JPS6048196B2 - automatic thread cutter sewing machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an automatic thread trimming sewing machine equipped with a thread trimming 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, 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 thread trimming mechanism, etc., some thread remains on the needle side after the thread is cut by the thread trimming mechanism. If there is a large variation in the length of the upper thread and the remaining length of the upper thread is short, the upper thread will come off the needle when the next sewing starts, making it impossible to continue sewing, or the remaining length of the upper thread may be short. If the thread length is long, there will be a large amount of thread remaining on the underside of the pressurized fabric during the next sewing process, resulting in a decrease in the quality of the finished product, and sometimes the thread ends running on the fabric must be cut manually. It also needed to be removed.

OBJECT OF THE INVENTION The present invention has been made in order to eliminate the above-mentioned defects in conventional sewing machines, and its purpose is to release the thread tension pressure at least when the thread trimming mechanism is in operation, and to maintain the thread tension pressure in the released state. Immediately before the thread trimming operation, the required amount of thread is paid out in advance by the thread trimming mechanism, and an amount of thread smaller than the amount of thread that has been paid out is used within several stitches from the start of the thread take-up mechanism's first thread supply operation at the start of the next sewing. By pulling it up from the needle side, the amount of thread remaining at the beginning of the stitch can be optimized, and the thread can be prevented from falling out at the beginning of the sewing.
Moreover, it is an object of the present invention to provide an automatic thread trimming sewing machine that can improve the appearance of the sewing start portion.

EXAMPLE An example of the present invention will be described below with reference to the drawings.
Frame 1 of the sewing machine includes arm 2 and bed (not shown)
A main shaft (not shown) is rotatably supported within the arm 2.

A needle bar 4 having a needle 3 (shown in FIG. 4) at its lower end is supported on the head of the arm 2 so as to be movable up and down, and a presser bar 5 having a presser foot (not shown) at its lower end is movable up and down. Possibly supported. As shown in FIG. 4, a well-known fully rotary single thread catcher 6 is provided in the bed, and consists 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 a bobbin case 8 containing a bobbin (not shown) is installed, the spindle rotates at twice the speed relative to the spindle in conjunction with the rotation of the spindle. rotated,
In cooperation with the needle 3, a lock stitch is formed on the workpiece cloth. As shown in FIG.
A fixed blade 9 of a thread cutting mechanism is disposed in the bed near one side of the thread cutting mechanism 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.
At its tip, a thread handling section 10a1, a thread catching recess 10b and a blade section 10c are formed. At the end of the sewing operation, the movable blade 10 is rotated clockwise in FIG. 4 based on a thread trimming signal generated while the needle 3 moves from the lower position to the Hijikata position, and the upper thread T1 is The ring is the outer pot 6b
The upper thread T1 and the lower thread T2 connected to the work cloth are caught at the same time when they are removed from the tip 6a of the work cloth, and are fed out, after which they are cut in cooperation with the fixed blade 9. In this case, the thread payout amount is the minimum required so that the thread does not come out when starting the next sewing after thread cutting)
The amount is the yarn amount L plus the extra yarn amount 1. A balance mechanism that is operated as the main shaft rotates is provided in the arm 2, and as shown in FIGS. 1 to 3, the balance body 1
1 is a plurality of thread guide bodies 1 from an upper thread supply source (not shown).
The thread hole 11a protrudes onto the path of the upper thread T1 guided to the needle 3 through the thread hole 11a. 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. 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 than the thread take-up body 11 .

Therefore, to explain the structure of the main thread tension device 13 in detail, as shown in FIG.
A cylindrical thread tension stand 15 is fixed therethrough, and as shown in FIGS. 5 and 7, a through hole 15a is formed on the outer periphery near the front end of the thread tension stand 15. A thread tension shaft 17 is fixed through the thread tension stand 15 by a fixing screw 16, and a threaded portion 17 is provided at the front end of the thread tension shaft 17.
a is formed, and a locking groove 17b is formed on the outer periphery of the substantially 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 thread tension spring 19 is inserted into the thread tension shaft 17 in front of the thread tension disc 18, and both thread tension discs 18 A predetermined thread tension pressure is applied to the upper thread T1 between the threads. On the other hand, a sub-thread tension device 21 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 21 includes a pair of thread tension discs 22, a housing 23 containing a thread tension spring (not shown), and an adjustment dial 2 for adjusting thread tension pressure.
4, and a predetermined thread tension pressure is applied to the upper thread T1 between the thread tension discs 22. Further, as shown in FIGS. 5 and 7, in the thread tension stand 15 of the main thread tension device 13, a thread take-up spring 25 is wound approximately at the center of the thread tension shaft 17, and one end of the thread take-up spring 25 is wound around the thread tension shaft 17. 17, and the other end protrudes outward through the through hole 15a of the thread tension unit 15. A thread hooking portion 25a for hooking the needle thread T1 is formed by bending on the needle thread path on the needle 3 side.

The thread hooking portion 25a of the thread take-up spring 25 is always urged toward the first position shown by the solid line in FIG. When the upper thread is supplied to the thread ring catcher 6 by lowering, the thread hooking portion 25a is moved to the first position and the upper thread T is moved to the first position.
1, and at the end of the operation of picking up the needle thread from the thread loop catcher 6 due to the lifting of the thread take-up unit 11, the thread hooking portion 25a
is moved to a second position shown by a chain line in FIG. 7 to allow the needle thread T1 to be fed out from the needle thread supply source. As shown in FIGS. 5 and 8, the thread tension shaft 1 is located between the thread tension disc 18 of the main thread tension device 13 and the thread take-up spring 25.
A lock plate 26 is rotatably supported on the lock plate 7, and an engagement pin 26a is protruded from the tip thereof, and an engagement piece 26b facing the thread take-up spring 25 is bent on the outer periphery of the proximal end. has been done.

When the lock plate 26 is rotated to one position, as shown by the solid line in FIG. 1 and the two-dot chain line in FIG. The thread take-up spring 25 is allowed to move between the first position and the second position, and the locking plate 26 is rotated to the other position, as shown by solid lines in FIGS. 2 and 7. When this is done, the engaging piece 26b engages with the thread take-up spring 25 near the thread hooking portion 25a, and the thread take-up spring 25 is held immovably in the first position. As shown in FIGS. 1 to 3, a first solenoid 28 is attached to the front surface of the sewing machine arm 2 via a bracket 27, and its armature 28a protrudes when demagnetized and is retracted when energized.

In the vicinity of the first solenoid 28, a thread payout lever 30 that also serves as thread pull-up is supported by a stepped screw 29 on the front surface of the arm 2, and one arm portion 30a of the lever 30 is connected to the armature 28a via a connecting link 31. ing.
Further, this thread letting-out lever 30 is urged to rotate clockwise in FIG. 1 by a spring 32. And the first
As shown in the figure, when the first solenoid 28 is demagnetized, the biasing force of the spring 32 rotates the line pay-out lever 30 to a position where it is regulated by the stopper 33, and as shown in FIG. so that the first solenoid 2
8 is energized, the thread pay-out lever 30 is rotated counterclockwise and placed in a substantially horizontal state. The main thread tension device 13 is located at the tip of the other arm portion 30b of the thread letting-out lever 30.
A first auxiliary thread tension device 34 is provided between the first auxiliary thread tension device 21 and the first auxiliary thread tension device 21 . As shown in Figure 6, the first
The auxiliary thread tension device 34 includes a thread tension shaft 35, a pair of thread tension discs 36 fitted into the thread tension shaft 35, and a thread tension spring 3.
7 and an adjustment dial 38 for adjusting the thread tension pressure, and the upper thread T1 is held between the two tension discs 36. Then, the first solenoid 28 is energized and the thread pay-out lever 30 is rotated from the position shown in FIG. 1 to the position shown in FIG. The upper thread T1 that is present is let out from the upper thread supply source. This amount of let-out is approximately equal to the amount L+l of the upper thread T1 captured and let out by the movable blade 10 of the thread cutting mechanism. A thread letting-out means is constituted by the first solenoid 28, a thread letting-out lever 30 having a second auxiliary thread tension device 34, and the like. A release plate 39 is fixed to the upper part of the sewing machine arm 2, and the thread letting-out lever 3
0 is placed in the position shown in Fig. 1, this release plate 3
The tip insertion portion 39a of the thread tensioner 9 is inserted between the tension discs 36 of the first auxiliary thread tension device 34, and the thread clamping pressure is released. Below the first solenoid 28, a second solenoid 41 is fixed to the front surface of the sewing machine arm 2 via a bracket 40, and its armature 41a protrudes when demagnetized and is retracted when energized.

This second solenoid 41, the thread pay-out lever 30
The needle thread pulling means is constituted by the above. A lock lever 43 is rotatably supported by a stepped screw 42 near the second solenoid 28, and a connecting link 44 is interposed between one arm portion 43a of the lock lever 43 and the armature 41a. The one arm part 43a of the lock lever 43 has a hooking part 43b that can hook the one arm part 30a of the thread letting-out lever 30, and a hook surface 43c that can engage the one arm part 30a of the thread letting-out lever 30. is formed, and a stopper 45 made of a screw is provided on the other arm portion 43d. The lock lever 43 is urged to rotate counterclockwise in FIG. 1 by a spring 46. As shown in FIG. 1, when the second solenoid 41 is demagnetized, the lock lever 43 is rotated to a position where it engages with a stopper 47 on the sewing machine arm 2 due to the biasing force of the spring 46. As shown in FIG. 3, when the second solenoid 41 is energized, the lock lever 43 is rotated a predetermined amount clockwise from the position shown in FIG. Furthermore, when the line letting-out lever 30 is rotated counterclockwise as the first solenoid 28 is energized while the lock lever 43 is regulated in position by the stopper 47, the line letting-out lever 30 is locked. Cam surface 43 of lever 43
c, and after the lock lever 43 is pushed away, it is latched to the latching portion 43b. In the vicinity of the main thread tension device 13, a first release lever 49 serving as thread tension pressure release means is rotated on the front surface of the sewing machine arm 2 by a stepped screw 48. A insertion portion 49a is formed at the tip thereof, and a bifurcated portion 49b that engages with the engagement pin 26a on the lock plate 26 is formed at the intermediate portion. Further, a locking piece 49c is bent at the base end of the first release lever 49, and a stopper 49d made of a screw is attached so as to face the engaging piece 49c. The release lever 49 is urged to rotate counterclockwise in FIG. 1 by a spring 50. The engaging piece 49c and the stopper 49d
A connecting lever 51 is rotatably supported by the stepped screw 48 so as to be located between the stepped screw 48 and the stepped screw 48 . A connecting link 52 is pivotally attached to one end of the arm portion 30a of the thread letting-out lever 30, and the connecting lever 51 is attached to the intermediate portion of the connecting link 52.
The ends are pivotally connected. As shown in FIG. 1, when the first solenoid 28 is demagnetized and the thread pay-out lever 30 is placed in the upper thread release position (the position regulated by the stopper 33), Then, the connecting lever 51 engages with the stopper 49d, and as a result, the first release lever 49 is placed in one position, and its tip end clamping portion 49a is separated from the main thread tension device 13, and the second release lever 49 is placed in one position.
As shown in the figure, when the first solenoid 28 is energized and the thread pay-out lever 30 is placed at the thread pay-out position (approximately horizontal position), the connecting lever 51 is connected to the engagement piece 4.
9c, the first release lever 49 is rotated counterclockwise from the position shown in FIG. The thread tension pressure by the main thread tension device 13 is released. Further, as shown in FIG. 3, when the lock lever 43 with the second solenoid 41 energized is rotated to a position away from the stopper 47, the connecting lever 51 engages with the stopper 45 of the lock lever 43. At the time of engagement, the urging force of the spring 50 and the connecting lever 51 and the stopper 49
d, the insertion portion 49 of the first release lever 49
a) The main thread tension device 13 is held in a state where it is inserted between the thread tension discs 18, and the thread letting-out lever 30 is moved to an intermediate position between the thread releasing position and the thread letting-out position via the connecting link 52. Placed. At this intermediate position, the thread letting-out lever 30 returns to the needle thread supply source in order to pull up approximately half of the surplus thread amount 1. moreover,
When the first release lever 49 is placed in the position shown in FIG. When the engagement piece 26b of 26 is separated from the thread take-up spring 25 and the first release lever 49 is rotated to the position shown in FIG. 2, the lock plate 26 is rotated to the other position and engaged. Piece 26b engages thread take-up spring 25.

A second auxiliary thread tension device 53 is provided on the front surface of the sewing machine arm 2 on the upper thread path between the thread take-up body 11 and the needle 3, and applies thread tension pressure or resistance to the upper thread T1.

The second auxiliary thread tension device 53 has the same structure as the first auxiliary thread tension device 34, including a thread tension shaft 54, a pair of thread tension discs 55, a thread tension spring (not shown), and an adjustment dial 5.
6. And each thread tension device 13
, 34, and 53 are set to become weaker in the order of the main thread tension device 13, the first auxiliary thread tension device 34, and the second auxiliary thread tension device 53. A second release lever 58 is rotatably supported near the second auxiliary thread tension device 53 by a stepped screw 57. This second release lever 58
, the second auxiliary thread tension device 53, etc. constitute a resistance applying means. One arm portion 58a of the second release lever 58 is formed with a recess 58b, and upper and lower insertion portions 58c and 58d located on both upper and lower sides of the recess 58b.
The other end of the connecting link 52 is connected to the other arm 58e of the second release lever 58, and as shown in FIG. 1 and FIG. , the upper and lower insertion portions 58c and 58d of the second release lever 58 are inserted between both thread tension discs 55 of the second auxiliary thread tension device 53 to release the thread tension pressure, and As shown in FIG. 2, when the thread pay-out lever 30 is in the intermediate position, the recess 58b faces both thread tension discs 55, allowing thread tension pressure to be applied. The operation of the sewing machine constructed in this way will be explained with reference to the flowchart shown in FIG. 9.

Now, FIG. 1 shows a state in which the operation pedal (not shown) is depressed forward and sewing operation is being performed.

In this state, the first and second solenoids 28,
41 is demagnetized, and the thread pay-out lever 30 is moved to the stopper 33.
It is regulated by At the same time, the lever 43 is placed in a position where it is regulated by a stopper 47. Therefore, the pinched portion 39a of the release plate 39 is inserted between both thread tension discs 36 of the first auxiliary thread tension device 34, and the thread is held by the first auxiliary thread tension device 34. Pressure is released. Further, the connection lever 51 is rotated clockwise via the connection link 52, and the first release lever 51 is rotated clockwise through the engagement of the connection lever 51 with the stopper 49d of the first release lever 49.
The release lever 49 is rotated clockwise.

As a result, the insertion portion 49a of the first release lever 49 is separated from the main thread tension device 13, and the forked portion 49b of the first release lever 49 and the engagement pin 2 of the lock plate 26 are separated from each other.
6a, the lock plate 26 is rotated counterclockwise, and the engagement piece 26b of the lock plate 26 is separated from the thread take-up spring 25. Therefore, the main thread tension device 13 is in the state of applying thread tension pressure, and the thread take-up spring 25 is in a state of being movable between the first position shown by the solid line in FIG. 7 and the second position shown by the chain line. . Further, the second release lever 58 is rotated clockwise via the connection link 52, and the lower sandwiching portion 58d is inserted between the two thread tension discs 55 of the second auxiliary thread tension device 53, The thread tension pressure of the second auxiliary thread tension device 53 is released. In this state, as the main shaft (not shown) rotates, the needle 3 and the thread take-up body 11 are moved up and down, and when the thread loop catcher 6 is also rotated, the needle 3 and the thread loop catcher 6 work together to move the main shaft. A stitch is formed, and as the thread take-up lever 11 descends during the stitch formation, the thread hooking portion 25a of the thread take-up spring 25 is moved from the second position to the first position by its own spring force. As the slack in the upper thread T1 is absorbed and the thread take-up spring 11'' rises, the thread hooking part 25a of the thread take-up spring 25 resists its own spring force and moves to the first position.
The needle thread is moved from the position to the second position to perform thread tightening, and the insufficient needle thread amount for one pitch corresponding to the feed amount of the work cloth is not affected by the first auxiliary thread tension device 34. The upper thread is fed out from the upper thread supply source.

Therefore, seams with good thread closure are formed on the pressure 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 depressed 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, and the rotation angle of the main shaft is 230°.
When the needle position is reached, a thread trimming signal is generated by a needle 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. 4 is rotated clockwise, and the upper thread T1 and lower thread T2 connected to the work cloth are captured simultaneously.
The yarn is cut after being let out by the amount L+I. On the other hand, when the thread trimming signal is output, the first
The solenoid 28 is energized and the armature 28a is retracted.

Therefore, the thread pay-out lever 30 is rotated counterclockwise from the position shown in FIG. 1, and the cam surface 43c of the lock lever 43 is
After the lock lever 43 is pushed away against the biasing force of the spring 46, it is hooked to the hook portion 43b and locked in the state shown in FIG. When the thread pay-out lever 30 is rotated counterclockwise in this way, the first auxiliary thread tension device 34 is separated from the distal end insertion portion 39a of the release plate 39, and the upper thread is threaded into the first auxiliary thread tension device 34. T1 is clamped. Then, with the subsequent rotation of the thread pay-out lever 30, the upper thread T1 is pulled out from the upper thread supply source side by the above-mentioned thread amount L+l. Also, due to the rotation of the thread letting-out lever 30, the first and second release levers 49, 5 are opened via the connecting link 52, etc.
8 is rotated counterclockwise from the state shown in FIG. entering the club 58
c is inserted between both thread tension discs 55 of the second auxiliary thread tension device 53.

Therefore, the thread tension pressure of the main thread tension device 13 is released, and the second auxiliary thread tension device 53 is also maintained in the state where the thread tension pressure is released, and the thread tension pressure on the needle 3 side is lower than the first auxiliary thread tension device 34. The upper thread T1 is slackened to the extent that it is pulled out by the first auxiliary thread tension device 34, and is in a state where it can be easily let out. Therefore, the thread feeding and cutting operations by the thread cutting mechanism described above are performed smoothly in this state. Furthermore, with the rotation of the first release lever 49, the lock plate 26 is rotated clockwise from the state shown in FIG. 25a
, the threading portion 25a is held in the first position, and its action is nullified.

Then, when the thread cutting mechanism finishes cutting the upper and lower threads Tl and T2 and the main shaft slightly exceeds the rotation angle of 60 degrees, its rotation is stopped and the needle 3 reaches the top dead center. The balance body 11 is stopped at the upper position where it has exceeded and slightly lowered, and the balance body 11 is stopped at 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.
In this state, when the next sewing operation is started by depressing 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 from the top dead center. Formation of a lock stitch on the workpiece cloth is started by the cooperation of the needle 3 and the thread loop catcher 6 as shown in FIG.

Then, when the needle 3 rises through the bottom dead center of the first needle and the balance body 11 reaches the bottom dead center, the detection signal is output and the second solenoid 41 is energized.

Therefore, the lock lever 43 is rotated from the position shown in FIG. 2 to the position shown in FIG. Located within range. When the lock lever 43 is disengaged from the thread letting-out lever 30, the thread letting-out lever 30 is moved to the second position by the biasing force of the spring 32.
The thread is rotated from the thread letting-out position shown in the figure to the thread releasing position shown in FIG. Therefore, the thread letting-out lever 30 is stopped at the intermediate position shown in FIG. 3, and the upper thread T1 is pulled up from the needle 3 side by approximately half of the surplus thread amount 1. Further, the first release lever 49 is engaged with the connecting lever 51 at its stopper 49d, and is held in a state of being inserted into the main thread tension device 13.

Therefore, the thread tension pressure release state of the main thread tension device 13 is maintained, and the locking state of the thread take-up spring 25 is maintained by the lock plate 26. Additionally, a second release lever 58
is rotatably arranged at an intermediate position, and its recessed portion 58b faces the second auxiliary thread tension device 53. Therefore, the second auxiliary thread tension device 53 applies thread tension pressure, that is, resistance, to the upper thread T1 between the thread take-up body 11 and the needle 3. In this state, the thread take-up body 11 is raised from the bottom dead center toward the top dead center, and the excess yarn amount 1
The remaining approximately half of the thread amount is pulled up from the needle 3 side.

Therefore, only the thread amount corresponding to the minimum length L that does not cause thread dropout remains at the sewing start portion of the work cloth, which prevents thread dropout and does not damage the appearance. Also, at this time, since the thread take-up spring 25 is held immovably in the first position by the lock plate 26 etc. as shown in FIG. The thread take-up spring 25 is not moved as the thread take-up spring 25 is moved up and down.
As the thread take-up body 11 rises, the upper thread T1 is removed from the thread ring catcher 6.
The thread loop is reliably picked up, the thread is tightened, and a beautiful seam with a good thread end is formed. This thread take-up spring 25
The action based on the lock is described in Japanese Patent Application No. 55-51505 and Japanese Patent Application No. 51509-1989 filed by the same applicant, so please refer to these for details. Furthermore, in this state, since resistance is applied to the upper thread T1 by the second auxiliary thread tension device 53 as described above, the upper thread T1 increases by the required amount due to its own inertia based on the rise of the thread take-up body 11. The thread will not be pulled up any further, and there is no risk of the thread coming off.

In this way, the first stitch is formed, and the thread take-up body 11
When it reaches the top dead center, the second solenoid 41 is demagnetized, the lock lever 43 is rotated to the position where it is regulated by the stopper 47, and the stopper 45 on the lock lever 43 is rotated.
is separated from the connecting lever 51.

Therefore, the thread pay-out lever 30 is returned to the release position by the biasing force of the spring 30, and the first release lever 49 is returned to the position where it is separated from the main thread tension device 13 via the connection ring 52 and the connection lever 51. Further, the second release lever 58 is connected to the second auxiliary thread tension device 53 at the lower insertion portion 58d.
It returns to the position where it is inserted between both thread tension discs 55. Therefore, the first and second auxiliary thread tension devices 34 and 53 are in the thread clamp holding pressure release state, the main thread tension device 13 is in the thread tension pressure applying state, and the first release lever 49 is in the thread tension pressure applying state. The rotation of the lock plate 26 causes the thread take-up spring 25 to be unlocked. As described above, in this sewing machine, the amount of thread remaining at the beginning of the seam can be optimized.

In the above embodiment, the upper thread T1 was pulled up at the first stitch at the start of sewing, but it is often possible to pull up the upper thread T1 within a few stitches from the second to fifth stitches. can be achieved.

The number of stitches before the effect occurs depends on the thickness of the fabric and the feed pitch, etc. The thinner the fabric and the smaller the feed pitch, the less resistance is applied to the needle thread, so the effect may be delayed from the start of sewing. It is possible to sufficiently pull out the thread even at the right timing. Effects of the Invention As illustrated in the embodiments, the present invention releases the thread tension pressure at least when the thread trimming mechanism is in operation, and cuts the required thread amount by the thread trimming mechanism immediately before the thread trimming operation in the released state. The structure is such that the thread is fed out in advance and an amount smaller than the amount of thread that has been fed out is pulled up from the needle side within a few stitches from the start of the thread take-up mechanism's first thread supply operation at the start of the next sewing. To achieve an excellent effect of optimizing the amount of thread remaining at the beginning of sewing, preventing the thread from coming off at the beginning of sewing, and improving the appearance of the beginning of sewing.

[Brief explanation of the drawing]

1 to 9 show an embodiment of the present invention, in which FIGS. 1 to 3 are front views of the sewing machine arm at the time of sewing, thread trimming, and start of sewing, respectively, and FIG. 4 5 is a sectional view showing the main thread tension device, FIG. 6 is a sectional view showing the first auxiliary thread tension device, and FIG. 7 is a perspective view showing the thread loop catcher and thread trimming mechanism. FIG. 8 is a partial front view showing the main thread tension device in a state where the thread tension pressure is released, and FIG. 9 is a flowchart showing the operation of this sewing machine. Sewing machine arm...2, needle...3, thread loop catcher...1...6, movable blade...10, balance body... 11. Main thread tension device...13.
1st solenoid...28, thread payout lever...
...30, second solenoid ...41,
First release lever...49.

Claims (1)

[Claims] 1 A needle 3 supported vertically movably on an arm 2 of the sewing machine, a thread loop catcher 6 provided on the bed of the sewing machine to form a stitch by cooperation with the needle 3, and the thread loop. A thread cutting mechanism 10, etc., which is provided close to the thread loop catcher 6 and cuts the thread after letting out the required amount of thread at the start of the next sewing at the end of sewing, and the thread loop catcher 6, etc. In order to pick up the thread loop, a thread take-up mechanism 11 etc. provided on the arm 2 is 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. The thread tension device 13 and the thread tension device 13
thread tension pressure release means 49 for releasing the thread tension pressure caused by the thread trimming mechanism 10 at least when the thread trimming mechanism 10 or the like is operated;
etc., is provided on the arm 2 so as to be located on the upper thread path, and is operated immediately before the operation of the thread trimming mechanism 10, etc. in a state in which the thread tension pressure is released by the thread tension pressure release means 49, etc.,
The thread cutting mechanism 10 or the like has a thread letting-out means 28, 30, etc. for letting out the required amount of thread in advance, and a thread amount smaller than the thread amount paid out by the thread letting-out means 28, 30, etc. is used to start the next sewing. An automatic thread trimming sewing machine characterized by being provided with needle thread pulling means 30, 41, etc. for pulling up the needle thread from the needle 3 side within several stitches from the start of the first thread supply operation of the thread take-up mechanism 11, etc.