JPH06335585A - Needle thread cutting device of sewing machine - Google Patents

Abstract

PURPOSE:To provide a needle thread cutting device of a sewing machine, which can increase a cutting timing of a thread, and also, can prevent an interference between a thread cutting means and a cloth holder. CONSTITUTION:This device is provided with a freely openable/closeable thread cutting means 33 fixed to the tip part of a supporting arm 32, a cloth holder 8 which is constituted so that its reciprocating movement is executed freely in linking with a cloth feeding mechanism, and also, in which an opening 7 is formed so as to surround the periphery of a seam and a cloth holding arm 5 having an opening/closing means 15 for opening and closing the thread cutting means 33, a four-link means 24 for moving the supporting arm 32 so that the thread cutting means 33 turns roughly obliquely to the longitudinal directions of the opening 7 by energizing force of an energizing spring 41 and moves freely forward and backward between a retracting position and a cutting position on a vertical motion route of a needle, a holding-up lever 42 for controlling independently the motion of the four-link means 24 by a turning operation, and an actuation safe arm 57 which moves in a sewing machine actuated state and sets the four-link means 24 and a detaining body 43 in an engaged state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a needle thread cutting device for a sewing machine, and more particularly to a needle thread cutting device for a sewing machine which is suitable for a buttonhole sewing machine.

[0002]

2. Description of the Related Art Conventionally, an industrial sewing machine, for example, a buttonhole sewing machine, is provided with a needle thread cutting device that automatically cuts a needle thread (upper thread) after sewing.
It is often used for reasons such as improved sewing efficiency.

As the conventional needle thread cutting device for such a sewing machine, the following two types are known.

The first conventional needle thread cutting device for a sewing machine, as disclosed in, for example, Japanese Utility Model Publication No. 61-5258, has a movable blade which can be opened and closed by a link mechanism in conjunction with the operation of an operating lever. The needle thread (upper thread) is cut by allowing the thread cutting means (scissors) composed of a fixed blade to move forward and backward with respect to the vertical movement path (needle core) of the needle.

A second conventional needle thread cutting device for a sewing machine has scissors that can be moved back and forth in a direction perpendicular to the longitudinal direction of the presser foot with respect to the needle center, and is shown in FIG.

That is, the presser arm 101 supporting the cloth presser 100 for pressing the cloth is rotatably supported at the end portion of the cloth feeding device which is interlocked with the cloth feeding cam which is interlocked with the main shaft (not shown). Has been done.

The cloth presser 100 has a base 100A fixed to the presser arm 101, a plurality of columns 100B vertically provided on the base 100A, and the column 100A.
It is composed of a rectangular frame-shaped cloth pressing body 100C supported at the lower end of B. Then, the cloth pressing body 100C presses the cloth located on the needle plate below the cloth pressing body from above. Further, the base end portion of the support arm 102 is an operation lever 103 pivotally supported by the sewing machine frame.
Scissors 104 that is rotatably supported by and has a fixed blade 104a and a movable blade 104b at its tip end with a step screw.
Is supported so that it can be opened and closed.

To cut the upper thread, the presser foot lifting lever 105 is operated to release the stopper 106 that restrains the support arm 102 from rotating in the horizontal direction, and the coil spring 1 is released.
By the action of 07, the supporting arm 102 is horizontally rotated so that the scissors 104 move forward. Then, the scissors 104 is moved to the cam member 1 during the horizontal rotation of the support arm 102.
By the action of 08, the upper thread which is closed and extends in the vertical direction can be cut.

[0009]

However, in the above-mentioned needle thread cutting device of the first conventional sewing machine, the operation of the thread cutting means is configured to interlock with the operation of the operating lever, and the operating lever is operated. When the thread is cut by the thread cutting means that operates in tandem with the above-mentioned operation, the cutting timing of the thread is delayed, and the thread after the cutting is, for example, Japanese Patent Publication No. 56-6.
With the bobbin thread cutting mechanism of the sewing machine described in Japanese Patent No. 316, it is not possible to secure a sufficient amount when the cloth is pulled into the back side of the fabric, and the thread after cutting remains on the front side stitch of the fabric,
There is a problem that the quality of the sewn product is deteriorated.

Further, in the above-mentioned second conventional needle thread cutting device for a sewing machine, as shown in FIG. 12 (a), in a normal state where the cloth W and the cloth presser 100 are parallel,
Although there is no problem between the scissors 104 and the presser foot 100 during the thread cutting operation, when the cloth retainer 100 is inclined due to the step Wa of the cloth W or the like as shown in FIG. The scissors 104 and the cloth presser 100 during the cutting operation interfere with each other to cause a problem of thread cutting, or both or one of them is damaged or damaged, so that a stable function cannot be maintained for a long period of time. There was a problem.

The present invention has been made in view of these points, and overcomes the above-mentioned problems in the conventional ones.
An object of the present invention is to provide a needle thread cutting device for a sewing machine, which has a simple structure and can speed up the thread cutting timing and prevent interference between the thread cutting means and the presser foot.

[0012]

In order to achieve the above-mentioned object, a needle thread cutting device of a sewing machine of the present invention comprises an openable and closable thread cutting means composed of a fixed blade and a movable blade fixed to the tip of a support arm. , Is reciprocally movable in parallel to the upper surface of the bed in conjunction with the cloth feed mechanism, and has a substantially rectangular opening at its tip end that extends in parallel to the movement direction of the bed and surrounds the seam. Cloth pressing member and a cloth pressing arm having an opening / closing means for enabling the opening / closing operation of the thread cutting means, and the thread cutting means is rotated substantially obliquely with respect to the longitudinal direction of the opening by the urging force of the urging spring. A four-section joint for moving the supporting arm so as to move back and forth between an outer retracted position between longitudinal ends of the opening and a cutting position on the vertical movement path of the needle in the opening. Means and the four-section means The presser foot lifting lever for independently controlling the movement of the four-joint means by a pivoting operation, and the four-joint means and the stopper body that move when the sewing machine is activated. It is characterized in that it is provided with a startup safety arm that is brought into an engaged state.

[0013]

According to the needle thread cutting device of the present invention having the above-mentioned construction, the thread cutting means is operated with the urging force of the urging spring by operating the presser foot lifting lever without interlocking with the operation of the cloth pressing arm. Can be moved back and forth by performing an oblique arc motion from the retracted position to the cutting position.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 to 3 show an embodiment in which the needle thread cutting device for a sewing machine according to the present invention is used in a known buttonhole sewing machine. FIG. 1 is a main part of the needle thread cutting device for a sewing machine. 2 is a plan view showing a main part, and FIG. 3 is a side view of the main part and a perspective view showing a part of the main part.

A buttonhole overedging machine (hereinafter referred to as a sewing machine) 2 equipped with a needle thread cutting device 1 for a sewing machine of the present embodiment,
The bed 3 is arranged in the lower part, and the sewing machine arm 4 is arranged in parallel with the bed 3 in the upper part (FIG. 1).

At a desired position below the sewing machine arm 4, a bent cloth pressing arm 5 is arranged so as to extend substantially parallel to the sewing machine arm 4. This work clamp arm 5
When a sewing operation of the sewing machine 2 is performed, the cloth of the not-shown suture portion is pressed against the upper surface of the bed 3 with a desired pressing force, and the base portion (the left side in the drawing) of the sewing machine 2 is interlocked with a not-shown known cloth feeding mechanism. As indicated by a double-headed arrow A, the reciprocating movement is made in parallel with the upper surface of the bed 3 (the sewing direction) and can be appropriately performed in the left-right direction. The tip of the cloth pressing arm 5 extends below the jaw portion 6 (FIG. 1) of the sewing machine arm 4, and the tip of the cloth pressing arm 5 has a sewing machine suture (not shown) on the upper surface of the bed 3. And a presser bar 8 (FIG. 1) disposed on the jaw part 6 of the sewing machine arm 4 at a lower end of the cloth presser 8 having a substantially rectangular plane opening 7 surrounding the perforated seam (not shown). A shaft 12 (FIG. 1) protruding from the fixed body 11 (FIG. 1) in a direction orthogonal to the longitudinal direction of the presser foot arm 5.
Lifting plate 1 having a notch groove 13 (FIG. 1) loosely fitted in
And 4 are fixed. Further, an appropriate actuating member 15a and a plate cam 15b as an opening / closing means 15 for opening / closing a thread cutting means 33, which will be described later, are arranged at a desired position near the tip of the cloth pressing arm 5.

Further, as shown in FIG. 1, a needle 16 and a known cloth cutting knife 17 for forming a button hole (not shown) are formed above the opening 7 of the cloth presser 8 so as to be movable up and down. It is set up.

At a desired position below the sewing machine arm 4, a fixed plate 18 having a substantially flat plate shape is arranged. The fixing plate 18 is fixed to a desired position of a sewing machine frame (not shown) through an appropriate supporting stay (not shown) so that its longitudinal direction extends substantially parallel to the presser arm 5. Then, in the vicinity of the left and right ends of the fixed plate 18, desired support shafts 19a, 1 are formed in a direction substantially perpendicular to the upper surface of the bed.
9b is provided.

As shown in FIG. 2, on one support shaft 19a shown on the left side of the drawing, a substantially central portion of a substantially bell crank-shaped locking arm 20 in which one arm is a long link 20a is rotated. The other support shaft 19b shown on the right side of the drawing is freely arranged, and the inter-fulcrum length L1 of the long link 20a is provided.
As a result, one end of the short link 21 in the shape of a substantially oblong hole in the plane in which the length L2 between the fulcrums is shortened by a desired length is rotatably arranged.

A long link 20 arranged on the fixed plate 18
The end of a and the other end of the short link 21 are arranged in the direction away from the cloth pressing arm 5, and the end of the long link 20a and the other end of the short link 21 are provided with a step screw or the like. Both ends of a connecting plate 23 having an appropriate shape are rotatably fixed via desired connecting members 22a and 22b. That is, the fixed plate 18 and the connecting plate 23 are connected by the long link 20a and the short link 21 of the locking arm 20 so as to extend substantially parallel to each other to form the four-node means 24.

A desired central standing portion 25 is provided upright so as to be spaced apart from the upper surface of the bed 3 at the substantially central portion and the right end portion of the side surface of the connecting plate 23 in the direction away from the fixed plate 18. And a right end standing portion 26 are formed (FIGS. 1 and 2).

On the right end standing portion 26 of the connecting plate 23, one end of an appropriate connecting link 27 is rotatably supported by a desired connecting member 22c such as a step screw. To the other end of the connecting link 27, one end (right end) of an appropriate connecting support member 28 is arranged so as to extend in parallel with the connecting plate 23 in the longitudinal direction, and is rotated via a desired connecting member 22d such as a step screw. It is rotatably supported. At the other end (left side) of the connection support member 28, an elongated hole 29 penetrating in the plate thickness direction is formed in parallel with the longitudinal direction, and the elongated hole 29 is inserted so as to be loosely fitted. A desired square piece 30 is connected to the central standing portion 25 of the connecting plate 23.

A projecting portion 31 is formed in the upper portion of the connecting and supporting member 28 so as to extend toward the fixed plate 18 (FIG. 2). This protruding part 3
1, a base portion of a bent support arm 32 extending below the jaw portion 6 of the sewing machine arm 4 so as to extend parallel to the cloth pressing arm 5 is rotatably disposed. Thereby, the four-node means 24 and the support arm 32 are connected.

An appropriate thread cutting means (scissors) 33 is provided at a desired position near the tip of the support arm 32.
The thread cutting means 33 includes a fixed blade 34 and a fixed blade 3 on the fixed blade 34 via a desired connecting member 22e such as a step screw.
4 and a movable blade 35 (FIG. 2) having a substantially bell-crank shape, which is arranged so as to open and close the opposite edge thereof. And
An appropriate pin 36 is arranged at a desired position on the left side of the movable blade 35.

As shown in FIG. 2, at a desired position facing the cloth pressing arm 5 at a substantially central portion in the longitudinal direction of the support arm 32, the connecting plate 23 extends from the substantially central portion toward the fixing plate 18. One end is locked in a locking hole 38 formed in the central protruding portion 37, and a stopper pin 39 is provided upright at a desired position on the right side of the locking hole 38 of the central protruding portion 37 in the drawing. The free end of the desired spring member 40, which is arranged so as to be in contact with the surface on the side separated from the fixed plate 18, is in contact with the support arm 32, and the support arm 32 has a cloth centering on the connecting member 22f. It is always urged in a direction away from the presser arm 5 (clockwise in FIG. 2).

The engaging hole 38 of the connecting plate 23 is engaged with the other end of an appropriate urging spring 41 whose one end is engaged with a sewing machine frame (not shown), and the connecting plate 23 and the connecting support member 28. The support arm 32 and the thread cutting means 33 arranged at the tip of the support arm 32 are constantly urged in the direction of approaching the cloth pressing arm 5.

As shown in FIGS. 1 and 2, a desired presser foot lifting lever 42 is disposed on the left side of the fixed plate 18 so as to be orthogonal to the longitudinal direction of the cloth presser arm 5. The fixed end of the presser foot lifting lever 42 is rotatably supported by a sewing machine frame (not shown). An appropriate locking body 43 is rotatably arranged at a desired position on the side surface of the presser foot lifting lever 42 facing the fixed plate 18. The locking body 43 includes a shaft member 44 having an axial center extending in a direction orthogonal to the longitudinal direction of the presser foot lifting lever 42 (direction parallel to the fixed plate 18), and the presser foot lifting lever 42 of the shaft member 44.
Member 45 having a protruding portion fixed to a desired position on the side in a direction parallel to the presser foot lifting lever 42 (direction orthogonal to the axial center direction of the shaft member 44), and a presser foot lifting lever at the tip of the shaft member 44. A desired L-shaped locking piece 46 fixed in a direction parallel to 42 (a direction orthogonal to the axial direction of the shaft member 44).
And (see FIGS. 3A and 3B).

Further, a desired torsion spring 47 is provided on the outer peripheral surface of the shaft member 44 between the member 45 and the presser bar lever 42.
Is provided, one end of the torsion spring 47 is locked to the member 45, and the other end is locked to the presser lever 42. The torsion spring 47 constantly urges the locking body 43 to rotate counterclockwise (FIG. 3A). The locking body 43 biased in the counterclockwise direction by the torsion spring 47 projects from one end of the member 45 of the locking body 43 and a desired position on the side surface facing the fixed plate 18 of the presser foot lifting lever 42. The rotation position in the counterclockwise direction is constrained by the contact with the desired locking pin 48. The side surface of the tip of the locking piece 46 of the locking body 43 facing the presser-up lever 42 and the side surface of the free end 20b of the locking arm 20 are disengageable to form a latch mechanism. , The free end 20b of the locking piece 46 and the locking arm 20
When and are located in the locked state, the connecting plate 23 is immovable. Furthermore, an appropriate rotatable roller member 49 is disposed at a desired position on the free end side of the position where the locking body 43 of the presser foot lifting lever 42 is disposed.

At a desired position on the side of the presser foot lifting lever 42 facing the fixed plate 18 (left side in FIGS. 1 and 2),
A desired arm member 50 is arranged so as to extend parallel to the presser bar lifting lever 42. This arm member 50
Is arranged so that its base is rotatable on a sewing machine frame (not shown). A through groove 51 (FIG. 3A) having an appropriate shape is formed below the arm member 50, and the roller member 49 is inserted into the through groove 51 in a non-contact state. . In this through groove 51, FIG.
As shown in (a), a desired small width portion 51a extending in the vertical direction in the drawing and having a lower portion formed in a relatively narrow width substantially the same as the outer dimensions of the roller member 49, and from above the small width portion 51a. A desired large portion 51b having a width larger than the outer dimension of the roller member 49 is formed diagonally upward to the right. On the lower right side of the arm member 50, a base portion 52 extending in parallel with the arm member 50 and the base portion 5 are provided.
The base portion 52 of the sub-stay 54, which is formed in a generally inverted L-shape on the front (FIG. 1) as a whole, is fixed by an upright portion 53 that is upright from the upper end of the arm member 50 in a direction away from the arm member 50.

Both ends of a desired link 56 are connected between the upright portion 53 of the substay 54 of the arm member 50 and a desired position of the connecting plate 23 via appropriate ball joints 55, 55. .

A desired starting safety arm 57 is arranged above the locking arm 20 (FIG. 1). The start-up safety arm 57 is pivotally supported such that its base portion interlocks with a start-up pedal of a sewing machine (not shown), and its free end is shown in FIG.
In, it is rotatable in the left-right direction. Then, at the free end of the activation safety arm 57, the presser foot lifting lever 42 of the free end 20b of the locking arm 20 is moved by the movement of the activation safety arm 57.
A locking arm actuating portion 58 is formed so as to be able to come into contact with and separate from an upper portion of a side surface located far from (see FIG. 3A).

Next, the operation of this embodiment having the above-mentioned structure will be described with reference to FIGS.

FIGS. 1 to 3 show a state before the thread trimming (when the thread is cut off) immediately before the thread trimming is completed after the sewing of the buttonhole stitches by the sewing machine is completed, and FIG. 4 explains the thread trimming state. FIG. 5 is a view similar to FIG. 3A, FIG. 5 is a view similar to FIG. 2 illustrating a thread cutting state, and FIG. 6 is a view similar to FIG. 3A illustrating a presser foot lifting state. 7 is a view similar to FIG. 2 for explaining the presser foot lifted state, and FIG. 8 is a view similar to FIG. 3 (a) for explaining the state before the sewing machine is activated,
9 is a view similar to FIG. 2 for explaining the sewing machine starting state, and FIG. 10 is a view similar to FIG. 2 for explaining the open state of the movable blade in the sewing machine starting state.

As shown in FIGS. 1 to 3, when the sewing of the buttonhole overlock stitch by the sewing machine 2 is completed and the thread is cut immediately before thread cutting (when the thread is cut off), the needle 16 moves up and down. It is located above the path (needle core) and stopped, and a needle thread (upper thread) (not shown) is connected between a stitch (not shown) and the needle 16. Then, as shown in FIG. 3A, the presser foot lifting lever 42 and the activation safety arm 57 are not operated and are in a stopped state. Furthermore, FIG.
And as shown in FIG. 3A, the locking piece 4 of the locking body 43.
The side surface of the tip end 6 of the locking arm 6 facing the presser-up lever 42 and the side surface of the locking arm 20 near the free end 20b are engaged with each other, and the connecting plate 23 is immovable. Also,
The movable blade 35 of the thread cutting means 33 is opened, and the movable blade 35 is positioned between the both ends of the opening 7 of the cloth presser 8 in the longitudinal direction at the retracted position which is most obliquely separated from the vertical movement path (needle center) of the needle. There is.

Next, when the presser foot lifting lever 42 in the state before thread cutting shown by the solid line in FIG. 3A is rotated in one direction to the position shown by the broken line, the presser foot lifting lever 42 moves the fulcrum P1. It rotates counterclockwise about the center as shown by arrow B, whereby the parts shown in FIG. 3 (a) move as shown in FIG. 4 and the parts shown in FIG. 2 move as shown in FIG. The thread cutting means 33 in the retracted position advances obliquely to the desired cutting position on the needle center of the needle 16 according to the four-node means 24, and the movable blade 35 rotates to move to the fixed blade 34. Causes the upper thread (not shown) to be cut.

That is, when the presser foot lifting lever 42 rotates, the tip of the locking piece 46 of the locking body 43 also presses the presser foot lifting lever 4.
Rotate counterclockwise around the fulcrum P1 as in 2,
As a result, the tip of the locking piece 46 of the locking body 43 is separated from the side surface of the free end 20b of the locking arm 20, and the locking body 43
The engagement state between the side surface of the tip of the engagement piece 46 facing the presser-up lever 42 and the side surface of the free end 20b of the engagement arm 20 is released. Then, by the biasing force of the biasing spring 41 shown by the arrow C in FIG. 5 applied to the connecting plate 23, the locking arm 20 and the short link 21 are respectively supported by the support shafts 19a and 19a.
While rotating in the counterclockwise direction about b, the connecting plate 23 has a length L between the fulcrums of the long link 20a of the locking arm 20.
1 and the length L2 between the fulcrums of the short link 21 move to the right and the upper side while being restrained with the length L2 between the fulcrums, and the thread cutting means 33 also similarly moves via the support arm 32 arranged on the connecting plate 23
The pin 36 arranged at a desired position on the left side of the movable blade 35 of the thread cutting means 33 is in contact with the operating member 15a of the opening / closing means 15 arranged at a desired position near the tip of the cloth pressing arm 5. When the movable blade 35 comes into contact with the movable blade 35 and rotates in the counterclockwise direction about the connecting member 22e to close it, the upper thread (not shown) can be sandwiched and cut in cooperation with the fixed blade 34. That is, as shown by an arrow D in FIG. 5, the tip of the fixed blade 34 of the thread cutting means 33 moves from the outer retracted position between the longitudinal ends of the opening 7 of the cloth presser 8 toward the cutting position on the needle center. Move forward while making a diagonal arc motion.

The link 5 is moved by the movement of the connecting plate 23.
The arm member 50 connected via 6 pivots counterclockwise about the fulcrum P2, and each part is brought into the state (thread cutting state) shown in FIGS. 4 and 5.

In the thread cutting state, the arm member 5
When 0 rotates counterclockwise about the fulcrum P2, the roller member 49 provided on the presser foot lifting lever 42 is
The arm member 50 is located in the large portion 51b in the through groove 51 in a non-contact state.

Next, when the presser foot lifting lever 42 in the thread cutting state shown by the broken line in FIG. 3A is further rotated in one direction to the position shown by the alternate long and short dash line, the presser foot lifting lever 4 is moved.
2 further rotates counterclockwise around the fulcrum P1,
As a result, the respective parts shown in FIGS. 4 and 5 move as shown in FIGS. 6 and 7 to be in the presser-lifting state, and the thread cutting means 33 located at the cutting position returns to the retracted position in the closed state.

That is, by rotating the presser foot lifting lever 42, the tip of the locking piece 46 of the locking body 43 also presses the presser foot lifting lever 4.
As in the case of 2, the roller member 49 further rotated counterclockwise about the fulcrum P1, whereby the roller member 49 disposed on the presser foot lifting lever 42 causes the narrow width portion 51 in the through groove 51 of the arm member 50.
6A and moves to contact the arm member 50,
As indicated by arrow E, the fulcrum P2 is rotated clockwise. Then, as shown by the arrows in FIG. 7, each part of the connecting plate 23 and the like connected to the arm member 50 via the link 56 operates in the direction opposite to the above-described operation direction at the time of thread cutting, and the thread cutting operation is performed. The tip of the fixed blade 34 of the means 33 retreats from the cutting position on the needle center toward the outer retreat position between the longitudinal ends of the opening 7 of the presser foot 8 while performing a substantially circular arc motion.

Next, when the presser foot lifting lever 42 in the presser foot lifted state shown by the one-dot chain line in FIG. 3 (a) is returned to the state before thread cutting shown by the solid line in FIG. 3 (a), the presser foot is lifted. The lever 42 moves clockwise (arrow B) about the fulcrum P1.
(In the opposite direction), whereby each part shown in FIG. 3A is in the state before the sewing machine is started as shown in FIG.

That is, by the rotation of the presser foot lifting lever 42, the tip of the locking piece 46 of the locking body 43 is held in contact with the lower part of the locking arm 20 near the free end 20b, and the presser foot is raised. Locking pin 48 of lever 42 and locking body 4
The member 45 of No. 3 is separated.

Next, when the start pedal of the sewing machine (not shown) is operated before the start of the sewing machine, the start safety arm 57 rotatably arranged on the sewing machine frame (not shown) is interlocked with the start pedal and the fulcrum P3. The center of the sewing machine rotates clockwise (FIG. 1) to enter the sewing machine starting state shown in FIG.

That is, the locking arm actuating portion 58 at the bottom of the start-up safety arm 57 abuts on the vicinity of the free end 20b of the locking arm 20, and the locking arm 20 rotates clockwise about the support shaft 19a, The state in which the tip of the locking piece 46 of the locking body 43 is in contact with the lower part of the locking arm 20 near the free end 20b is released. When the desired sewing progresses, the cloth pressing arm 5 reciprocates as shown by a double-headed arrow F in FIG. 9, and the plate cam 15b of the opening / closing means 15 arranged on the cloth pressing arm 5 is reciprocated by this reciprocating motion. The pin 36 of the movable blade 35 is brought into contact with the thread cutting means 33 from the opposite direction to the one surface 33a of the thread cutting means 33 and the plate cam 1.
The movable blade 35 can be brought into an open state as shown in FIG. 10 by rotating the connecting member 22f as a center until the 5c abuts.

When one cycle of desired sewing is completed in the sewing machine activated state, the activation safety arm 57 rotates counterclockwise around the fulcrum P3 (FIG. 1) and returns to the original position. In this case, the locking arm 20 also tries to rotate counterclockwise by the biasing force of the biasing spring 41, but the locking body 43
The side surface of the tip of the locking piece 46 facing the presser foot lifting lever 42 and the side surface near the free end 20b of the locking arm 20 are in a locked state, and each portion is before thread cutting shown in FIGS. 1 to 3. Return to the position of each state.

Therefore, according to the present embodiment, the thread trimming can be performed by independently rotating the presser foot lifting lever 42 without interlocking with the operation of the cloth presser arm 5 which interlocks with the known cloth feeding mechanism. Since the operation of the means 33 can be controlled, the timing of cutting the needle thread can be surely advanced, the residual amount of the needle thread on the stitch can be surely reduced, and the quality of the sewn product can be surely improved. You can

In addition, the thread trimming means 33 is attached to the opening 7 of the presser foot 8.
When the cloth presser 8 is tilted, it can move back and forth by performing an oblique circular arc motion from the outer retracted position between both ends in the longitudinal direction toward the cutting position on the vertical movement path (needle center) of the needle. Interference between the thread cutting means 33 and the presser foot 8 can be surely prevented to prevent a thread cutting defect from occurring, and damage or breakage of both or one of them can be surely prevented, which results in long-term operation. It is possible to maintain a stable function over a period of time.

The present invention is not limited to the above embodiment, but can be modified as necessary.

[0050]

As described above, according to the needle thread cutting device for a sewing machine of the present invention, thread cutting is performed by independently rotating only the presser foot lifting lever without interlocking with the operation of the cloth pressing arm. Since the operation of the means can be controlled, the needle thread cutting timing can be reliably advanced, the residual amount of needle thread on the stitch can be reliably reduced, and the quality of the sewn product can be reliably improved. In addition, it is possible to move back and forth by performing an oblique circular motion from the retracted position to the cutting position, so that it is possible to reliably prevent interference between the thread trimming means and the cloth presser when the presser foot tilts, and to perform thread trimming. This has an extremely excellent effect that it is possible to reliably prevent the occurrence of defects and maintain a stable function for a long period of time.

[Brief description of drawings]

FIG. 1 is a front view showing an essential part of a needle thread cutting device for a sewing machine according to the present invention before thread cutting.

FIG. 2 is a plan view of a main part of FIG.

3A is a side view of a main part of FIG. 1, and FIG. 3B is a perspective view showing a part of the main part.

FIG. 4 is a view similar to FIG. 3A for explaining a thread cutting state.

FIG. 5 is a view similar to FIG. 2 for explaining a thread cutting state.

FIG. 6 is a view similar to FIG. 3A for explaining a presser foot lifting state.

FIG. 7 is a view similar to FIG. 2 for explaining the presser foot lifting state.

FIG. 8 is a view similar to FIG. 3A for explaining a state before the sewing machine is started up.

FIG. 9 is a view similar to FIG. 2 for explaining a sewing machine starting state.

FIG. 10 is a view similar to FIG. 2 for explaining an open state of the movable blade when the sewing machine is activated.

FIG. 11 is a plan view showing a needle thread cutting device of a second conventional sewing machine.

12A and 12B are views for explaining a thread cutting state of a needle thread cutting device of a conventional sewing machine, FIG. 12A is a front view of a main portion for explaining a normal state, and FIG. 12B is a main portion for explaining an interference state. Front view of

[Explanation of symbols]

 1 Needle thread cutting device of the sewing machine 5 Cloth presser arm 7 Opening 8 Cloth presser 15 Opening / closing means 15a Operating plate 15b Plate cam 18 Fixing plates 19a, 19b Spindle 20 Locking arm 20a (locking arm) long link 20b (locking) Free end of arm 21 Short link 23 Connection plate 24 Four-node means 27 Connection link 28 Connection support member 32 Support arm 33 Thread cutting means 34 Fixed blade 35 Movable blade 36 Pin 41 Energizing spring 42 Presser lever 43 Locking body 46 Locking piece 49 Roller member 50 Arm member 51 Through groove 51a Small width part 51b Large part 56 Link 57 Start safety arm 58 Locking arm operating part P1, P2, P3 fulcrum

Claims (1)

[Claims] 1. An openable and closable thread trimming means comprising a fixed blade and a movable blade fixed to the tip of a support arm, and a tip that is reciprocally movable in parallel with the bed upper surface in conjunction with a cloth feeding mechanism. Cloth having a cloth retainer having a substantially rectangular opening formed in a plane so as to surround the seam and extending parallel to the moving direction of the cloth, and an opening / closing means for enabling the opening / closing operation of the thread cutting means. The pressing arm and the thread cutting means are rotated substantially obliquely with respect to the longitudinal direction of the opening by the urging force of the urging spring so that the outer retracted position between both ends of the opening in the longitudinal direction and the inside of the opening. The four-joint means for moving the support arm so as to move back and forth between the cutting position and the cutting position on the up-and-down movement path of the needle; Independent movement of the knot means by turning operation A needle thread cutting device for a sewing machine, comprising: a presser foot lifting lever to be controlled; and a starting safety arm that moves in a sewing machine starting state to engage the four-node means and the locking body.