JP2003230785A - Thread cutting device for sewing machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To evade a capture miss and to reliably show a prescribed thread cutting function by simply improving a structure, i.e. changing the movement locus of a cutting edge in a lower knife without the need for drastic alternation even when a seam pitch is coarse and a sewing without material is an object to be cut. <P>SOLUTION: A thread cutting device comprises an inclination guide surface 30 for guiding a lower knife base 15 to move in an inclining direction so as to gradually enlarge a distance from a straight line route in a direction B perpendicularly crossed with a sewing progress direction A according as the cutting edge movement locus of the lower knife 1 approaches a progress position, by allowing the lower knife 1 and the lower knife base 15 to come slidable contact with the projection 15c of the lower knife base 15 when moved forward to the progress position from a middle position where the movement of an upper knife 2 is stopped along the straight line route in the direction B perpendicularly crossed with the sewing progress direction A. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thread cutting device of a sewing machine mainly applied to a double chain stitch sewing machine or a flat stitch sewing machine. Specifically, at the time when sewing with the sewing machine is completed, the needle thread (upper thread) located between the needle plate with which the back surface of the material contacts and the looper that moves in the direction orthogonal to the sewing traveling direction at the lower part of the needle plate, and When both the looper thread (bobbin thread) or the material is sewn to its edge, the empty ring formed in a continuous continuous state from the lower part of the needle plate to the upper surface of the needle plate along the sewing progress direction is used as the needle plate and the looper. The present invention relates to a thread cutting device for a sewing machine, which is configured to pull out from a space between them to a lateral position orthogonal to the sewing traveling direction and cut.

[0002]

2. Description of the Related Art A thread cutting device for this type of sewing machine is shown in FIG.
As shown in FIG. 13, a first knife (hereinafter referred to as a lower knife) 1 having hook-shaped thread catching portions 1a and 1b for hooking a needle thread NY and a looper thread LY at the tip, and the lower knife 1 Has a blade edge 2a for cutting the needle thread NY and the looper thread LY caught by the thread catching sections 1a, 1b by a sliding contact action with the thread catching sections 1a, 1b, and among the cut ends of the looper thread after cutting. A second knife (hereinafter referred to as an upper knife) 2 having a thread clamping spring 4 for clamping and holding an end portion connected to the looper 3 and a lower knife 1 with their thread catching portions 1a and 1b in a sewing advancing direction A. As shown in FIG. 12, the standby position retracted to the side of the operating path of the looper 3 that moves in the direction orthogonal to the needle 9 and the needle 9 that reciprocates up and down so as to penetrate the cloth W (shown by two needles). ) And is brought to the back side of the cloth W through the needle plate (Fig. Of the lower knife 1 and a lower knife drive mechanism for reciprocatingly driving the needle thread loop NY-L formed below the needle thread loop NY-L in a direction orthogonal to the sewing advancing direction A. There is provided an upper knife linkage moving mechanism that follows the reciprocating movement between the standby position and the forward movement position to reciprocate the upper knife 2 between the standby position and the midway position before the forward movement position. Since the lower knife drive mechanism and the upper knife linkage moving mechanism have basically the same configurations as those described in detail in the embodiments of the present invention described later, a detailed description thereof will be omitted here.

In the thread cutting device of the sewing machine having the above-mentioned structure, the lower knife 1 and the upper knife 2 and the looper 3 are actuated by the operation of the lower knife driving mechanism and the upper knife linking moving mechanism when the sewing is completed. As shown in FIG. 11, the vehicle moves forward from the standby position retracted to the side of the route to a midway position before the forward movement position. At this position, the movement of the upper knife 2 is stopped, and only the lower knife 1 continues to move forward (forward) toward the forward position, and as shown in FIG. 14, plunges into the needle thread loop NY-L. The yarn catching portion 1b on the tip end side reaches the forward position by passing in front of the looper yarn LY that is slantingly stretched between the cloth W and the tip of the looper 3. Then, as clearly shown in FIG. 15, the lower knife 1 starts the return (return) movement from the forward position to the midway position, and at the time of the return movement, as shown in FIG.
The needle thread NY and the looper thread LY are hooked (captured) with a and 1b. Then, as shown in FIG. 13, the lower knife 1 is moved back to the midway position, and the thread catching portions 1a and 1b are slidably contacted with the blade edge 2a at the tip of the upper knife 2 as shown in FIG. NY and looper thread LY are cut, and needle thread N
The cut end portion of Y is not held, while the cut end portion of the cut end portion of the looper thread LY which is continuous with the looper 3 is sandwiched and held between the lower knife 1 and the thread clamp spring 4 to prepare for the next sewing. Get ready. After that, the upper and lower knifes 2, 1 return together to the standby position.

In the thread cutting device of the sewing machine having the above-described structure and operation, the most advanced movement locus of the lower knife 1 during the reciprocating movement between the standby position and the forward movement position is conventionally shown in FIG. Was configured as. That is, after the movement of the upper knife 2 is stopped, the locus of movement of the distal end portion 1c during the forward movement of the lower knife 2 from the intermediate position p1 to the forward position p2 and the return movement from the forward position p2 to the intermediate position. Fig. 16 shows all the movement trajectories of the leading edge 1c at the time.
As indicated by the solid line, the line was set (configured) in a straight line along a straight line path in a direction orthogonal to the sewing advancing direction A.

[0005]

A lower knife 1 configured to reciprocate along the leading edge movement locus as described above.
In the conventional thread cutting device of the sewing machine, when the stitch pitch P (see FIG. 11) with respect to the fabric W is roughly set, the sewing advancing direction A per needle of the fabric W set on the needle plate 6 is increased. As a result, the amount of feeding of the needle thread loop NY-L, which is obliquely stretched between the cloth W and the tip of the looper 3, is increased as shown by the dotted line in FIG. Is larger than the inclination in the case of the normal stitch pitch as shown by the solid line, and the position of the needle thread portion to be hooked by the thread catching portions 1a and 1b is displaced to the rear side in the sewing advancing direction A, The yarn catching portions 1a and 1b of the lower knife 1 are moved from the forward movement position p2 along a straight line path to a middle position p.
When returning to 1, the yarn catching portions 1a and 1b are apt to cause a catching error such that the yarn catching parts cannot be surely caught (hooked), and as a result, a predetermined yarn cutting action cannot be performed. .

Such a thread catching mistake and a cutting mistake are not limited to when the stitch pitch P is coarse, but when the material is sewn up to the edge thereof, as shown in FIG. 18, from the looper 3 below the needle plate 6. An empty ring K formed over the upper surface of the needle plate 6 in a continuous continuous state substantially along the sewing advancing direction A (the sewing operation after the material W is moved past the needle drop portion 5 by the feed of the front and rear feed teeth 7 and 8). Along with this, thread waste formed by the entanglement between the needle thread NY and the looper thread LY) is hooked and cut by the thread catching portion 1b of the lower knife 1 which projects into a narrow space between the needle plate 6 and the looper 3. Also in this case, the inclination of the needle thread loop NY-L forming the empty ring K becomes large and the position of the thread portion to be hooked shifts to the rear side in the sewing advancing direction A as shown in FIG. This is a problem that will be raised.

That is, in the conventional thread cutting device in which the locus of movement of the lowermost knife 1 is set (configured) in a straight line along the straight line path in the direction orthogonal to the sewing advancing direction A as described above, Since the range is narrow, there is a problem in that, when the stitch pitch P is roughly set and when the empty ring K is set as a cutting target, a catching error is caused and a predetermined thread cutting action cannot be performed. .

The present invention has been made in view of the above circumstances, and the seams can be made by a very simple structural improvement by merely changing the trailing locus of movement of the lower knife without requiring a major modification of the basic structure. For the purpose of providing a thread cutting device for a sewing machine, which can avoid occurrence of a catching error and can secure a predetermined thread cutting function in both cases where the pitch is rough and the object to be cut is an empty ring. There is.

[0009]

In order to achieve the above object, a thread cutting device for a sewing machine according to the present invention includes a lower knife having a thread catching portion for hooking a needle thread and a looper thread at its tip, and a lower knife. An upper knife that cuts the thread caught in the thread catching section of the knife, a standby position where the thread catching section at the tip of the lower knife is retracted to the side of the looper operation path, and a forward position where the needle thread loop is projected. And a drive lever reciprocally swingably mounted on the knife mounting portion so as to be reciprocally driven to move in a direction orthogonal to the sewing advancing direction, and the lower knife is linked to the reciprocating swing of the drive lever. In a thread cutting device of a sewing machine, which has a mechanism for reciprocating the upper knife to follow the lower knife when reciprocating to a middle position before the standby position and the forward position, the lower knife is orthogonal to the sewing advancing direction. Up along a straight path When moving forward from the midway position to the forward position, the locus that guides the forward movement of the lower knife such that the leading edge of the locus gradually deviates to the rear side in the sewing advancing direction with respect to the straight line path as it approaches the forward position. It is characterized in that a changing means is provided.

According to the present invention having the above-mentioned structure, when the lower knife, which has moved forward together with the upper knife to the midway position, independently moves forward from the midway position to the forward movement position, the leading edge movement locus approaches the forward movement position. , Since it is inclined so as to gradually separate from the straight line path in the direction orthogonal to the sewing advancing direction to the rear side in the sewing advancing direction, when the lower knife returns from the forward position to the intermediate position, the thread at the tip of the lower knife is The catching portion is returned and moved through a position on the rear side in the sewing advancing direction with respect to the straight line path, so that the thread catching range becomes wider in the sewing advancing direction. Therefore, the needle thread and the looper thread to be caught and cut may be sewn with a coarse stitch pitch such that the needle thread and the looper thread are displaced to the rear side in the sewing progress direction, or when the empty ring as described above is to be cut. Also, it is possible to surely catch the needle thread and the looper thread or the empty ring by the thread catching portion without any mistake and to pull them out to the side and cut them in a predetermined manner by the upper and lower knife.

In the thread cutting device of the sewing machine according to the present invention, as described in claim 2, it is formed on the lower knife table so as to guide the reciprocating movement of the lower knife between the standby position and the forward position. A notch is formed on a part of one edge of the long hole that is fixed to the knife mounting part so as to guide the outward movement of only the lower knife after the upper knife has stopped moving at the midway position. The lower knife table guide member is formed with an inclined guide surface such that the distance from the straight line path in the direction orthogonal to the sewing advancing direction gradually increases as it approaches the forward movement position. By forming the above-mentioned movement locus changing means with the notch formed in a part of the above, the notch is formed at a part of the long hole edge which is a part of the lower knife drive mechanism and the upper knife linkage moving mechanism. And tilt guide on the lower knife table guide member To make effective use of most of the conventional mechanisms without making major modifications to the basic structure of the mechanisms that were also used in conventional devices, and to make extremely simple structural improvements. Alone
As described above, the trailing locus of the lower knife can be changed to a locus without a yarn catching error, and the reliability of yarn catching and yarn cutting can be improved while minimizing the cost increase.

Here, the inclined guide surface formed on the lower knife table guide member may be a fixed sliding contact surface which is not elastically deformed. Particularly, as described in claim 3, a leaf spring is used. The sliding contact guide surface, which is elastically deformable, elastically absorbs the impact when the lower knife table that moves at a relatively high speed collides with the inclined guide surface and mechanical vibrations during the sliding contact guide. Since the lower knife table can be moved and guided in the inclined direction while absorbing and relaxing, the predetermined trajectory change can be smoothly and reliably performed without shock, and
By selecting the spring constant of the leaf spring, it is possible to properly and arbitrarily adjust the trailing locus of movement of the lower knife in accordance with the stitch pitch and the like to further secure the thread catching performance.

A mechanism for reciprocally moving the lower knife between the standby position and the forward position in association with the reciprocating swing of the drive lever is described in claim 4 and will be described in detail in the embodiments described later. As described above, the reciprocating movement direction is sandwiched between the lower lever and the drive lever reciprocally swingably attached to the female attaching portion so as to reciprocally drive the lower knife between the standby position and the forward position. Preferably, the knife guide lever links are arranged on both sides of the above and springs provided to urge the upper knife to move in the forward direction, but in addition to this, for example, Japanese Patent Publication No. Sho 61-9080. As disclosed in the official gazette, etc., the elongated holes formed by arranging the lower knife table on both sides in the reciprocating direction with the point of linkage with the drive lever interposed therebetween are formed in a substantially V shape, Female attachment inside the long hole A guide protrusion such as a pin projected from the above is loosely fitted, and in cooperation with the reciprocating swing of the drive lever, a sliding movement between the guide hole and the substantially V-shaped long hole allows the lower knife to move in a desired locus. It may be configured to guide the reciprocating movement as drawn.

The distance between the tip of the lower knife and the straight path when the lower knife moves forward to the forward position is 0.5 to 3 mm in accordance with the stitch pitch size and the like.
It may be set arbitrarily within the range.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment,
The same components as those described with reference to FIGS. 11 to 15 will be denoted by the same reference numerals, and the same components will be described while omitting part of the specific configuration.

FIG. 1 is an exploded perspective view of a thread cutting device for a sewing machine according to the present invention, FIGS. 2 to 5 are overall plan views for explaining an operating state of the thread cutting device, and FIG. 6 is a front view of FIG. . As described above, this thread cutting device has a lower knife 1 having hook-shaped thread catching portions 1a and 1b for hooking the needle thread NY and the looper thread LY at the tip, and the thread catching portion 1a of the lower knife 1. An upper knife 2 having a blade edge 2a for cutting the needle thread NY and the looper thread LY captured by the thread 1b by sliding contact with the thread catching portions 1a, 1b, and a looper 3 of the cut ends of the looper thread after cutting. And the side of the operating path of the looper 3 in which the thread catching spring 4 for sandwiching and holding the end portion connected to the lower knife 1 and the lower knife 1 move in the direction B in which the thread catching portions 1a and 1b thereof are orthogonal to the sewing advancing direction A. Is reciprocally driven in the direction B orthogonal to the sewing advancing direction A between the standby position retracted to and the forward position projected into the needle thread loop NY-L formed below the needle plate (not shown). Lower knife drive mechanism to move and the above waiting of lower knife 1 Position and by following the reciprocating movement between the advanced position and comprising a female linking moving mechanism on to reciprocate over between the upper knife 2 to an intermediate position before the forward position and the standby position.

The lower knife drive mechanism and the upper knife linkage moving mechanism are constructed as follows. That is, the female mounting plate portion 12 fixed to the sewing machine bed 11 has an intermediate portion at the shaft rod 1
A drive lever 14 pivotally supported by 3 is configured to be reciprocally driven and swingable around the shaft rod 13 via an expansion / contraction drive device such as a cylinder (not shown). A U-shaped cut into which a circular engaging portion 14a formed at the tip of the drive lever 14 is fitted to one side of the center of the lower knife table 15 to which the lower knife 1 is fixedly connected by screwing. A notch 15a is formed, and straight long holes 15r, 151 for guiding the reciprocating movement of the lower knife 1 and the lower knife table 15 are formed at both left and right sides of the notch 15a, and A projection 15b is provided on one side portion of the lower knife table 15 near the left end, and a lower knife table guide (lower knife table guide member) 16 fixed to the sewing machine bed 11 by screws on the other left edge part. Protrusion 15 that is fixed to the lower female base stopper 17 and is adjacent to the protrusion 17a of the stopper 17
c is formed to project.

On the other hand, the upper knife 2, the thread pinching spring 4,
The lower knife guide 18, the thread-clamping spring adjusting spring 19, the thread-clamping spring adjusting spring presser plate 20, and the thread-clamping spring pressing adjusting piece 21 are fixed by screws. An engaging protrusion 22b that engages with the right end edge of the protrusion 15b of the protrusion 15 is projectingly formed, and an upper knife holder stopper 23 screwed and fixed to the knife mounting plate 12 is formed on the other side of the center slightly to the right. An engaging protrusion 22a is formed so as to protrude from the upper knife 2 and the upper knife table 22 by engaging with the. In addition, screw holes 22r, 22 are provided at a position slightly to the right of the center of the upper knife table 22 and near the right end, respectively.
1 is formed.

Further, the female attachment plate portion 12 is provided with eccentric pin 25r, 2 with a brim, which is screwed to the attachment plate portion 12.
A pair of left and right female guide lever links 24 via 5l
r and 24l are pivotally attached to each other. Pins 26r and 26l with flanges that fit into the left and right elongated holes 15r and 15l formed in the lower female table 15 are rotatably inserted and held at the free ends of the left and right female guide lever links 24r and 24l. The flanged pins 26r and 26l are screwed into the screw holes 22 of the upper female table 22 via screws 27r and 27l.
It is screwed to r and 22l. Furthermore, upper knife stand 2
One end of an upper knife base spring 28 screwed to the knife mounting plate portion 12 is locked to the engaging protrusion 22a of No. 2, and the elastic force of this spring 28 causes the upper knife 2 and the upper knife base 22 to be constantly maintained. It is urged to move to the left (forward direction).

In the thread cutting device having the lower knife driving mechanism and the upper knife linking moving mechanism having the above-described structure, the lower knife table stopper (17) fixed to the lower knife table guide (lower knife table guide member) 16 is used to project the projecting piece. In the position following 17a, FIG.
As clearly shown in FIG. 5, a leaf spring 30 having a guide surface 29 inclined so that the distance from the straight line path in the direction B orthogonal to the sewing advancing direction A gradually increases toward the forward position is fixedly connected. . As shown in FIG. 8, the right end of one side edge 15e of the right long hole 15l of the left and right long holes 15r and 15l formed in the lower knife table 15 is fitted into the long hole 15l. A relief notch 31 is provided to add play to the movement (sliding contact) of the flanged pin 26l,
By the notch portion 31 and the inclined guide surface 29 of the leaf spring 30, the lower knife 1 alone moves from the middle position p1 to the forward position p2 after the upper knife 2 stops moving at the middle position p1 before the forward position p2. As shown by the solid line in FIG. 9, the movement locus of the most distal end portion 1c when moving in a line is gradually moved to the rear side in the sewing advancing direction A with respect to the straight path in the direction orthogonal to the sewing advancing direction A, and the lower knife 1 is gradually separated. A movement locus changing means for guiding the forward movement of the is configured.

The inclined guide surface 29 has a distance d of 0.5 to 0.5 between the most distal end portion 1c of the lower knife 1 and the straight path when the lower knife 1 moves forward to the forward position p2. 3m
The slope is formed so as to be set in the range of m, preferably 1.0 to 2.0 mm. The end portion 30a of the leaf spring 30 following the inclined guide surface 30 is curved toward the front side in the sewing advancing direction A so that the tip end thereof is farther from the lower knife 1. This is because when the lower knife 1 and the upper knife 2 return to the standby position after the thread cutting is completed, the lower knife 1
The purpose of this is to prevent the looper thread end portion sandwiched and held by the thread clamping spring 4 from entering the inside of the leaf spring 30, and the leaf spring 30 having such a curved end portion 30a.
Instead of this, a leaf spring 30 as shown in FIG. 10 may be used.

Next, the operation of the thread cutting device of the sewing machine having the above structure will be described. (1) Until the predetermined sewing operation by the sewing machine is completed, the lower knife 1 and the upper knife 2 have the thread catching portions 1a and 1b at the tip of the lower knife 1 on the side of the operation path of the looper 3 as shown in FIG. It was retracted to the right and was moved to the right in the direction B orthogonal to the sewing advancing direction A from the center of the needle bar to the right so that a distance d1 was secured between the most distal end 1c of the lower knife 1 and the center of the needle bar. It is in the standby position.

(2) After the sewing operation is completed, the drive lever 14 is driven to swing in the direction of the arrow X, and the lower knife base 15 and the lower knife 1 are moved to the left (forward position p2 as the drive lever 14 swings).
In the same direction), and following this, the upper knife table 22 receives the elastic force of the spring 28 and moves in the same direction. At this time, the lower knife table 15 and the upper knife table 22 are provided with the flanged pins 26r, 26l rotatably inserted and held at the free ends of the left and right knife guide lever links 24r, 24l on the lower knife table 15. In order to receive the guiding action of linearly slidingly moving in the left and right long holes 15r and 151, it moves to the left from the standby position toward the forward position p2 while drawing an inclined locus as shown by the solid line in FIG. The line is moved, and as shown in FIG. 3, the distance d2 between the tip portion 1c of the lower knife 1 and the center of the needle bar.
Is smaller than the distance d1 when the vehicle is in the standby position (d
When 2 <d1), that is, at the midway position p1 of the forward movement of the lower knife 1 and the lower knife table 15, the engaging projection 22a of the upper knife table 22 engages with the upper knife table stopper 23 and becomes the upper knife. Two
The movement of the upper knife table 22 is stopped, and both the lower knife 1 and the upper knife 2 reach substantially directly above the operation path of the looper 3.

(3) Only the lower knife base 15 and the lower knife 1 continue to move leftward from the midway position p1 as the drive lever 14 is driven and swung in the X direction. At this time, as shown in FIG. 4, the protruding portion 15c of the lower knife table 15 is brought into sliding contact with or moves closer to the protruding piece 17a of the lower knife table stopper 17, whereby the lower knife table 15 is sewn. The lower knife 1 is linearly moved and guided toward the forward movement position p2 without swinging to the front side in the traveling direction A. As shown in FIG.
The yarn catching portion 1b on the front end side passes in front of the looper yarn LY that is slantingly stretched between the cloth W and the front end of the looper 3 while being rushed into YL.

(4) When the lower knife table 15 and the lower knife 1 are further moved to the left, the projection 15c of the lower knife table 15 moves to the side of the inclined guide surface 29 of the leaf spring 30, and this inclined guide is formed. The flanged pin 26l, which is guided along the surface 29, fits into the long hole 15l and is in sliding contact with the one side edge 15e of the long hole 15l, enters the escape notch 31 and is loose. In order to be slidably guided in the state, the distal end portion 1c of the lower knife 1 is, as shown by the solid line in FIG. 9, located on the rear side in the sewing advancing direction A with respect to the straight path in the direction orthogonal to the sewing advancing direction A. The maximum forward movement position p2 shown in FIGS. 5 and 6 is reached while drawing a moving trajectory that gradually separates. When the maximum forward position p2 is reached, 0.5 to 0.5 is provided between the most distal end portion 1c of the lower knife 1 and the linear path in the direction orthogonal to the sewing advancing direction A.
A distance d of 3 mm, preferably 1.0-2.0 mm is ensured.

(5) Then, as the drive lever 14 is driven to swing in the X1 direction, the lower knife 1 returns (reverses) from the forward position p2 toward the midway position p1 as clearly shown in FIG. 12, and at the time of its return movement, as shown in FIG. 12, the needle catching NY and the looper thread L are made at the thread catching portions 1a and 1b.
Hook (capture) Y. Forward position p of this lower knife 1
At the time of return movement from 2 to the midway position p1, the most distal end portion 1c of the lower knife 1 is displaced to the rear side in the sewing advancing direction A with respect to the locus during forward movement, as shown by the dotted line in FIG. It will move back to a state that draws a linear trajectory,
As a result, the thread catching portions 1a and 1b at the tip of the lower knife 1 return and move through the position on the rear side in the sewing advancing direction with respect to the straight line path, and the thread catching range becomes wider in the sewing advancing direction.

Therefore, the needle thread NY and the looper thread LY to be captured and cut are formed at the time of the coarse stitching in which the stitch pitch is coarse so that the needle thread NY and the looper thread LY shift to the rear side in the sewing progress direction A, or in the form shown in FIG. As shown in FIG. 12, the yarn catcher 1
1 and 1b, the needle thread NY and the looper thread LY or the empty ring K are reliably captured without any mistake and pulled out to the side,
As shown in FIG. 3, it is possible to reliably cut the yarns NY, LY or the empty ring K by the sliding action of the blade edge 2a of the upper knife 2 and the catching portions 1a, 1b of the lower knife 1.

(6) Of the cut end portions of the cut needle thread NY and looper thread LY, the cut end portion connected to the looper 3 is sandwiched and held between the lower knife 1 and the thread clamp spring 4, and the next After being prepared for sewing, the upper knife 2 and the lower knife 1 together with the protrusion 15b and the engaging protrusion 22b draw an inclined locus as shown by the dotted line in FIG.
It returns to the standby position as shown in.

As in the above embodiment, the inclined guide surface 29 formed on the lower knife base stopper 17 is provided with the leaf spring 3.
By configuring from 0, while elastically absorbing and mitigating the impact when the lower knife table 15 moving at a relatively high speed collides with the inclined guide surface 29 and the mechanical vibration during the sliding contact guide, The lower knife base 15 can be moved and guided in the tilt direction to change the predetermined trajectory smoothly and securely without shock, and the lower knife can be adjusted to the stitch pitch and the like simply by selecting the spring constant of the leaf spring 30. The leading edge movement locus can be adjusted appropriately and arbitrarily to make the yarn catching performance more reliable. However, instead of the leaf spring 30, a rigid member that does not elastically deform is used for fixed sliding contact guide. The surface may be formed.

[0030]

As described above, according to the present invention, it is possible to move the lower knife, which has moved forward together with the upper knife to the midway position, to the forward movement independently from the midway position to the forward movement position of the forward movement range. As the tip movement locus is inclined toward the rear side in the sewing advancing direction with respect to the linear path in the direction orthogonal to the sewing advancing direction as the tip moving path approaches the advancing position, the lower knife that has moved to the advancing position is moved to the middle position. When moving back to
It is possible to return and move the thread catching portion at the tip through the position on the rear side in the sewing traveling direction with respect to the straight line path,
It is possible to widen the thread catching range in the sewing advancing direction by making a very simple structure improvement that only changes the trailing movement path of the lower knife without major modification of the basic structure. Therefore, when the needle thread and the looper thread to be captured and cut are shifted to the rear side in the sewing progress direction and the stitch pitch is coarse,
Alternatively, even when the empty ring as described above is to be cut, the needle thread and the looper thread or the empty ring are reliably caught by the thread catching portion without fail to ensure the predetermined thread cutting function. There is an effect that it can be exhibited.

In particular, as described in claim 3, the guide surface for guiding the forward movement of the lower knife in the inclination direction is composed of the leaf spring, so that the predetermined movement locus can be smoothly and surely changed without shock. By selecting the spring constant of the leaf spring, it is possible to properly and arbitrarily adjust the locus of movement of the lower knife leading edge in accordance with the stitch pitch or the like to further secure the thread catching performance.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a thread cutting device for a sewing machine according to the present invention.

FIG. 2 is a plan view showing a state in which the yarn cutting device is in a standby position.

FIG. 3 is a plan view showing a state in which the yarn cutting device has moved forward to an intermediate position.

FIG. 4 is a plan view showing a state when the yarn cutting device moves forward from a midway position to a forward movement position.

FIG. 5 is a plan view showing a state when the yarn cutting device has moved forward to the most advanced position.

FIG. 6 is a front view of FIG.

FIG. 7 is an enlarged perspective view showing a configuration example of a main part of the yarn cutting device.

FIG. 8 is an enlarged plan view showing a configuration example of a main part of the yarn cutting device.

FIG. 9 is an explanatory diagram of a locus of movement of the lowermost edge of the lower knife in the yarn cutting device.

FIG. 10 is an enlarged perspective view showing another configuration of a main part of the yarn cutting device.

FIG. 11 is a perspective view of an essential part showing a first operation state of a thread cutting operation by a thread cutting device of a general sewing machine.

FIG. 12 is a perspective view of essential parts showing a second operation state of the thread cutting operation by the thread cutting device of the same general sewing machine.

FIG. 13 is a perspective view of essential parts showing a third operation state of the thread cutting operation by the thread cutting device of the same general sewing machine.

FIG. 14 is a perspective view of an essential part showing a state in which the lower knife has entered the needle thread loop in the thread cutting operation by the thread cutting device of the same general sewing machine.

FIG. 15 is a perspective view of an essential part showing a state where the lower knife has started the return movement in the thread cutting operation by the thread cutting device of the same general sewing machine.

FIG. 16 is an explanatory diagram of the locus of movement of the lower knife leading edge portion in the thread cutting device of the conventional sewing machine.

FIG. 17 is a vertical cross-sectional side view of an essential part for explaining the situation of the needle thread when the material is sewn with a coarse stitch pitch.

FIG. 18 is a vertical cross-sectional side view of a main part for explaining the situation of the needle thread when the empty ring is the cutting target.

[Explanation of symbols]

1 lower knife (first knife) 1a, 1b Thread catching section 1c cutting edge 2 Upper knife (2nd knife) 3 looper 12 Female mounting plate 14 Drive lever 15 Lower knife stand 15r, 15l long hole 16 Lower knife table guide (lower knife table guide member) 17 Lower knife stand stopper 22 Upper knife stand 24r, 24l Female guide lever link 29 Inclined guide surface 30 leaf spring A sewing direction B Direction orthogonal to the sewing advancing direction NY needle thread LY looper thread d Distance between the tip of the lower knife and the straight path

Claims (5)

[Claims] 1. A first knife having a thread catching portion for hooking a needle thread and a looper thread at its tip, a second knife cutting the thread caught by the thread catching portion of the first knife, and the first knife. The knife is reciprocally driven in the direction orthogonal to the sewing advancing direction between the standby position in which the thread catching portion at the tip of the knife is retracted to the side of the looper operation path and the forward position in which the needle thread loop is projected. A drive lever that is reciprocally swingably mounted on the female mounting portion, and the first lever is linked to the reciprocating swing of the drive lever.
In a thread cutting device of a sewing machine, which comprises a mechanism for reciprocating the second knife following the first knife when the knife reciprocates to a midway position before the standby position and the forward position, the first knife is When moving forward from the midway position to the forward position along the straight line path in the direction orthogonal to the sewing traveling direction, the closer to the forward position, the trailing edge of the trailing edge of the linear path gradually deviates to the rear side in the sewing moving direction. So first
A thread cutting device for a sewing machine, which is provided with a moving locus changing means for guiding the forward movement of the knife. 2. A notch in a part of one edge of a long hole formed in the first knife table so as to guide the reciprocating movement of the first knife between the standby position and the forward position. Is formed, and the first knife base guide member fixed to the knife mounting portion is configured to guide the outward movement of only the first knife after the second knife is stopped at the midway position. A guide surface is formed so that the distance from the straight line path in the direction orthogonal to the sewing advancing direction gradually increases toward the forward movement position, and the inclined guide surface and a part of the long hole edge are formed. The thread cutting device for a sewing machine according to claim 1, wherein the movement locus changing means is constituted by a notch. 3. The thread cutting device for a sewing machine according to claim 2, wherein the inclined guide surface formed on the first knife table guide member is composed of a leaf spring. 4. A mechanism for reciprocally moving the first knife between a standby position and a forward position in association with the reciprocating swing of the drive lever is provided on both sides in the reciprocating direction with the point of linkage with the drive lever interposed therebetween. 4. The thread cutting device for a sewing machine according to claim 1, comprising a knife guide lever link arranged and a spring provided so as to urge the second knife to move in the forward direction. 5. The distance between the most distal end of the first knife and the linear path when the first knife moves forward to the forward position is set in the range of 0.5 to 3 mm. The thread cutting device for a sewing machine according to any one of claims 1 to 4.