thread necessary to form one stitch when the thread take-up rises. In a sewing machine equipped with a thread tension device, the device is placed on the needle thread path between the needle thread supply source and the thread take-up thread, and is used to allow the needle thread to be fed out at all times, and to engage the needle thread by electrical energization. A thread gripper operable to stop the thread; a detection means arranged in relation to the spindle to detect a specific rotation angle range in one revolution of the spindle and generate a signal; and a thread gripper attached in relation to the signal of the detection means. The rotation angle range detected by the detection means is set to correspond to the period from when the tip of the outer hook is approximately at the lowest point until the needle thread comes out of the hook. Needle thread control device for sewing machines.