JPS6047871B2 - automatic thread cutter sewing machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an automatic thread-cutting sewing machine equipped with a thread-cutting mechanism.

PRIOR ART In this type of conventional automatic thread trimming sewing machine, a thread trimming signal is generated based on a thread trimming signal generated while the needle moves from a lower position to an upper position in synchronization with the lifting of the thread take-up body of the thread take-up mechanism at the end of a sewing operation. Then, the thread cutting mechanism is activated, and necessary threads such as upper and lower threads connected to the work cloth are captured, let out, and then cut.

However, in this conventional sewing machine, there is a large variation in the length of the needle thread remaining on the needle side after the thread is cut by the thread trimming mechanism. If the upper thread comes out of the needle and it becomes impossible to continue sewing, or if the remaining length of the upper thread is long, the amount of thread remaining on the underside of the workpiece fabric will increase when sewing the next time.
This resulted in a decrease in the quality of the processed product, and sometimes it was necessary to manually cut and remove the thread ends connected to the processed fabric.

When we investigated the cause of large variations in the remaining length of upper thread in this conventional automatic thread trimming sewing machine, we found the following facts. In other words, with this type of sewing machine,
There is usually an auxiliary thread tension device on the needle thread path from the needle thread supply source to the needle.
A main thread tension device, a thread take-up spring, and a thread take-up mechanism are arranged in this order, and during sewing operation, when the needle thread is supplied to the thread loop catcher by lowering the thread take-up body in relation to the thread take-up mechanism, the thread take-up spring is The thread take-up spring is moved to the first position to absorb the slack of the upper thread, and at the end of the operation of picking up the upper thread from the thread ring catcher by raising the thread take-up body, the thread take-up spring is moved to the second position and becomes the upper thread supply source. Above. It is designed to allow the thread to be let out.

However, in automatic thread trimming sewing machines, when the thread trimming mechanism operates and the required thread is caught, fed out, and then cut, the thread tension pressure from the main thread tension device is released and the upper thread is cut. Let's roll out! It is becoming easier to do. Therefore, when the thread tension pressure of the auxiliary thread tension device is set to be weaker than the spring force for returning the thread take-up spring to the first position, when the thread is fed out and cut by the thread trimming mechanism, the thread take-up body As the thread tension rises, the thread take-up spring should normally be moved to the second position as described above, but the needle thread is easily supplied from the needle thread supply source through the sub-thread tension device. Therefore, the thread take-up spring is not placed in the second position, but is moved back toward the first position by its own return spring force. The amount of return movement of the thread take-up spring when cutting the thread varies slightly depending on the type and thickness of the work cloth used for sewing, the type and thickness of the thread, the operating speed of the previous thread trimming mechanism, etc. Therefore, the length of the upper thread remaining on the needle side after the thread is cut varies greatly, and the length of the upper thread remaining on the needle thread becomes the longest when the thread take-up spring is completely returned to the first position. Further, if the thread tension pressure of the auxiliary thread tension device is set to be stronger than the return spring force of the thread take-up spring, the upper thread is supplied from the upper thread supply source through the auxiliary thread tension device when the thread trimming mechanism is activated. Since the thread is not easily supplied, the thread take-up spring is moved to the second position until the required thread is let out and cut by the thread cutting mechanism.

However, when the thread cutting mechanism finishes cutting the thread,
Since the tension of the needle thread extending from the thread take-up spring toward the needle side is released, the thread take-up spring is moved back from the second position to the first position, and the needle thread extending toward the needle side is pulled up and the above-mentioned "needle thread" The remaining amount is minimized.This invention was made in order to eliminate the above-mentioned defects in conventional sewing machines, and its purpose is to reduce the action of the thread take-up spring at least while the thread trimming mechanism is operated. To provide a new automatic thread trimming sewing machine in which the amount of needle thread fed out by a thread trimming mechanism is always constant and the length of needle thread remaining on the needle side after thread cutting can be kept constant by disabling the thread trimming mechanism. It is in.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. A frame 1 of a sewing machine is composed of an arm 2 and a bed (not shown), and a main shaft (not shown) is installed in the arm 2.
is rotatably supported.

A needle bar 4 having a needle 3 at its lower end is supported so as to be movable up and down, and a presser bar 5 having a presser foot (not shown) at its lower end is supported so as to be movable up and down. Second
As shown in the figure, a well-known fully rotary thread ring catcher 6 is provided in the bed, and is composed of an outer hook 6b having a tip 6a and an inner hook 6c whose rotation is restrained by an inner hook stopper 7. When the bobbin case 8 containing the bobbin (not shown) is attached, it is rotated at twice the speed of the main shaft in conjunction with the rotation of the main shaft, and in cooperation with the needle 3, the workpiece cloth is On the other hand, it is designed to form a lock stitch. As shown in FIG. 2, a fixed blade 9 of a thread cutting mechanism is disposed in the bed near one side of the thread ring catcher 6.

A movable blade 10 of a thread cutting mechanism is rotatably disposed near the other side of the thread ring catcher 6 so as to correspond to the fixed blade 9, and has a thread handling section 10a and a thread catching recess 10b at its tip. and a blade portion 10c are formed. At the end of the sewing operation, the movable blade 10 is rotated clockwise in FIG. 2 based on a thread cutting signal generated while the needle 3 moves from the lower position to the upper position, and the upper thread T1 is threaded. By catching the timing when the ring comes off the tip 6a of the outer hook 6b and being picked up,
The upper thread T1 and the lower thread T2 connected to the work cloth are simultaneously captured and fed out, and then cut in cooperation with the fixed blade 9. A thread take-up mechanism is provided in the arm 2 and is operated as the main shaft rotates, and as shown in FIG.
The upper thread T1 protrudes onto the path of the upper thread T1 guided to the needle 3 through a plurality of thread guide bodies 12, and the upper thread T1 is inserted into the thread hole 11a.
It is now possible to insert the

Then, as the thread take-up body 11 descends, the upper thread T1 is supplied to the thread ring catcher 6, and as the thread take-up member 11 ascends, the upper thread T1 captured by the thread ring catcher 6 is supplied. It is starting to be taken up. The balance body 11
A main thread tension device 13 is provided on the front surface of the arm 2 so as to be located on the needle thread path closer to the needle thread supply source.

Therefore, the structure of the main thread tension device 13 will be explained in detail with reference to FIGS. 3,
As shown in FIG. 4, a through hole 15a is formed on the outer periphery near the front end. A fixing screw 16 is attached to the thread tension table 15.
A cylindrical thread tension shaft 17 is fixed therethrough, and has a cut groove 17a and a threaded portion 17b formed at its front end, and a locking groove 17c formed on the outer circumferential surface of the central portion. A pair of thread tension discs 18 are rotatably inserted and supported at the front end of the thread tension shaft 17, and the upper thread T1 is passed between the thread tension discs 18.

A spring receiver 1 is attached to the thread tension shaft 17 in front of the thread tension disc 18.
9 is inserted and supported, and an engaging portion 19a formed at the center thereof.
By engaging with the cut groove 17a of the thread tension shaft 17, it is possible to move only in the axial direction of the thread tension shaft 17.
A thread tension spring 20 is inserted into the thread tension shaft 17 in front of the spring receiver 19, and a threaded portion 17b at the tip of the thread tension shaft 17 is inserted into the thread tension shaft 17.
A predetermined thread tension pressure is applied to the upper thread T1 between the two thread tension discs 18 via the spring receiver 19 based on the adjustment operation of the adjustment dial 21 screwed into the thread tension plate 18. A release pin 22 for releasing thread tension pressure is inserted and supported in the center of the thread tension shaft 17 so as to be movable in the axial direction, and the release pin 22 is configured to engage with the engaging portion 19a of the spring receiver 19 at its front end. It's summery. An operating pin 23 is supported within the arm 2 so as to be movable in the front-rear direction so as to extend on the same axis as the release pin 22 behind the release pin 22.
As shown in the figure, when the operating pin 23 is moved forward, the spring receiver 19 is moved forward via the release pin 22,
The spring pressure of the thread tension spring 20 on the thread tension plate 18 is released, and the thread tension pressure on the upper thread T1 is released. On the other hand, a sub-thread tension device 24 is provided on the upper surface of the arm 2 so as to be located on the needle thread path closer to the needle thread supply source than the main thread tension device 13 .

As shown in FIG. 1, the auxiliary thread tension device 24 consists of a pair of thread tension discs 25, a housing body 26 containing a thread tension spring (not shown), and an adjustment dial 27 for adjusting the thread tension pressure. , a predetermined thread tension pressure is applied to the upper thread T1 between the thread tension discs 25. or,
As shown in FIGS. 1, 3, 4, and 7, in the thread tension stand 15 of the main thread tension device 13, a thread take-up spring 28 is wound approximately at the center of the thread tension shaft 17, and one end of the thread take-up spring 28 is wound around the thread tension shaft 17. Tone axis 1
7 is latched and fixed in the latching groove 17c of 7, and the other end protrudes outward through the through hole 15a of the thread tension board 15.
A thread hooking portion 28a for hooking the needle thread T1 on the needle thread path closer to the needle 3 than the thread tension plate 18 of the main thread tension device 13 is bent at the other end.

The thread hooking portion 28a of the thread take-up spring 28 is always urged toward the first position shown by the chain line in FIG. When the upper thread is supplied to the thread ring catcher 6 due to the lowering of the needle thread T1, the thread hooking part 28a is moved to the first position to absorb the slack of the upper thread T1, and the upper thread is removed from the thread ring catcher 6 by the rise of the thread take-up body 11. At the end of the needle thread take-up operation, the first thread hooking section 28a is moved to the second position shown by the solid line in FIG. 4, allowing the needle thread T1 to be fed out from the needle thread supply source.
As shown in FIGS. 1, 3, 5, 6, and 7, the main thread tension device 1
A lock shaft 29 is rotatably supported between the front and rear walls of the arm 2 in the vicinity of the arm 3 .

A rotating plate 31 is fixed to the front end of the lock shaft 29 by a mounting screw 30, and a bifurcated portion 31a is formed at the tip thereof. A lock plate 3 is rotatably supported on the thread tension shaft 17 between the thread tension plate 18 of the main thread tension device 13 and the thread take-up spring 28, and the two-pronged portion of the rotation plate 31 is attached to the tip of the lock plate 3. An engagement pin 32a that engages with the thread take-up spring 28 is provided in a protruding manner, and an engagement piece 32b that engages near the thread hooking portion 28a of the thread take-up spring 28 is bent on the outer periphery of the base end. Normally, the rotating plate 31 and the locking plate 32 are arranged in the state shown in FIG. When the lock shaft 29 is moved freely and rotated clockwise in FIG.
2 is rotated counterclockwise, as shown in Figures 4 and 5. The thread take-up spring 28 is held by the engaging piece 32b of the lock plate 32.
The threading portion 28a is held immovably in the second position so that its action is nullified. Next, the thread cutting mechanism consisting of the movable blade 10, etc. A configuration for releasing the thread tension pressure by the main thread tension device 13 will be described so that the upper thread T1 can be easily paid out during operation.

Now, as shown in FIGS. 7 to 9, the arm 2
A rotation shaft 33 is rotatably supported through the rear wall of the housing. A release lever 34 is fixed to the inner end of the rotation shaft 33 at its end by a fixing screw 35, and a Bowden cable 36 extending from the thread cutting mechanism is connected to the tip thereof. 4. Then, when the thread trimming mechanism is activated based on the thread trimming signal generated at the end of the sewing operation of the sewing machine, the release lever 34 is rotated clockwise via the Bowden cable 36 to the state shown in FIG. and is adapted to be held in that position during operation of the thread trimming mechanism. A two-arm lever 37 for pushing up is rotatably supported on a rotating shaft 33 behind the release lever 34, and a push-up lever 37 provided on the sewing machine table is attached to the tip of one arm 38. A connecting rod 40 extending from a knee pedal (not shown) is connected, and the other arm 39 has an engaging surface 39a and a cam surface 3.
9b is formed.

An operation shaft 41 is rotatably supported through the rear wall of the arm 2 in the vicinity of the rotation shaft 33, and a manual push-up lever 42 is attached to the outer end of the operating shaft 41. A cam body 43 that engages with the engagement surface 39a of the arm lever 37 is fixed. When the two-arm lever 37 is rotated clockwise from the state shown in FIG. 8 through the link 40 by operating the knee pedal, or by operating the manual push lever 42, When the two-arm lever 37 is rotated clockwise via the body 43, the cam surface 39b on the other arm 39 and the arm lever 4 provided on the presser bar 5
4, the presser bar 5 and the presser foot at its lower end are lifted up. A cam lever 45 is rotatably supported on the rotation shaft 33 between the release lever 34 and the two-arm lever 37, and the operating pin is mounted on one front side of the cam lever 45 as shown in FIGS. A high cam surface 45a1 that engages with the rear end of 23, an inclined surface 45b, and a low cam surface 45c.
is formed, and a linking pin 45d that can be engaged with the release lever 34 and the two-arm lever 37 is provided protruding from the front and rear surfaces of the other side.

A coiled spring 46 is wound around a boss portion on the inner surface of the arm 2 that supports the rotating shaft 33, and one end of the coil spring 46 is hooked to the cam lever 45, and the other end is attached to a latching protrusion 47 on the inner surface of the arm 2.
The cam lever 45 is rotated counterclockwise in FIG. 8. Therefore, normally, the cam lever 45 is held at its original position where its lower cam surface 45c engages with the actuating pin 23 by the action of the coiled spring 46, and the main thread tension device 13 is in tension with respect to the upper thread T1. It is placed in a state where it applies a tone pressure.

When the release lever 34 is rotated clockwise to the state shown in FIG. 8 in conjunction with the operation of the thread trimming mechanism as described above, or by operating the knee pedal for push-up or the manual push-up lever 42, the arm is released. When the lever 37 is rotated clockwise, the cam lever 45 is rotated clockwise from the original position via the linking pin 45d, and the operating pin 23 is moved to the high cam of the cam lever 45 as shown in FIGS. Surface 45a
Before engaging with. 2, and the main thread tension device 13 is switched to the state where the thread tension pressure is released via the release pin 22.
Next, a description will be given of a configuration for rotating the lock shaft 29 and holding the thread take-up spring 28 at the second position by the lock plate 32 when the thread trimming mechanism is activated. Now, number 7,
As shown in FIGS. 9, 10, 11, 12, and 13, a rotating arm 48 is fixed at its base end to the rear end of the rotating shaft 33 on the rear surface of the arm 2, and is integrally connected to the rotating shaft 33. It is designed to be rotated.

Further, an actuating body 49 is fixed at the proximal end to the rear of the lock shaft 29, and a connecting pin 49a is protruded from the rear surface of the distal end thereof, and a locking protrusion 49b is formed at the distal end. . A tension spring 51 is hung between the actuating body 49 and a latch pin 50 on the arm 2, and urges the actuating body 49 to rotate clockwise in FIG. 9. A connecting plate 52 is attached at one end to the tip of the rotating arm 48 by a pin 53, and an elongated hole 52a into which a connecting pin 49a of the operating body 49 fits is formed at the other end. A support plate 55 is attached to the rear surface of the arm 2 above the operating body 49 with attachment screws 54 .

A two-pronged locking claw 57 is rotatably supported on the rear surface of the lower end of the support plate 55 by a stepped screw 56, and one arm of the two-pronged locking claw 57 engages with the locking protrusion 49b of the operating body 49. A claw portion 57a is formed on the other arm, and an actuating piece 57b is bent on the other arm. A coil spring 58 is wound around the stepped screw 56, and both ends of the spring 58 are hooked to a locking pawl 57 and a support plate 55, respectively, to urge the locking pawl 57 to rotate clockwise in FIG. I'm starting to do that. and,
During normal sewing operation, the rotating arm 48 and the operating body 49 are in the state shown in FIG. 13, and the rotary plate 31 and lock plate 32 on the front surface of the arm 2 are held in the state shown in FIG. Movement of the thread take-up spring 28 is allowed.

When the thread trimming mechanism is activated based on the thread trimming signal generated at the end of this sewing operation and the release lever 34 is rotated clockwise together with the rotation shaft 33 to the state shown in FIG. 8, the arm 2 The rear rotating arm 48 is rotated counterclockwise from the state shown in FIG.
As shown in FIG. 1, the actuating body 49 is held in its rotational state by engagement between its locking protrusion 49b and the claw portion 57a of the locking claw 57. As a result, the lock plate 32 on the front surface of the arm 2 is rotated counterclockwise from the state shown in FIG. 6 via the rotation plate 31, and as shown in FIGS. At this time, the thread hooking portion 28a of the thread take-up spring 28 is held immovably in the second position, and its action is nullified. When the thread cutting operation of the thread cutting mechanism is completed and the release lever 34 is rotated back from the state shown in FIG. 8 in the counterclockwise direction together with the rotation shaft 33, the rotation arm 48 is
It is rotated clockwise from the state shown in FIG. 1, and only the connecting plate 52 is moved back as shown in FIG. Also, the 7th, 9th,
As shown in Figures 11, 12, and 13, a solenoid 59 is attached to the support plate 55 on the rear surface of the arm 2.
The armature 59a is the operating piece 57b of the locking pawl 57.
It is becoming more and more engaged.

At the start of the next sewing operation, the solenoid 59 is temporarily energized based on a lock release signal generated after the second and third needles 3 penetrate the workpiece cloth. Therefore, in the state shown in Fig. 12, the solenoid 5
9 is excited and its armature 59a is projected,
The locking pawl 57 is rotated counterclockwise against the action of the coil spring 58, and its pawl portion 57a engages with the locking protrusion 49 of the actuating body 49.
b, and the actuating body 49 is rotated together with the lock shaft 29 to return to the position shown in FIG. 13 by the action of the tension spring 51. As a result, the rotating plate 31 and the locking plate 32 on the front surface of the arm 2 are rotated back from the state shown in FIG. 57 to the state shown in FIG. 6, and the thread take-up spring 28 is released from the locked state. Next, the operation of the sewing machine constructed as described above will be explained according to the flowchart of FIG. 14.

9 Now, during sewing operation by pressing the front of the operating pedal (not shown), etc., the rotating arm 48, actuating body 49, etc. on the rear surface of the arm 2 are arranged in the state shown in FIG. The rotating plate 31 and the locking plate 32 are arranged in the state shown in FIG. 6, and the thread take-up spring 28 is in a state where it can be moved between the first position shown by the chain line and the second position shown by the solid line in FIG. .

Therefore, in this state, when the main shaft (not shown) rotates, the needle 3 and the thread take-up body 11 are moved up and down, and the thread ring catcher 6 is rotated, so that the needle 3 and the thread ring catcher 6 cooperate with each other. As the thread take-up spring 28 descends, the thread take-up spring 28 moves from the second position to the first position due to its own spring force. The slack of the upper thread T1 is absorbed, and as the thread take-up spring 11 rises thereafter, the thread hooking portion 28a of the thread take-up spring 28 is moved from the first position to the second position against its own spring force. At the same time, the insufficient needle thread amount for one pitch corresponding to the feed amount of the work cloth is paid out from the needle thread supply source. Therefore, stitches with good thread closure are formed on the work cloth. When the forward depression of the operation pedal is released at the end of the sewing operation on the workpiece cloth, the main shaft is stopped at a rotation angle of 180 degrees, and the needle 3 is stopped at the downward position, as shown in FIG. be done.

Thereafter, when the operation pedal is pressed backward, the main shaft is rotated at a low speed, and the needle 3 is slowly raised from the lower position to the upper position. When the rotation angle of the main shaft reaches 230 degrees, the hand 3 rotates at a low speed. A thread trimming signal is generated by a position detection device or the like. Therefore, based on the thread trimming signal, the movable blade 10 of the thread trimming mechanism shown in FIG. 2 was rotated clockwise, and the upper thread T1 and lower thread T2 connected to the work cloth were caught and let out at the same time. later cut off. On the other hand, when the thread trimming mechanism starts operating, the release lever 34 is rotated clockwise together with the rotation shaft 33 via the Bowden cable 36, and the cam lever 45 is rotated in the same direction via the linking pin 45d, as shown in FIG. The high cam surface 45a is rotated so that the operating pin 2
3.

As a result, as shown in FIG. 3, the operating pin 23, the release pin 22, and the spring receiver 19 are moved forward, and the tension pressure on the upper thread T1 by the main thread tension device 13 is released. Therefore, during the cutting operation of the thread trimming mechanism, the upper thread T1 is easily paid out via the main thread tension device 13 in the pressure release state 4. Also, as the rotation shaft 33 rotates, the first
The operating body 49 in the state shown in FIG.
2 in the counterclockwise direction together with the lock shaft 29, and as shown in FIG. As a result, the lock plate 32 on the front surface of the arm 2 is rotated from the state shown in FIG. 6 to the state shown in FIG. and its effect is nullified. Therefore, when the upper thread T1 is paid out in accordance with the operation of the thread trimming mechanism, the rotating speed of the movable blade 10, the set thread tension pressure of the sub thread tension device 24 on the arm 2, the type and thickness of the work cloth, etc.
The thread take-up spring 28 is not moved between the first position and the second position due to the influence of the type and thickness of the thread, and the amount of needle thread fed out by the thread trimming mechanism is always constant. hand,
The length of the upper thread T1 remaining on the side of the needle 3 after the thread is cut can be kept constant. Therefore, if the remaining length of the upper thread is set appropriately, the remaining length of the upper thread will be too short and the upper thread will come off from the needle 3 when the next sewing starts, making it impossible to continue sewing. Or, there is no possibility that the remaining length of the needle thread is too long and the amount of remaining thread end connected to the lower surface of the workpiece fabric becomes large during the next sewing, resulting in deterioration of the quality of the workpiece.
Then, when the thread cutting mechanism finishes cutting the upper and lower threads Tl and T2 and the main shaft reaches a rotation angle of 60 degrees as shown in FIG. 14, its rotation is stopped and the needle 3 reaches the top dead center. The balance body 11 is stopped at an upper position slightly lower than the top dead center, and the balance body 11 is stopped at an upper position slightly before the top dead center.

Further, when the sewing machine is stopped, the thread trimming signal is also erased, and the operation of the thread trimming mechanism is stopped based on the signal. As a result, the release lever 34 is rotated counterclockwise together with the rotation shaft 33 from the state shown in FIG. 8, and the main thread tension device 13 is returned to the state in which thread tension pressure is applied to the upper thread T1. However, with the rotation of the rotation shaft 33, only the rotation arm 48 and the connecting plate 52 on the rear surface of the arm 2 return from the state shown in FIG. 11 to the state shown in FIG. Since the rotation plate 31 and lock plate 32 on the front surface of the arm 2 are not rotated from the state shown in FIG. 5, the thread take-up spring 28 is held in the second position. It is in the same condition as it was. In this state, when the next sewing operation is started by pressing the operation pedal forward, the needle 3 is lowered from the upper stop position as the main shaft rotates, and the thread take-up body 11 is lowered through the top dead center. As described above, a lock stitch is formed on the workpiece cloth by the cooperation of the needle 3 and the thread loop catcher 6.

At the start of this sewing, the thread take-up spring 28! If it is not held in the second position, its thread take-up spring 28
is moved back to the first position by its own spring force, and in a state where the needle thread amount for 3 to 5 pitches corresponding to the feed amount of the work cloth is held in the threading portion 28a, the needle thread for the first stitch is moved. Since the needle 3 begins to descend from the upper stop position 1, the thread take-up spring 28 remains in the first position even when the thread take-up body 11 is lowered, and the slack in the needle thread T1 is not absorbed. After that, when the thread take-up body 11 is raised, one amount of upper thread corresponding to one pitch corresponding to the feed amount of the work cloth is let out from above the thread take-up spring 28, and the thread take-up spring 28 is moved from the first position by that amount of thread. is moved to the second position.

Then, from the second stitch onwards, by repeating this operation, the amount of needle thread held in the thread take-up spring 28 is sequentially consumed as the thread take-up body 11 rises; When the thread take-up spring 28 is raised, the thread take-up spring 28 is moved to the second position, and thereafter, as described above, the thread take-up spring 28 is moved to the second position.
As the thread take-up spring 28 is raised and lowered, the thread take-up spring 28 is alternately moved between the second position and the first position. Therefore, as shown in FIG. 154, the stitches S formed on the workpiece cloth C from the start of sewing to the 3rd to 5th stitches had very poor thread binding. However, in the sewing machine of this embodiment, since the thread take-up spring 28 is immovably held in the second position by the lock plate 32 etc. as shown in FIG. The thread take-up spring 28 is not moved as the thread take-up body 11 moves up and down until the stitch is formed.
1, the thread loop of the needle thread T1 is reliably picked up from the thread loop catcher 6, thread tightening is performed, and a beautiful stitch with a good thread end is formed.

Then, at the start of this sewing operation, when the second and third needles 3 reach the bottom dead center, the thread trimming signal at the end of the previous sewing operation is erased, and the next sewing operation is started. Therefore, under the condition that the operating pedal is depressed forward, a lock release signal is generated as shown in FIG. 14, and the solenoid 59 on the rear surface of the arm 2 is energized and its armature 59a is projected. As a result, the locking pawl 57 in the state shown in FIG. It is rotated clockwise to the state shown in FIG. 13. Therefore, the actuation plate 31 and the lock plate 32 on the front surface of the arm 2 are rotated from the state shown in FIG. 5 to the state shown in FIG. As you ascend and descend, the second
and the first position. Note that the present invention is not limited to the configuration of the embodiment described above, but can also be configured as follows.

(1) The thread take-up spring 28 is different from the first embodiment.
or an appropriate position between the first position and the second position.

(2) The action of the thread take-up spring 28 is configured to be nullified only while the thread trimming mechanism is in operation.

With this configuration, when the thread take-up spring 28 is released from its holding state while the upper and lower threads Tl and T2 are cut, the thread take-up spring 28 moves from the second position to the first position by its own spring force.
Since the needle thread T1 extending toward the needle 3 side is pulled up when the needle thread returns to the position shown in FIG.

(3) The holding of the thread take-up spring 28 is configured to be released immediately after the first needle 3 penetrates the work cloth at the start of the next sewing.

Note that, as in the above embodiment, the second to third
If the configuration is such that the holding of the thread take-up spring 28 is released after the needle 3 of the first stitch passes through the work cloth, the thread end of the needle thread T1 passed from the upper surface to the lower surface of the work cloth by the needle 3 of the first stitch is When the presser foot is moved downward, the hold on the thread take-up spring 28 is released, so while pulling up the end of the thread, the thread take-up spring 2
There is no possibility that 8 will be moved back from the second position to the first position by its own spring force.

(4) This invention is embodied in a sewing machine in which the thread take-up spring 28 is provided at a different position from the thread tension device 13 and on the needle thread path on the needle 3 side of the thread tension device 13.

(5) In addition, the configuration of each part may be arbitrarily changed without departing from the spirit of this invention.

Effects As detailed above, the present invention is configured so that the action of the thread take-up spring is nullified at least while the thread trimming mechanism is in operation, so that the amount of needle thread fed out by the thread trimming mechanism is always constant. This provides an excellent effect of keeping the length of the needle thread remaining on the needle side constant after the thread is cut.

[Brief explanation of the drawing]

Fig. 1 is a partial front view of a sewing machine embodying the present invention, Fig. 2 is a perspective view of the main parts of the thread loop catcher, Fig. 3 is a partially enlarged sectional view taken along line 3-3 in Fig. 1, Figure 4 is 4 in Figure 3.
5 is a partial sectional view taken along line 5-5 of FIG. 3, FIG. 6 is a partial sectional view showing the operating state of FIG. 5, and FIG. 8 is a partial sectional view taken along line 8-8 of FIG. 7, FIG. 9 is a partial rear view of the sewing machine, and FIG. 10 is a portion taken along line 10-10 of FIG. 9. Enlarged cross-sectional view, Figure 11 is the 1st
12 and 13 are partial sectional views showing the operating state of FIG. 11,
FIG. 14 is a flowchart showing the operation of this sewing machine, and FIG. 15 is a partial cross-sectional view of a work cloth showing the state of seam formation at the start of sewing in a conventional sewing machine. Sewing machine frame 1, arm 2, needle 3, thread loop catcher 6,
Fixed blade 9, movable blade 10 (these 9, 10, etc. constitute a thread trimming mechanism), the thread take-up body 11 (these 11, etc. constitute a thread take-up mechanism), main thread tension device 13, release pin 22 , operating pin 23, thread take-up spring 28, lock shaft 29
, a rotating plate 31, a lock plate 32 (these 29, 31, 32, etc. constitute a disabling means), a cam lever 45
(These 22, 23, 45, etc. constitute a thread tension pressure release means).

Claims (1)

[Claims] 1. A needle 3 vertically supported on an arm 2 of a sewing machine;
In order to form a lockstitch stitch by cooperation with the needle 3, a thread loop catcher 6 provided on the bed of the sewing machine and the thread loop caught by the thread loop catcher 6 are taken up. A thread take-up mechanism 11 etc. provided on the arm 2, a thread tension device 13 attached to the arm 2 so as to be located on the needle thread path closer to the needle thread supply source than the thread take-up mechanism 11 etc. Thread tension pressure release means 22, 23, 45, etc. for releasing the thread tension pressure caused by the tension device 13, and the thread tension device 13.
The thread take-up mechanism 1 is arranged on the upper thread path on the needle 3 side than the
In relation to the first position, there is a first position that absorbs the slack of the needle thread during the needle thread supply operation of the thread take-up mechanism 11, etc. a thread take-up spring 2 which is movable between a second position where the upper thread is let out and which is normally biased toward the first position;
8, which is provided close to the thread loop catcher 6, and which is provided close to the thread loop catcher 6, and
Thread trimming mechanism 1 for catching the required thread, feeding it out, and cutting it based on the thread cutting signal generated in synchronization with the vertical movement of the
0, etc., and the thread tension pressure release means 22, 23, 45, etc. are activated when the thread trimming mechanism 10, etc. is activated, the thread take-up spring 28
Nullifying means 29, 31, 32 for nullifying the effect of
An automatic thread trimming sewing machine characterized in that the disabling means 29, 31, 32, etc. are operated at least while the thread trimming mechanism 10 etc. are operated. 2. The automatic thread trimming sewing machine according to claim 1, wherein the nullifying means 29, 31, 32, etc. are configured to hold the thread take-up spring 28 at a second position. 3. The second aspect of the present invention is characterized in that the operation of the nullifying means 29, 31, 32, etc. is canceled after the first stitch 3 penetrates the work cloth at the start of the next sewing. The automatic thread trimming sewing machine described in section.