CN107532358B - Double-thread lockstitch sewing machine with anti-thread mark opening device - Google Patents

Abstract

The invention provides a double-thread lockstitch sewing machine with a thread-opening preventing device, which is used for preventing the thread-opening of a self-thread winding ring and is also provided with a looper thread pulling-back force applying device. The looper thread pulling-back force applying device hooks a looper thread portion hung between the looper thread supply source device and the looper and moves the looper thread portion to the side during the forward movement of the looper after the thread looping, thereby bending the looper thread portion and applying a pulling-back force toward the looper thread supply source device to the looper thread portion supplied to the looper. Therefore, according to the double-thread lockstitch sewing machine with the anti-stitch-breakage device of the present invention, it is possible to obtain the anti-stitch-breakage effect of the thread loop, and to perform the next sewing reliably and with good appearance without causing the trouble of the cutting process of the looper thread after the thread loop and the holding of the looper thread after the cutting.

Description

Double-thread lockstitch sewing machine with anti-thread mark opening device

Technical Field

The invention relates to a double-thread lockstitch sewing machine with a thread-opening preventing device, which mainly uses a double-thread lockstitch sewing machine represented by a transverse cylinder shape, forms a stitch of a double-thread lockstitch through a machine needle thread and a looper thread, and can prevent the thread from being opened at the sewing finishing part of the stitch of the double-thread lockstitch.

Background

In order to prevent the unique opening of the stitches formed by the double lockstitch sewing machine as described above, the present applicant has succeeded in developing a double lockstitch sewing machine with an opening prevention device disclosed in japanese patent application laid-open nos. 2011-206527 and 2013-6009 (hereinafter, referred to as the prior art of the present applicant).

As shown in fig. 28 and 29, the anti-ravel device of the double-lock stitch sewing machine according to the related art of the present applicant includes: needles 2a and 2b that hold the needle threads 20a and 20b (see fig. 17 to 23 described in the embodiment of the present invention) and move up and down with respect to a needle drop position A, A set at a distance in the left-right direction at substantially the center of the needle plate 12 (see fig. 17 to 23 described in the embodiment of the present invention); a looper 1 which can hold a looper thread 10 and advance and retreat in the arrangement direction of the needle drop position A, A, and which grips needle thread loops 20a2 and 20b2 formed below a needle plate 12 when advancing (see fig. 17 to 23 described in the embodiment of the present invention); a thread hooking hook 3 which is curved in an arc shape and can move closer to or away from the looper 1, and which swings within a plane substantially parallel to the needle plate 12 about a vertical fulcrum shaft 30 between a waiting position away from the looper 1 shown in fig. 28 and a thread hooking position closer to the looper 1 shown in fig. 29; a looper thread holder 6 which is curved in an arc shape, is fixed to the upper surface of the midway portion of the thread hanging hook 3 by a fixing screw 60, and swings integrally with the thread hanging hook 3; a thread operating cylinder 32 for driving the thread hook 3 and the looper thread holder 6 to swing between the waiting position and the thread hanging position; a swing lever 9 and a stopper lever 4 which are disposed at a position farther from the needle plate 12 than the thread hooking hook 3, supported by the upper surface of the needle plate table 11, and swing about a vertical pivot shaft 90 in a plane substantially parallel to the needle plate 12 so that the needle loops 20a2 and 20b2 caught by the thread hooking hook 3 at the thread hooking position are held at a holding position between the thread hooking position and the waiting position; a stopper cylinder 42 that drives the stopper rod 4 to swing from an engagement position where the stopper rod is engaged with a part of the swing lever 9 to a retreat position where the stopper rod is disengaged from the engagement position; a link lever 35 which links the hook 3 and the swing lever 9; a return spring 91 disposed between the tie rod 35 and a spring hook portion 95 projecting forward on the left side of the wire operating cylinder 32; and a control unit 8 for selectively controlling the operation of the thread operating cylinder 32 and the stopper cylinder 42 after normal sewing is completed, so that one needle thread loop 20b2 caught by the hook portion 3b at the tip end of the thread hook 3 at the thread hanging position is held at the holding position, and the thread holder portion 6a at the tip end of the looper thread holder 6 is positioned above the looper 1 in front of the hook portion 3b, and at least one needle sewing operation is performed while maintaining this state (see fig. 15 explained in the embodiment of the present invention).

In addition, in the thread breakage preventing device of the double-lock stitch sewing machine of the related art of the present applicant, the needle plate table 11 is configured as an integral structure that is long in the left-right direction, but in the embodiment of the present invention, a structure in which the needle plate table 11 is divided into two parts in the left-right direction will be described. In addition, the same or corresponding components and constituent parts as those of the thread breakage preventing device of the double-lock stitch sewing machine described in the embodiment of the present invention will be denoted by the same reference numerals as those described in the thread breakage preventing device of the embodiment of the present invention, and the detailed description thereof will be omitted.

According to the above-described conventional thread breakage preventing device of the applicant, after the normal sewing is completed, the control unit 8 controls the operations of the hook 3, the looper thread holder 6, the stopper rod 4, and the swing lever 9 to perform the sewing operation of one needle as described above, so that the looper thread 10 passes through the final needle thread loop 20b2 formed on the right side (left side in fig. 30) of the back surface of the sewing fabric at the end of the stitch M of the double lock stitch, is folded back in front of the needle thread 20b drawn out to the back surface side of the sewing fabric at the time of one needle for preventing the thread breakage as shown in fig. 30, and is cut at a position passing through the right final needle thread loop 20b2, and as a result, another thread loop in a knotted shape as shown in the drawing is formed by the needle thread 20b and the looper thread 10. On the other hand, the left-hand (right-hand in fig. 30) needle thread 20a drawn out from the back side of the sewing fabric at the time of one-needle sewing passes through the final needle thread loop 20a2 formed last at the back side of the sewing fabric at the time of normal sewing, and the final needle thread loop 20a2 is looped by itself. Thus, by the synergistic action of the left self-looper portion and the right knotted other-thread looper, the specific opening of the stitch M of the double lock stitch can be prevented regardless of the direction from which the force acts on the looper thread 10.

Documents of the prior art

Patent document 1: japanese patent laid-open publication No. 2011-

Patent document 2: japanese patent laid-open publication No. 2013-6009

Disclosure of Invention

As described above, according to the related art double-lock stitch sewing machine with an anti-ravel device of the present applicant, by continuously performing the sewing operation of one stitch for preventing the ravel described above after the normal sewing is completed, it is possible to effectively prevent the occurrence of the peculiar ravel in the stitches of the double-lock stitch. Therefore, after the sewing is finished, it is not necessary to perform other work dedicated to thread-opening prevention such as knotting, and the sewing work efficiency can be improved when a large number of sewn products are continuously produced one by one. However, in the double-lock stitch sewing machine which has been successfully developed by the applicant of the present invention, the looper thread may be loosened by the thread open preventing operation for performing the thread open preventing operation from the thread loop by adjusting the type of the thread and the tightness of the thread. As a result, the following problems occur: when sewing is finished, the looper thread is cut by the thread cutting device and the end of the looper thread after cutting is held badly, so that the next sewing process can not be performed as required. This problem will be described in detail below.

In the double-lock-stitch sewing machine of the related art by the applicant of the present invention, in order to obtain the thread unraveling prevention effect from the thread looper, the following operations as described in fig. 18 and 19 of the embodiment of the present invention are indispensable: after normal sewing is completed, the hook 3 is moved closer to the looper 1, the needle thread loop 20a2 is held at a position closer to the forward end side of the looper 1 than the needle lowering position, the looper thread holder 6 is moved closer to the looper 1, and the looper thread 10 extending from the sewing fabric is held at the needle falling position on the left side by the looper thread holder 6a at the tip of the looper thread holder 6. The slackening of the looper thread 10 caused by such an operation essential for obtaining the thread unraveling prevention effect from the thread looping ring may not be removed by adjusting the type of thread, the thread tightness, or the like as described above.

As shown in fig. 31, if the looper thread 10 slackens, when the needle threads 20a and 20b located on the rear side (near side in fig. 31) of the looper 1 move downward as indicated by an arrow d as the needle moves upward, the looper thread 10 slides in contact with the needle threads 20a and 20b and is caught under the looper 1. In such a state, even if the thread cutting device 5 is operated to advance the movable knife 50 in the arrow x direction from the forward position close to the left front of the looper 1 to the outer position on the other side (left side) close to the needle drop position as shown in fig. 32, the looper thread catching portion 50a on the tip side of the movable knife 50 cannot smoothly catch the looper thread 10 caught between the vicinity of the tip of the looper 1 and the back side of the sewing fabric W, and the looper thread 20a and the looper thread 20b are caught by the needle thread catching portion 50b of the movable knife 50 and cut. The cut machine needle threads 20a and 20b are normally moved upward of the needle plate 12 by a machine needle thread moving mechanism or the like, and the cut looper thread 10 is in a free state with respect to the thread hole at the tip of the looper 1.

As a result, the following problems occur: in the next sewing, the looper thread 10 is separated from the top thread hole of the looper 1 depending on the length of the looper thread 10 remaining in the top thread hole of the looper 1, and a stitch is not formed, or even if a stitch can be formed, a long looper thread 10 remains in the sewing start portion, and thus the finish of the sewing object and the appearance are deteriorated.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a double-thread lockstitch sewing machine with a thread breakage preventing device, which can obtain a thread breakage preventing effect from a thread winding loop, and can perform next sewing reliably and with good appearance without causing a failure in cutting processing of a looper thread after the thread winding loop and holding of the looper thread after the cutting.

In order to achieve the above object, the present invention relates to a double lockstitch sewing machine with an anti-raveling apparatus, the double lockstitch sewing machine comprising: a needle which holds a needle thread and moves in the vertical direction; and a looper which can hold a looper thread and perform a retracting operation in a direction substantially orthogonal to an up-and-down moving path of the needle, and grasp a needle loop formed below a needle plate by the needle at the time of the advancing operation, wherein the looper held by the looper performs other-thread looping on the needle loop grasped by the advancing operation of the looper, thereby forming a double-lock stitch on a sewn fabric, the stitch open preventing device comprising: a needle thread holding mechanism capable of moving closer to or away from the looper, the needle thread holding mechanism holding a needle thread loop caught by the looper at a position closer to a forward end side of the looper than a descending position of the needle during the approaching movement; a looper thread holding mechanism which can perform an operation of moving closer to or away from the looper and which holds a looper thread extending from the looper to a sewing fabric at a position forward or backward of a lowering position of the needle at the time of the approaching operation; and a control unit that controls a contact and separation operation of the needle thread holding mechanism and the looper thread holding mechanism in association with an operation of the needle and the looper and a feeding operation of the sewing fabric, wherein after normal sewing is finished with the looper at an advanced position and the needle at a raised position, the control unit causes the needle thread holding mechanism and the looper thread holding mechanism to perform a close operation to hold the needle thread loop at a position closer to an advanced end side of the looper than a lowered position of the needle and to hold the looper thread at a position closer to a front side or a rear side than the lowered position of the needle, maintains the state until the needle passes through the needle thread loop caught by the looper and then descends, and releases the position holding of the needle thread loop, and the control unit controls the contact and separation operation of the needle thread holding mechanism and the looper thread holding mechanism in association with the operation of the needle and the feeding operation of the sewing fabric, and causes the looper to be positioned closer to the front side or rear side than the, The double lock stitch sewing machine with a stitch open preventing device includes:

and a looper thread pulling-back force applying device configured to hook and move a looper thread portion hooked between the looper thread supply source device and the looper to a lateral direction during an advancing operation of the looper after the thread looping, thereby bending the looper thread portion and applying a pulling-back force toward the looper thread supply source device to the looper thread portion supplied to the looper.

At least two looper thread guides for guiding a looper thread portion hung between the looper thread supply source device and the looper to move substantially linearly are provided between the looper thread supply source device and the looper,

the looper thread pulling-back force applying device includes:

a swing arm capable of swinging back and forth between a position facing the looper thread guide and a lateral position where the looper thread is partially bent in a horizontal or substantially horizontal plane with a position close to the looper thread supply source device as a fulcrum shaft;

a looper thread hooking portion attached to a distal end portion of the swing arm and capable of hooking a looper thread portion of a looper thread guide on a side closer to the looper thread supply source device out of the two looper thread guides; and

an actuator that drives the swing arm to swing reciprocally between the two positions.

Effects of the invention

According to the double-thread lockstitch sewing machine with the thread breakage preventing device of the present invention having the above-described configuration, after the normal sewing is finished with the looper in the forward state, the needle loop caught by the looper is held at the position closer to the forward end side of the looper than the descending position of the needle, and the looper thread is held at the position closer to the front side or the rear side than the descending position of the needle, the state is maintained until the needle passes through the needle loop caught by the looper and descends, then the position holding of the needle loop is released, and the sewing operation of at least one needle including the operation of descending the needle after passing through the needle loop is executed, whereby the former needle loop is self-looped by the needle held by the descending needle, and the looper thread is pressed by the self-looped portion, whereby the looper thread is pressed irrespective of the magnitude of the tension applied to the needle thread and the looper thread, the separation of the looper thread can be prevented, and the opening of the stitches can be prevented even if other special process operations for preventing the opening of the stitches such as knotting are performed.

Further, in the forward movement of the looper after the thread open prevention operation of the thread loop, the looper thread portion hooked between the looper thread supply source device and the looper is hooked and bent to move laterally in accordance with the operation of the looper thread pulling-back force applying device, and the pulling-back force toward the looper thread supply source device is applied to the looper thread portion, whereby the looper thread is held at a position on the front side or the rear side of the lowered position of the machine needle after the normal sewing is completed, and the slackening of the looper thread caused by the indispensable operation for realizing the thread open prevention function of the thread loop can be eliminated. Thus, the cutting failure due to the slackening of the looper thread after the thread is looped around and the failure in holding the looper thread after the cutting can be eliminated, and the next sewing can be performed reliably and with good appearance as prescribed.

In the double-lockstitch sewing machine with an anti-running out apparatus according to the present invention, it is preferable that at least two looper thread guides for guiding a looper thread portion hung between the looper thread supply source apparatus and the looper to move substantially linearly are provided between the looper thread supply source apparatus and the looper, and the looper thread pulling-back force applying apparatus includes: a swing arm which is capable of reciprocating swing between a position facing the looper thread guide and a lateral position where the looper thread portion is bent in a horizontal or substantially horizontal plane, with a position close to the looper thread supply source device as a fulcrum shaft; a looper thread hooking portion which is attached to a distal end portion of the swing arm and which is capable of hooking a looper thread portion of a looper thread guide on a side closer to the looper thread supply source device out of the two looper thread guides; and an actuator for driving the swing arm to perform reciprocating swing between the two positions.

Further, since the looper thread pulling-back force applying device is constituted by a swing arm which is reciprocally swung in a horizontal or substantially horizontal plane about a fulcrum shaft and an actuator which drives the swing arm to reciprocally swing between two positions, the mechanism is relatively simple and can be compactly stored in a small horizontal space in the base part of the sewing machine. Further, according to the positional relationship between the two looper thread guides and the swing arm, the looper thread portion is pulled linearly in the front-rear direction on the side close to the looper thread supply source device and is pulled obliquely in the front-rear left-right direction on the side close to the looper, whereby the effect of being able to apply a pull-back force to the looper thread by a small amount of swing of the swing arm sufficient to eliminate the slack thereof is also achieved.

In particular, the actuator of the looper thread pulling-back device is preferably constituted by a combination of: a spring for biasing the swing arm to swing forward from a position facing the looper thread guide to the lateral position; and a fluid pressure cylinder that drives the swing arm to swing back from the side position to a position facing the looper thread guide against the biasing force of the spring.

In this case, the elastic force of the spring can be effectively utilized to apply an appropriate looper thread retracting force according to the degree of slackening of the looper thread, and it is possible to prevent an abnormal retracting force (tension) from acting on the looper thread or to prevent a cutting failure and a failure in holding the looper thread after cutting due to an insufficient retracting force.

In the double-lock stitch sewing machine with an anti-thread-unraveling device according to the present invention, it is preferable that the control unit is configured to: the sewing operation of at least one stitch for the self-looper is performed when the feeding of the sewing fabric is stopped or the feeding operation is performed with a smaller feed amount than that in normal sewing.

In this case, the pressing force of the looper thread by the self-looper portion can be increased by making the self-looper portion compact, and the withdrawal of the looper thread at the sewing completion portion and the thread unraveling prevention effect by the withdrawal can be further secured.

In the double-thread lockstitch sewing machine with an anti-running out apparatus according to the present invention, it is preferable that the looper thread holding body is configured to be capable of moving closer to or away from the looper integrally with the looper thread holding mechanism.

In this case, the drive mechanism of the needle thread holding mechanism can be used as the drive mechanism of the looper holding mechanism, and the structure of the thread separation preventing device body can be made as small and simple as possible, and the cost can be reduced.

The double-thread lockstitch sewing machine according to the present invention is applied to a horizontal tubular double-thread lockstitch sewing machine, but a needle double-thread lockstitch sewing machine other than the horizontal tubular sewing machine or a flat bed double-thread lockstitch sewing machine may be used as the target sewing machine.

Drawings

Fig. 1 is an external perspective view showing the entire horizontal tubular double-thread lockstitch sewing machine according to the embodiment of the present invention in a state where an upper cover of a base part of the sewing machine is removed.

Fig. 2 is an enlarged perspective view of a main portion of fig. 1.

Fig. 3 is a perspective view showing a main part structure of the stitch open preventing device of the transverse tubular double-lock stitch sewing machine.

Fig. 4 is a perspective view showing a state where a part of the configuration of the main part of the trace disconnection preventing apparatus is removed.

Fig. 5 is a plan view showing a main part structure of the trace disconnection preventing device.

Fig. 6 is a bottom view for explaining the configuration and the main part of the first operation of the stopper mechanism of the trace disconnection preventing device.

Fig. 7 is a bottom view of the main part for explaining the structure and the second operation of the stopper mechanism.

Fig. 8 is a bottom view of the main part for explaining the structure and the third operation of the stopper mechanism.

Fig. 9 is a bottom view of the essential parts for explaining the structure of the stopper mechanism and the fourth operation.

Fig. 10 is an exploded perspective view for explaining the structure of the reciprocating drive moving mechanism of the thread cutting device of the horizontal tubular double-thread lockstitch sewing machine.

Fig. 11 shows a state where the thread cutting device is retracted to the retracted position by the reciprocating drive movement mechanism, where (a) is a plan view of a main portion and (B) is a longitudinal sectional view along line a-a of fig. 11 (a).

Fig. 12 is an explanatory diagram showing a first thread breakage preventing operation of the thread breakage preventing device in a state where the thread cutting device is advanced to the advanced position by the reciprocating drive moving mechanism.

Fig. 13 is an enlarged plan view of a main part showing the structure of the looper thread pulling-back force applying device according to the embodiment of the present invention and a state in normal sewing.

Fig. 14 is an enlarged plan view showing a configuration of a looper thread pulling-back force applying device according to an embodiment of the present invention and a main part of a looper thread pulling-back operation state.

Fig. 15 is a block diagram showing a configuration of a control system of the horizontal tubular double-lock stitch sewing machine according to the first embodiment including the anti-stitch-off device.

Fig. 16 is a time chart showing the operation contents of the control unit for preventing the stitches from being opened in time series.

Fig. 17 is an explanatory diagram of a first disconnection preventing operation of the above-described disconnection preventing device.

Fig. 18 is an explanatory diagram of a second disconnection preventing operation of the above-described disconnection preventing device.

Fig. 19 is an enlarged perspective view of a main part of the operating state of fig. 18, viewed from a direction opposite to that of fig. 18.

Fig. 20 is an explanatory diagram of a third open prevention operation of the trace open prevention device.

Fig. 21 is an explanatory diagram of a fourth disconnection preventing operation of the above-described disconnection preventing device.

Fig. 22 is an explanatory diagram of a fifth disconnection preventing operation of the above-described disconnection preventing device.

Fig. 23(a) to (f) are perspective views sequentially explaining a main part of the thread cutting operation of the thread cutting device.

Fig. 24 is an enlarged perspective view of a main part of the state of fig. 23(a) viewed from the opposite direction to fig. 23.

Fig. 25 is an enlarged perspective view of a main part of the state of fig. 23(c) as viewed from the opposite direction to fig. 23.

Fig. 26 is a view of the double-thread lockstitch structure of the horizontal tubular double-thread lockstitch sewing machine according to the embodiment of the present invention, as viewed from the back surface of the sewn fabric.

Fig. 27 is a bottom view schematically showing a stitch structure of a sewing end portion of a conventional double-thread lock stitch.

Fig. 28 is a plan view schematically showing the structure of the main part of a prior art anti-stitch wiring device of the applicant.

Fig. 29 is a plan view for explaining an operation state of a main part of a related art anti-stitch wiring device of the applicant.

Fig. 30 is a view of a double lock stitch structure obtained by a prior art anti-stitch opening device of the present applicant as viewed from the back of a sewn fabric.

Fig. 31 is an enlarged perspective view of a main part of a state corresponding to fig. 24, which is a prior art of the present applicant.

Fig. 32 is an enlarged perspective view of a main part of a state corresponding to fig. 25, which is a prior art of the present applicant.

Description of the reference numerals

1 curved needle

2a, 2b machine needle

3 hook for hanging wire

4 position limiting component

6 looper thread holder

8 control part

10 looper thread

10a looper thread part

12 needle board

20a, 20b machine needle and thread

20a1, 20b1 needle thread part

20a2, 20b2 needle thread ring

84 looper thread pulling-back force applying device

150. 150a, 150b looper thread guide

151 fulcrum shaft

152 swing arm

153 actuator

153a spring

153b telescopic fluid pressure cylinder

154 looper thread hooking part

A needle falling position

B base of sewing machine

M double-thread lock-sewn stitch

H-shaped anti-opening device

W sewing fabric

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, the same components as those of the conventional double-lock-stitch sewing machine of the applicant are denoted by the same reference numerals.

Fig. 1 is an external perspective view showing an entire horizontal tubular double-lock stitch sewing machine according to an embodiment of the present invention with an upper cover of a base part of the sewing machine removed, fig. 2 is an enlarged perspective view of a main part of fig. 1, fig. 3 and 4 are perspective views showing a main part structure of a stitch open preventing device provided in the horizontal tubular double-lock stitch sewing machine, fig. 5 is a plan view showing the main part structure of the stitch open preventing device, and fig. 6 to 9 are bottom views for explaining a structure of a stopper mechanism of the stitch open preventing device and main parts of first to fourth operations.

Fig. 10 is an exploded perspective view for explaining the structure of the reciprocating drive moving mechanism of the thread cutting device of the horizontal tubular double-thread lockstitch sewing machine, fig. 11 shows a state where the thread cutting device is retracted to the retracted position by the reciprocating drive moving mechanism, where (a) is a plan view of a main portion, (B) is a longitudinal sectional view along the line a-a in fig. 11(a), fig. 12 is a state where the thread cutting device is advanced to the advanced position by the reciprocating drive moving mechanism and the movable cutter is advanced to the leftmost side, where (a) is a plan view of a main portion, and (B) is a longitudinal sectional view along the line B-B in fig. 12 (a).

In the following description, expressions made of "left and right" and "front and rear" indicated by arrows and characters are used in fig. 3 to 5 and fig. 10 to 12. Here, "front" means a side close to a sewing worker, "rear" means a side far from the sewing worker, and "left and right" are "left and right" when viewed from a front side close to the sewing worker.

As shown in fig. 1 and 2, in the horizontal tubular double-thread lockstitch sewing machine according to the present embodiment, the sewing machine arm C and the sewing machine bed B extend substantially parallel to each other from the upper and lower positions of the sewing machine body D toward the left side. A needle driving mechanism for reciprocating the left and right needles 2a and 2b in the vertical direction, a presser foot driving mechanism for reciprocating the presser foot in the vertical direction, a power transmission mechanism for transmitting power to the driving mechanisms, and the like are incorporated in the arm C of the sewing machine.

As shown in fig. 5, the horizontal tubular double-thread lockstitch sewing machine includes a looper 1, left and right needles 2a and 2B (see fig. 17 to 23), a needle plate 11 attached to the upper surface of a sewing machine bed B, a stitch open preventing device H provided on the needle plate 11, a needle plate 12 attached to the needle plate 11, and a looper thread pulling-back force applying device 84.

A looper 1, a reciprocating drive moving mechanism 70, and the like are incorporated in a sewing machine bed B at a lower portion of the needle plate 12, the looper 1 holding a looper thread 10 and moving back and forth in a left-right direction substantially orthogonal to a vertical reciprocating path of the needles 2a and 2B, the reciprocating drive moving mechanism 70 reciprocating-moving a thread cutting device 5 and a blade portion 51e of a fixed knife 51 of the thread cutting device 5 between an advance position P1 and a retreat position P2, and reciprocating-driving-moving only a movable knife 50 described later linearly in an x-y direction between an outer position on one side (right side) and an outer position on the other side (left side) of the needle fall position in a state where the thread cutting device 5 is moved to the advance position P1, wherein the advance position P1 is close to the needle plate 12 and the looper 1 and a contact member 34 and a stopper member 33 described later come into contact with each other as shown in fig. 11(a) and 11(B) As shown in fig. 12(a) and 12(B), the retracted position P2 is located to the right and to the rear of the advanced position P1.

The left and right needles 2a and 2b are attached to the lower end of a needle bar (not shown) that ascends and descends in conjunction with the rotation of a transmission rotary shaft (not shown) in the arm C of the sewing machine. A, A in fig. 3 and 5 indicates the needle drop position (lowered position) of the needles 2a and 2 b. The needle fall positions A, A are set at intervals in the left-right direction at substantially the center of the needle plate 12.

The looper 1 is disposed in the bed B of the sewing machine, and is moved forward and backward (left and right) in the arrangement direction of the needles 2a and 2B substantially orthogonal to the vertical reciprocating paths of the needles 2a and 2B by the operation of a looper driving mechanism (not shown). The solid line in fig. 5 indicates a state in which the looper 1 is operated at the left carry position, and the broken line in fig. 5 indicates a state in which the looper 1 is operated at the right retreat position. As shown by the solid line in fig. 5, the tip end portion of the looper 1 positioned at the left position extends in the left direction beyond the needle fall position A, A, and as shown by the broken line in fig. 5, the tip end portion of the looper 1 positioned at the right retreat position is disposed apart to the right of the needle fall position A, A.

The horizontal tubular double-thread lockstitch sewing machine performs sewing of a sewing material (not shown) placed on the needle plate 12 by the raising and lowering operation of the needles 2a and 2b and the left and right moving operation of the looper 1. The sewing material is pressed by the presser foot on the needle plate 12, and is transported and moved in the arrow Y direction of fig. 5 by the operation of the feed mechanism provided inside the sewing machine base B. The feeding mechanism includes feeding teeth which repeatedly perform the operation of projecting above the needle plate 12 to move backward and sinking below the needle plate 12 to move back forward, and the sewing fabric is intermittently conveyed and moved along the arrow Y direction by the feeding teeth.

The needle bar, the looper drive mechanism, and the feed mechanism are known mechanisms that operate in synchronization with each other by transmission from a transmission rotary shaft (not shown). The needles 2a and 2b pass through the sewing fabric while holding the needles 20a and 20b (see fig. 17 to 23), reach below the needle plate 12, and then rise to be drawn upward above the sewing fabric. The looper 1 holds the looper thread 10 (see fig. 17 to 23), advances to the left while the needles 2a and 2b start to rise, and catches the thread loops 20a2 and 20b2 of the needle threads 20a and 20b formed below the needle plate 12. The sewing fabric is transported and moved when the needles 2a and 2b are raised. The needles 2a and 2b descend so as to penetrate the fabric being conveyed and sewn, and pick the looper thread 10 held by the looper 1 that is moving backward. The double-thread lockstitch sewing machine repeats the above operations to form a stitch of the double-thread lockstitch on the sewn fabric.

Next, the stitch open preventing device H provided in the above-described horizontal tubular double-lock stitch sewing machine will be described in detail. The disconnection preventing device H includes a needle thread holding mechanism, a looper thread holding mechanism, a stopper mechanism, a link lever 35 as a connecting member for linking the hook 3 (described later) of the needle thread holding mechanism and the stopper member 4 (described later) of the stopper mechanism, and a control unit 8 (described later).

The needle thread holding mechanism includes a thread hooking hook 3 and a reciprocating thread operating cylinder 32, and the reciprocating thread operating cylinder 32 drives the thread hooking hook 3 to swing about a vertical support shaft 30 between a waiting position away from the looper 1 and a thread hooking position close to the looper 1. A support shaft 30 as a swing center of the hook 3 is disposed near a right rear side corner of the needle plate 12 and supported on the needle plate base 11.

The wire hook 3 has an arc-shaped curved shape, and is continuously provided at the distal end portion of the support arm 3e extending leftward from the support shaft 30 so as to be folded back forward. The tip end of the hook 3 is formed with a hook portion 3b projecting outward from the left rear surface toward the needle drop position A, A below the needle plate 12. The support arm 3e has an extension portion 3c extending forward from the support shaft 30, and a tip end portion of the extension portion 3c is connected to one end portion of the link 35.

As shown in fig. 5, a looper thread holding member 6 having an arc-shaped curved shape is fastened as a looper thread holding mechanism to the base of the thread hanging hook 3 by two fixing screws 60, 60. The distal end portion of the looper thread holding member 6 extends forward substantially along the left side of the thread hooking hook 3, and faces the needle falling position A, A at a position forward of the distal end portion of the thread hooking hook 30. A looper thread holder 6a is formed at the tip of the looper thread holder 6 so as to be bifurcated. The looper thread holder 6 is configured such that the position thereof with respect to the thread hooking hook 3 can be adjusted by loosening the fixing screws 60, and the looper thread 10 can be reliably held by the distal looper thread support portion 6a by this position adjustment.

As shown in fig. 6 to 9, the stopper mechanism includes: a stopper member 14 fixed to a distal end portion (left end portion) of the output rod 31 of the wire operating cylinder 32 by a stopper screw 36, and configured to drive the stopper member 14 to linearly reciprocate in the left-right direction by extending and contracting the wire operating cylinder 32 by the working gas supplied through the gas supply pipe 33; a swing lever 9 that can be engaged with or disengaged from a part of the stopper member 14; a spring 96 that is biased to swing in a direction in which the swing lever 9 engages with a part of the stopper member 14 to position the wire hook 3 at the waiting position; and a single-acting (push-out driving type toward the left) stopper cylinder 42 that forcibly releases the engagement between the swing lever 9 and a part of the stopper member 14 against the swing urging force of the spring 96.

The output rod 41 of the stopper cylinder 42 is configured such that the swing lever 9 swings counterclockwise against the swing urging force of the spring 96 as the stopper cylinder 42 is pushed and driven in the left direction by the working gas supplied through the air supply pipe 43.

The swing lever 9 is supported on the upper surface of a swing lever mounting base 92 so as to be swingable about a vertical support shaft 90. As shown in fig. 6, the swing lever 9 has an engagement claw 9a at a distal end portion thereof, which is engageable with a part of the stopper member 14, and when the stopper member 14 is moved in the left direction by the extending operation of the wire operating cylinder 32 (see fig. 4), that is, when the wire hook 3 is moved to the waiting position, the biasing force of the spring 96 causes the swing lever 9 to come into contact with the side portion of the stopper member 14, and when the stopper member 14 is moved in the right direction by the retracting operation of the wire operating cylinder 32, as shown in fig. 7, the biasing force of the spring 96 causes the swing lever 9 to swing clockwise about the support shaft 90, and the engagement claw 9a at the distal end portion thereof is brought into a state of being engageable with a part of the stopper member 14.

As shown in fig. 8, the contracted wire operating cylinder 32 (see fig. 4) is again slightly expanded, the engagement claw 9a at the distal end of the swing lever 9 is engaged with a part of the stopper member 14, and the driving movement of the stopper member 14 in the left direction is temporarily stopped. In this way, in a state where the stopper member 14 is temporarily stopped, the wire hook 3 is moved to the holding position between the waiting position and the wire hanging position via the link 35 and stopped. At this time, the hook portion 3b at the tip end of the hook 3 moves to the left rear side from the hook position (needle drop position A, A) shown in fig. 5, hooks the machine needles 20a and 20b, and then holds the hook at the holding position.

As shown in fig. 9, when the output rod 41 is pushed and driven in the left direction as the stopper cylinder 42 is extended, the swing lever 9 swings counterclockwise against the swing urging force of the spring 96, and the engagement between the engagement claw 9a at the distal end of the swing lever 9 and a part of the stopper member 14 is released, thereby releasing the temporary stop of the stopper member 14. Thereby, the wire operating cylinder 32 performs the maximum extension operation to swing the wire hook 3 back to the waiting position via the link lever 35.

As described above, in the present embodiment, the thread hooking hook 3 of the needle thread holding mechanism swings among the waiting position, the thread hooking position, and the holding position described above by the extending and contracting operations of the thread operating cylinder 32 and the stopper cylinder 42.

In the horizontal tubular double-thread lockstitch sewing machine according to the present embodiment, as shown in fig. 3 to 5, the needle bed 11 attached to the upper surface of the sewing machine bed B is configured to be divided into two parts, i.e., a left needle bed part 11L and a right needle bed part 11R. The needle plate 12 is detachably attached to the upper surface of the left side needle plate base portion 11L by a setscrew 100, and supports a support shaft 30 serving as a swing center of the thread hook 3 of the needle thread holding mechanism.

Screw holes 101 are formed in a plurality of front and rear portions (two portions) near the left end portion of the left needle bed portion 11L divided into two portions, specifically, in a portion separated from the attachment portion of the needle plate 12 near the tip end (left end) of the arm portion C of the sewing machine shown by the broken line in fig. 5, and the left needle bed portion 11L is attached to the upper surface of the sewing machine bed portion B so as to be fastened or unfastened (detachably) by a setscrew member 102 screwed into the screw holes 101.

As shown in fig. 4, a positioning pin 103 and a pin hole 104 into which the positioning pin 103 is fitted are formed in the upper surface of the sewing machine bed portion B and the left needle bed portion 11L at a position separated from the two fastening positions of the stopper screw member 102, and the left needle bed portion 11L can be positioned at a predetermined position and in a predetermined posture with respect to the sewing machine bed portion B by inserting the positioning pin 103 from above into the pin hole 104, and the stopper screw member 102 is screwed into the screw hole 101 in this state, whereby the left needle bed portion 11L can be fastened to the upper surface of the sewing machine bed portion B.

In the first embodiment, the positioning pin 103 is projected upward from the upper surface of the sewing machine bed portion B and the pin hole 104 is formed in the left needle bed portion 11L, but the positioning pin 103 may be projected downward from the lower surface of the left needle bed portion 11L and the pin hole 104 may be formed in the upper surface of the sewing machine bed portion B.

On the other hand, the right side needle bed portion 11R divided into two parts constitutes a cylinder mounting portion for supporting the wire operating cylinder 32 and the stopper cylinder 42 (hereinafter, the right side needle bed portion 11R is referred to as a cylinder mounting portion), and the stopper mechanism is disposed below the cylinder mounting portion 11R. Specifically, as shown in fig. 5 to 8, the wire operating cylinder 32 is fixedly supported by the lower surface of the cylinder mounting base portion 11R by mounting screws 105, the stopper cylinder 42 is disposed in a double-layered state below the wire operating cylinder 32, and the stopper cylinder 42 is fixedly supported by the cylinder mounting base portion 11R by mounting screws 106.

The cylinder mounting base portion 11R is assembled in a fixed state to the rear surface of the sewing machine base portion B by a set screw member 107. Here, the fixed state is a state in which the thread breakage preventing device H is fixed at a predetermined position by fastening the set screw member 107 when the thread breakage preventing device H is assembled to the sewing machine base B, and is fixed at a predetermined assembly position so that position adjustment or the like cannot be performed after assembly.

One end (right end) of the connecting rod 35 is rotatably connected to the stopper member 14 of the stopper mechanism by a pin screw 108. A slit 109 that is long in the left-right direction is formed in a portion of the cylinder mounting table portion 11R corresponding to a connecting portion between one end of the connecting rod 35 and the stopper member 14 by the pin screw 108, so as to allow the linear reciprocating movement of the stopper member 14 that linearly reciprocates in the left-right direction in accordance with the expansion and contraction of the wire operating cylinder 32.

Further, a connection end portion 35a connected to the extension portion 3c connected to the wire hook 3 at the other end of the connection lever 35 is bent downward by a substantial thickness of the extension portion 3 c. A pin 110 is provided to protrude upward from the connecting end portion 35a of the connecting rod 35 bent downward, and a connecting hole 111 is formed in the extending portion 3c, and the connecting hole 111 is formed to be able to be fitted into and removed upward from the pin 110 from above the pin 110.

Thus, when the left needle bed portion 11L is released from the sewing machine base portion B and removed therefrom, the work of loosening, for example, a set screw for fixedly connecting the coupling bar 35 and the extending portion 3c to release the interlocking state therebetween is not required, and the coupling hole 111 of the extending portion 3c can be pulled out upward from the pin 110 only by lifting up the left needle bed portion 11L upward, so that the interlocking state between the coupling bar 35 and the extending portion 3c (the hook 3) can be released. Further, even when the left needle bed portion 11L is attached to the sewing machine base portion B, the coupling hole 111 can be fitted to the pin 110 from above only by moving the left needle bed portion 11L from above toward the sewing machine base portion B, and the coupling lever 35 and the extension portion 3c (the hook 3) can be returned to the interlocked state. In addition, the connecting end portion 35a of the connecting rod 35 is not necessarily bent downward. That is, the tie bar 35 may have a flat plate shape over the entire length.

A swing lever mounting base 92 that can support the swing lever 9 of the stopper mechanism and swing about a vertical support shaft 90 is mounted on the cylinder mounting base portion 11R so that the position thereof can be adjusted in the lateral direction by a slit 93 and a stopper screw 94 that are long in the lateral direction. In this way, after the cylinder mounting base portion 11R is assembled to the sewing machine bed portion B in a fixed state by the setscrew member 107, the timing at which the looper 1 is pulled out from the needle thread loops 20a2, 20B2 held by the thread hooking hook 3 can be arbitrarily adjusted by adjusting the position of the swing lever mounting base 92 with respect to the cylinder mounting base portion 11R in the left-right direction, and thus, the self-looper for preventing the thread stitch from being opened can be reliably performed.

As described above, in the transverse-tubular double-lock stitch sewing machine according to the present embodiment, the structure in which the needle bed 11 is divided into two parts, the left needle bed part 11L and the right needle bed part 11R, is adopted, and thus, when the anti-stitch-unraveling device H is assembled to the sewing machine base B, the left needle bed part 11L and the right cylinder attachment part 11R of the needle bed 11 divided into two parts in the left-right direction can be separately attached to the sewing machine base B. Therefore, as compared with a case where the left and right needle bed portions 11L and 11R are integrally configured and one needle bed is long and large in the left-right direction, the work of attaching (assembling) the main body of the thread breakage preventing device H to the base B of the sewing machine can be easily performed with less labor.

Further, when the needle bed 11 (the left needle bed 11L and the right cylinder mounting bed 11R) is assembled to the sewing machine base B once, for example, when the position and the movement locus of the looper 1 and the operation members thereof, and the like, which are members for sewing contained in the sewing machine base B at the lower portion of the needle bed 11, need to be corrected to adjust the sewing state, or when maintenance such as maintenance or replacement of various members contained in the sewing machine base B at the lower portion of the needle bed 11 is required, the cylinder mounting table 11R, which is firmly fixed and supported at a predetermined position when the thread operating cylinder 32 and the stopper cylinder 43 connected to the air feed pipes 33 and 43 are assembled, need not be removed from the sewing machine base B, and a sufficiently large working space can be secured by simply removing the left needle bed 11L from the sewing machine base B by releasing the fixation, thereby facilitating adjustment of sewing conditions and maintenance.

Next, the thread cutting mechanism 5 provided in the horizontal tubular double-lock stitch sewing machine according to the present embodiment will be described. As shown in fig. 10 to 12, the thread cutting mechanism 5 is configured such that the thread cutting device 5 can be reciprocally driven and moved by the reciprocating drive moving mechanism 70 between the advanced position P1 near the needle plate 12 and the looper 1 and the retracted position P2 to the right and rearward of the advanced position P1. Further, the thread cutting device 5 includes: a movable cutter 50 for cutting the left and right needle thread portions 20a1, 20b1 and the curved needle thread portion 10a protruding from the back side of the sewing fabric W after the predetermined sewing operation is finished, that is, when the sewing is finished; a fixed knife 51 having a blade portion 51e disposed at a position close to the needle falling position within a range not falling within the vertical reciprocating path of the right needle 2b of the left and right needles 2a, 2b at the advance position P1; a looper thread holding member 52 made of a plate spring, which is disposed below the movable knife 50 and elastically holds and holds an end of the looper thread 10 to be cut between the movable knife 50 and the looper thread holding member; and a thread holding auxiliary spring 53 for adjusting a holding force of the looper thread holding member 52.

As shown in fig. 10 and 12, the movable knife 50 is formed of a strip-shaped plate material which is long in the left-right direction, a needle thread catching portion 50b is formed at a position near the tip end of the movable knife 50 formed of the long strip-shaped plate material, the needle thread catching portion 50b catches the right and left needle thread portions 20b1 and 20a1 which protrude from the back side of the sewing material W on the needle plate 12 when the movable knife 50 is driven to move back from an outer position near the other side (left side) of the needle fall position to an outer position near one side (right side), a looper thread catching portion 50a is formed at the tip end of the movable knife 50, and the looper thread catching portion 50a is driven to move back from an outer position near the other side (left side) of the needle fall position to an outer position near one side (right side) of the movable knife 50, the curved needle part 10a protruding from the back side of the sewing material W on the needle plate 12 is hooked and caught. Then, when the movable knife 50 is driven to move backward, the needle thread portions 20b1 and 20a1 caught by the needle thread catching portion 50b and the looper thread portion 10a caught by the looper thread catching portion 50a are moved to a position on the other side (right side) than the outer position on the one side (right side) of the needle drop position, and the catching portions 50b and 50a are cut by sliding contact with the edge portion 51e of the fixed blade 51.

The reciprocating drive moving mechanism 70 configured to reciprocate the thread cutting device 5 between the advanced position P1 and the retracted position P2 and to linearly reciprocate only the movable knife 50 in the x-y direction between the outer position on one side (right side) and the outer position on the other side (left side) of the needle fall position in the state where the thread cutting device 5 has moved to the advanced position P1 is configured as shown in fig. 10, 11(a), 11(B), 12(a), and 12 (B).

That is, the lower surface of the right end of the movable knife 50 is fixed to the movable knife base 124 by a screw 123. A U-shaped notch 125 is formed at a substantially central portion in the longitudinal direction (left-right direction) of the movable cutter table 124, and a pair of left and right slits 126a, 126b that are long in the longitudinal direction of the movable cutter table 124 are formed at left and right positions across the notch 125.

The fixed knife 51 is disposed on the upper surface of the movable knife 50, and a knife table guide 127 and the right end of the looper thread holding member 52 are disposed in a superposed manner on the lower surface of the right end of the fixed knife 51. The fixed cutter 51, the cutter table guide 127, and the looper thread clamping member 52 are fixed to the left end of the fixed cutter table 129 by screws 128. The movable cutter table 124 is sandwiched between a headed bolt 148 inserted through the rear surface (lower surface) of the fixed cutter table 129 and flanged cylindrical nuts 131a, 131b inserted from the upper surface side at one end portions of the pair of left and right links 140a, 140b, and the flanged cylindrical nuts 131a, 131b allow a state in which the one end portions of the pair of left and right links 140a, 140b are rotated and a state in which the one end portions are slidable within the length range of the pair of left and right slits 126a, 126b in the movable cutter table 124.

Flanged sleeves 141a, 141b inserted from the upper surface side of the other end portions of the pair of left and right links 140a, 140b and allowed to rotate in the other end portions of the pair of left and right links 140a, 140b are screwed to the device mounting base 130 by grub screws 142a, 142 b. Accordingly, the movable cutter table 124 and the fixed cutter table 129 are supported by the apparatus mounting table 130 in a state of being capable of reciprocating in the left-right direction in accordance with the swinging motion of the pair of left and right links 140a, 140 b.

Further, the right flanged sleeve 141b of the flanged sleeves 141a, 141b is formed in an eccentric cam shape, and by changing the pitch of the holes at both ends of the right link 140b, the position of the movable knife 50 at the advancing position P1 of the thread cutting device 5 with respect to the needle drop position and the advancing movement starting point in the fabric conveying direction of the looper 1 can be finely adjusted with the flanged sleeve 141a of the left link 140a as a fulcrum.

A contact member 134 is formed on the fixed cutter table 129, and the contact member 134 is in contact with a stopper member 133 screwed and fixed to the device mounting table 130 at a position below the left link 140a of the pair of left and right links 140a, 140 b.

Further, an engagement projection 136 is formed at a rear portion of a central portion in the longitudinal direction of the fixed cutter table 129, and the engagement projection 136 is brought into contact with and separated from a projection 135 projecting rearward from a position slightly to the right of the left end of the movable cutter table 124. The engagement projection 136 abuts on the projection 135, and the movable cutter table 124 cannot be moved further rightward by itself. The movable cutter table 124 is screwed to the device mounting table 130, and one end portion thereof is elastically urged to move in the left direction by a spring 137 which is elastically in contact with the right end surface of the contact member 134.

The device mounting base 130 is formed with a groove 146 into which the fixed cutter base 129 is slidably fitted in the left-right direction, and is fixed to the sewing machine base B by a plurality of screws 147 arranged around the groove. Further, a drive rod 145 is attached to the device mounting base 130, and the drive rod 145 is pivotally connected to the distal end portion of a piston 148 of the thread cutting cylinder 48 by a stepped screw 143, and is capable of driving and swinging in the arrow a-b direction about a shaft 144 on the device mounting base 130. The thin circular portion 145a at the tip end of the drive lever 145 engages with a U-shaped notch 125 formed in the substantially central portion of the movable cutter table 124.

According to the reciprocating drive movement mechanism 70 configured as described above, as shown in fig. 11(a) and 11(B), when the drive rod 145 is driven and swung in the B direction by the extension of the piston 148 of the thread cutting cylinder 48, the thread cutting device 5 moves rightward against the elastic force of the spring 137 to bring the engagement protrusion 136 into contact with the protrusion 135, and the cylindrical nuts 131a and 131B of the pair of left and right links 140a and 140B move to come close to the leftmost position in the pair of left and right slits 126a and 126B, and the left end surface of the contact member 134 of the fixed cutter table 129 is separated from the stopper member 133. In this state, the thread cutting device 5 is located at the retracted position P2 and waits in an inclined posture so as not to hinder the movement of the looper 1.

Next, as shown in fig. 12(a) and 12(B), when the drive rod 145 is driven and swung in the a direction by the contraction of the piston 148, the contact member 134 that fixes the cutter table 129 is moved to the left side by the elastic force of the spring 137. Accordingly, in the state where the engagement projection 136 abuts against the projection 135, the thread cutting device 5 is moved leftward while decreasing the inclination angle of the inclined posture by the swing of the pair of right and left links 140a and 141b until the left end surface of the abutment member 134 of the fixed cutter table 129 abuts against the stopper member 133. Thereby, the thread cutting device 5 moves to the advance position P1, and is in a posture substantially orthogonal to the sewing traveling direction.

When the piston 148 is further contracted from this state and the drive rod 145 is driven to swing in the a direction, the fixed cutter table 129 is held at the advance position P1, and the movable cutter table 124 is moved in the left direction (x direction) by the needle fall position of the needle plate 12. That is, only the movable knife 50 fixed to the movable knife table 124 moves leftward (forward movement) between the needle plate 12 and the looper 1. At this time, the movable cutter table 124 and the fixed cutter table 129 are supported on the apparatus mounting table 130 in a state of being capable of reciprocating in the left-right direction in accordance with the swinging motion of the pair of left and right links 140a, 140b, and therefore the movable cutter 50 is controlled to be capable of linearly moving by the pair of left and right links 140a, 141 b.

Subsequently, the drive rod 145 is driven to swing in the direction b by extending the piston 148. Accordingly, the movable knife 50 moves from the leftmost position to the right (y direction) and moves back (backward movement) to the right to the lower portion of the fixed knife 51 waiting at the forward position P1. When the piston 148 further contracts from this state, the thread cutting device 5 moves backward to the retreat position P2 shown in fig. 11(a) and 11 (B).

In addition to the above-described configuration and apparatus, the double-lock stitch sewing machine of the present embodiment further includes a looper thread pulling-back force applying device 84.

As shown in fig. 1 and 2, the looper thread pulling-back force applying device 84 is disposed inside the sewing machine base B above the reciprocating drive moving mechanism 70 of the thread cutting device 5. The looper thread pulling-back force applying device 84 includes: a plurality of looper thread guides 150 fixedly provided for feeding and guiding a looper thread portion 10a, which is hung between a looper thread supply source device such as a thread tension plate (which is known and therefore not shown in the drawings and a description of a specific structure thereof) and the looper 1, substantially linearly; a swing arm 152 that is capable of swinging back and forth between a position facing the looper thread guide 150 and a front side position in a horizontal or substantially horizontal plane with a position close to the looper thread supply source device as a fulcrum shaft 151; and an actuator 153 for driving the swing arm 152 to swing back and forth between the two positions, wherein a looper thread hooking portion 154 is attached to a tip end portion of the swing arm 152, and the looper thread hooking portion 154 hooks a looper thread portion 10a of a looper thread guide 150a close to the looper thread guide 150a of the looper thread supply source device among looper thread portions 10a between two looper thread guides 150a and 150b provided to face each other at a short distance from each other among the plurality of looper thread guides 150.

As shown in fig. 14, the actuator 153 includes a combination of the following components: a spring 153a for biasing the swing arm 152 to swing the looper thread hooking part 154 forward from a position facing the looper thread guide 150a toward the front side position; and a single-acting telescopic fluid pressure (air pressure) cylinder 153b that, as shown in fig. 13, acts on an arm portion 152a extending integrally substantially perpendicularly to the swing arm 152 to swing the looper thread hooking portion 154 of the swing arm 152 back and forth from the front side position toward a position facing the looper thread guide 150 a.

The looper thread pulling-back force applying device 84 configured as described above operates to change from the state of fig. 13 to the state of fig. 14 during the advancing operation of the looper 1 after the thread is looped around. Thus, the looper thread part 10a is bent forward and sideways so as to form one straight side and a hypotenuse of a substantially right triangle in plan view, and a pulling force toward the looper thread supply device side is applied to the looper thread part 10a supplied from the looper thread supply device to the looper 1. As a result, it is possible to eliminate the slackening of the looper thread 10 due to the operation necessary for obtaining the thread unraveling prevention effect of the self-looper in which the looper thread 10 is held by the looper thread holding body 6 at the front side of the needle descent position after the normal sewing is completed.

In addition, since the spring 153a for applying the pulling force to the looper thread part 10a in the actuator 153 of the looper thread pulling-back force applying device 84 may cause sewing wrinkles or the like when an excessively large pulling force is applied to the looper thread part 10a, it is preferable to set the spring force to be an elastic force that can apply a pulling force of such a degree that sewing wrinkles or the like are not generated appropriately.

Fig. 15 is a block diagram showing a configuration of a control system of the transverse tubular double-lock stitch sewing machine including the above-described anti-stitch-breaking device H and the thread cutting device 5 according to the present embodiment.

A step-in (forward step) signal 21a and a step-back (backward step) signal 21b from a pedal switch 21, a needle position signal 22, a thread cutting signal 23, and a needle thread removal signal 24 transmitted when the needles 2, 2 are located near the top dead center are input to the control unit 8 of the double-thread lockstitch sewing machine.

On the other hand, the control unit 8 outputs operation control signals to the wire operating cylinder 32, the limit cylinder 42, and the wire cutting cylinder 48, respectively. The thread hooking hook 3 and the looper thread holder 6 are operated as described above based on the operation control signals output from the control unit 8 to the thread operating cylinder 32 and the stopper cylinder 42, and the thread cutting cylinder 48 is respectively extended and contracted based on the thread cutting signal 23 output from the control unit 8.

Further, the operation control signals are output from the control section 8 to a sewing machine motor 80 as a drive source for driving the rotation shaft, a presser foot cylinder 81 for raising and lowering the presser foot, an air brush 82 for raising the cut machine needle threads 20a and 20b as described later, a feed reducing mechanism 83 for adjusting the feed amount of the sewing material, and a looper thread pulling-back force applying device 84.

The feed reducing mechanism 83 is known, and therefore, the feed amount of the sewing material is reduced by changing the operation form of the feed dog in the feed mechanism, for example, by inclining the operation path of the feed dog with respect to the needle plate 12 to shorten the protrusion time to the needle plate P, thereby shortening the time for the feed dog to act on the sewing material on the needle plate 12, or by changing the length of the rod for circulating the feed dog to reduce the unit feed pitch of the feed dog, etc., and the feed reducing mechanism 83 is not shown in detail and will be described.

After completion of sewing of the stitch for forming the double lock stitch, the control section 8 operates the hook 3 in association with the sewing machine motor 80, the presser foot cylinder 81, the air brush 82, the feed reducing mechanism 83, and the looper thread pull-back force applying device 84, thereby performing the operation of preventing the stitch from being opened and the thread cutting operation for the double lock stitch.

Fig. 16 is a time chart showing the operation contents of the control unit 8 for preventing the stitches from being opened in time series. The control unit 8 is a computer including a CPU, a ROM, and a RAM, and the open-line prevention operation and the thread cutting operation according to the timing chart of fig. 16 are executed by a series of operations of the CPU based on a control program stored in the ROM.

Fig. 17 to 22 are explanatory views of the thread breakage preventing operation by the thread breakage preventing device H of the horizontal tubular double-thread lockstitch sewing machine according to the present embodiment, and show the operation states of the thread hanging hook 3 and the looper thread holding body 6 by the operation of the control unit 8 according to the timing chart of fig. 16.

When a sewing operator using a sewing machine stops the stepping operation of a pedal for driving the sewing machine at the end of normal sewing, the sewing operator performs a thread-open preventing operation, and in this case, performs a stepping-back operation of the pedal. The pedal switch 21 is provided on a pedal, and outputs a depression signal 21a when a depression operation is performed and a depression return signal 21b when a depression return operation is performed.

When normal sewing is completed and the pedal for driving the sewing machine is returned from the depressed state to the neutral state at time S1 in fig. 16, that is, when the pedal switch 21 is in a state in which neither the depression signal 21a nor the kick-back signal 21b is output, the control unit 8 refers to the needle position signal 22 supplied to the input side and outputs a stop command to the sewing machine motor 80. Thereby, the sewing machine is temporarily stopped in a state where the loopers 1 are advanced leftward with the sewing needles 2a and 2b positioned near the top dead center.

Then, the control unit 8 waits until the pedal is operated to be stepped back. When the kick-back signal 21b is input to the input side by the kick-back operation at time S2 in fig. 16, the control unit 8 first gives an operation start command to the feed reducing mechanism 83 at time S3 to reduce the feed pitch of the feed dog unit so that the feed amount of the sewing fabric becomes smaller (reduced) than the feed amount in normal sewing, and then starts the thread breakage preventing operation described below. The feed reducing mechanism 83 sets the feed dog to feed the sewing material at a small feed amount (S3) before the needle where the needle loops 20a2 and 20b2 are positioned on the forward end side of the looper 1 from the lowering position of the needles 2a and 2b by the hook 3.

Further, since the control unit 8 resumes the normal sewing operation when the step-in signal 21a is input again from the pedal switch 21, the sewing operator can continue the normal sewing operation by performing the step-in operation again on the pedal. In fig. 15, the neutral state is maintained from the time point S1 to the time point S2, but the neutral state is not necessarily maintained, and the normal pedal operation at the end of sewing may be continuously switched from the depressed state to the depressed state. In this case, when the shift process passes through the neutral position, the stepping-in signal 21a and the stepping-back signal 21b are in a no-signal state in which neither is output, and the control unit 8 starts the open-prevention operation after the state in which the needles 2a and 2b are raised near the top dead center and the looper 1 is moved leftward is realized as described above with the no-signal state as a trigger signal.

In the timing chart of fig. 16, the pedal return operation at time S2 is continued when the anti-open operation described below is performed, but it is not necessary to continue such a pedal return operation until the anti-open operation is completed, and the anti-open operation is continued by the control of the control unit 8 after the input of the pedal return signal 21b is stopped.

Fig. 17 shows the state of the needles 2a and 2b, the looper 1, the thread hooking hook 3, and the looper thread holding body 6 at the start of the thread separation preventing operation. The needles 2a and 2b are drawn out above the sewing fabric in a state where a double lock stitch seam M is formed by two machine needles 20a and 20b and one looper thread 10. The looper 1 is in a state of grasping the needle thread loops 20a2, 20b2 formed by the needles 2a, 2b on the lower left side of the sewing fabric. In this state, if the cutter threads 20a and 20b and the looper thread 10 are cut, a normal sewing finish portion where thread breakage is likely to occur is formed as shown in fig. 24.

After the start of the disconnection preventing operation, the control unit 8 first gives an operation command to the output-side wire operating cylinder 32 at time S2 in fig. 16. As a result, the wire operating cylinder 32 is operated from the extended state shown in fig. 6 to the retracted state shown in fig. 7, the stopper member 14 is driven to move in the right direction, and the wire hook 3 swings about the support shaft 30 via the stopper member 14 and the link 35, and moves from the waiting position to the wire hanging position. At this time, the hook portion 3b at the tip end of the hook 3 hooks one needle loop 20a1, and the swing lever 9 in the stopper mechanism swings clockwise around the support shaft 90 by the urging force of the spring 96, so that the engagement claw 9a at the tip end thereof can be engaged with a part of the stopper member 14.

Next, the control unit 8 gives an operation command to the wire operating cylinder 32, and the wire operating cylinder 32 is slightly extended from the state shown in fig. 7 to the state shown in fig. 8, and the drive stopper member 14 linearly moves to the left side. When the wire operating cylinder 32 is slightly extended, the engagement claw 9a at the distal end of the swing lever 9 also engages with a part of the stopper member 14. Thereby, the driving movement of the stopper member 14 in the left direction is temporarily stopped. In this way, in a state where the driving movement of the stopper member 14 in the left direction is temporarily stopped, as shown in fig. 18, the thread hooking hook 3 is moved to the holding position between the waiting position and the thread hooking position via the connecting link 35 and then stopped, the hook portion 3b at the tip holds the needle thread loop 20a2 at the holding position, and as shown in fig. 19, the looper thread holder 6 is advanced to the front side of the looper 1, and the looper thread 10 is held by the looper thread holder portion 6a at the tip in front of the needle falling position a on the left side. As a result, when the looper thread holder 6 is returned to the waiting position, the looper thread 10 released from the looper thread holder 6 is loosened.

As shown in fig. 20, the holding of the needle thread 20a, 20b and the looper thread 10 by the hook 3 and the looper thread holder 6 is continued until the feeding of the sewing fabric is completed and the needle 2a, 2b passes through the needle thread loop 20a2 held by the hook 3 and catches the needle thread loop 20a 2. At this time, the looper thread 10 held by the looper thread holding member 6 is provided so as to cross the front side of the left needle 2a as shown in fig. 20. Therefore, the left-hand needle 2a does not catch the looper thread 10, and the looper thread 10 is caught only by the right-hand needle 2b at the rear side of the looper 1.

As described above, after the movement of the hook 3 and the looper thread holder 6 is stopped at the respective positions, the control unit 8 issues an operation command to the sewing machine motor 80 at time S3 in fig. 16. The operation command is issued while the needles 2a and 2b are lowered and then raised again to the position near the top dead center with reference to the needle position signal 22. Thus, the sewing fabric is sewed by one needle. The sewing of the stitch is performed in a state where the feed amount is smaller than that in the normal sewing by the operation of the feed reducing mechanism 83.

Next, at a time S4 in fig. 16, the control unit 8 gives an operation command to the stopper cylinder 42 of the stopper mechanism, and causes the stopper cylinder 42 to extend, thereby driving the output rod 41 to push it in the left direction. As a result, as shown in fig. 9, the swing lever 9 swings counterclockwise against the swing urging force of the spring 96, and the engagement between the engagement claw 9a at the tip end of the swing lever 9 and a part of the stopper member 14 is released, thereby releasing the temporary stop of the stopper member 14. Thus, by releasing the stop of the stopper member 14, the wire operating cylinder 32 is extended to the maximum at time S4. As a result, as shown in fig. 20, the hook 3 and the looper thread holder 6 swing about the support shaft 30 via the stopper member 14 and the link 35, and return-move from the holding position to the waiting position.

At a time S4 in fig. 16, in which the stopper cylinder 42 is extended and the thread operating cylinder 32 is extended to the maximum extent, the control unit 8 operates the looper thread pulling force applying device 84. Thereby, a pulling-back force toward the looper thread supply source device is applied to the looper thread 10 released from the looper thread holding body 6, and the slackening of the looper thread 10 is eliminated. Specifically, the retractable fluid pressure cylinder 153b as one of the actuators 153 of the looper thread pulling-back force applying means 84 is retracted, and the swing arm 152 is swung forward around the fulcrum shaft 151 by the biasing force of the spring 153a as the other of the actuators 153, and as shown in fig. 14, the looper thread hooking portion 154 at the arm tip end thereof is swung forward from a position facing the looper thread guide 150a to the front side position. As a result, the looper thread part 10a is bent forward and sideways so as to form one straight side and a hypotenuse of a substantially right triangle in plan view, and a pulling force toward the looper thread supply source device side is applied to the looper thread part 10a supplied to the looper 1. As a result, it is possible to eliminate the slackening of the looper thread 10 due to the operation necessary for obtaining the thread unraveling prevention effect of the self-looper in which the looper thread 10 is held by the looper thread holding body 6 at the front side of the needle descent position after the normal sewing is completed.

Then, the looper 1 performs a right retracting operation while the needles 2a and 2b are lowered, and is pulled out from the gripped needle thread loop 20a 2. As shown in fig. 21, by pulling out the looper 1, the right needle 2b is brought into a state of catching the looper thread 10 as in the normal sewing, and the left needle 2a is brought into a state of catching the left needle thread ring 20a 2.

In this state, the looper 1 is shifted to the left, and the needles 2a and 2b are shifted to the up. As shown in fig. 22, the left-hand looper 1 catches the needle thread loops 20a2, 20b2, and the rising needles 2a, 2b are pulled out upward above the sewn fabric. Thus, the needle thread 20a caught by the looper 1 is in a so-called self-looper state in which the needle thread loop 20a2 caught before is looped around the needle thread 20 a.

After a sewing operation, the sewing operation is finished in a state where the sewing needles 2a and 2b are raised to the vicinity of the top dead center and the looper 1 reaches the vicinity of the left feed end. When the thread cutting signal 23 is input to the control unit 8 at time S5 in fig. 16, an operation command is issued to the thread cutting cylinder 48 of the thread cutting device 5, and the thread cutting cylinder 48 is caused to perform a predetermined operation. As a result, as shown in fig. 12, the thread cutting device 5 is moved to the advanced position P1, which is an outer position on the needle drop position A, A side, by the reciprocating drive movement mechanism 70. Then, a thread cutting operation is performed, and the thread cutting operation will be described in detail below with reference to fig. 23.

First, as shown in fig. 23(a), at the end of sewing, the thread cutting device 5 is moved to the forward position P1, which is the outer position on one side of the needle fall position, and then, as shown in fig. 23(b), only the movable knife 50 is moved forward in the arrow x direction from the forward position P1 toward the outer position on the other side of the needle fall position. As shown in fig. 23(c), by this forward driving movement, immediately after the looper thread catching portion 50a on the tip end side of the movable knife 50 passes over the looper thread 10 caught between the vicinity of the tip end of the looper 1 and the back surface side of the sewing fabric W, the moving direction of the movable knife 50 is reversed, and the looper thread portion 10a protruding from the back surface side of the sewing fabric W is caught by the looper thread catching portion 50 a.

Next, as shown in fig. 23(d), the movable knife 5 is driven to move back in the arrow y direction from the outer position on the other side of the needle drop position toward the advance position P1, and the left and right needle thread portions 20a1, 20b1 protruding from the back surface side of the sewing fabric W are caught by the needle thread catching portion 50b and caught. Then, the movable knife 50 is further driven and moved back in the arrow y direction, whereby the needle thread portions 20a1 and 20b1 caught by the needle thread catching portion 50b and the looper thread portion 10a caught by the looper thread catching portion 50b are cut by the sliding contact of the catching portions 50a and 50b with the fixed knife 51 as shown in fig. 23 (e).

Then, as shown in fig. 23(f), the needles 2a and 2b move upward of the needle plate 12, and the end of the looper thread 10 held by the looper 1 is elastically held between the movable knife 50 and the looper thread holding member 52.

The looper thread pulling-back force applying means 84 continues to operate until the above-described thread cutting operation is completed, and continues to apply a predetermined pulling-back force to the looper thread 10 extending from the tip end of the looper 1 to the sewing fabric. Accordingly, as shown in fig. 22 and 24, even if the needles 20a and 20b located on the rear side (near side in fig. 24) of the looper 1 move downward as indicated by an arrow d as the needles 2a and 2b rise to the vicinity of the top dead center after one sewing operation, the looper thread 10 does not slacken, and therefore the looper thread 10 is not caught under the looper 1 by sliding contact with the needles 20a and 20 b.

Therefore, when the thread cutting device 5 is operated and the movable knife 50 is moved forward in the arrow x direction from the forward position close to the left front of the looper 1 to the outer position close to the other side (left side) of the needle drop position as shown in fig. 23(b) and 23(c), the looper thread catching portion 50a on the tip side of the movable knife 50 can reliably catch the looper thread 10 caught between the vicinity of the tip of the looper 1 and the back side of the sewing material W, and the machine thread catching portion 50b of the movable knife 50 can reliably catch the machine threads 20a and 20b and reliably cut them by sliding contact with the fixed knife 51, whereby the end of the cut looper thread 10 is reliably held between the movable knife 50 and the looper thread holding member 52.

Therefore, the cutting failure due to the slackening of the looper thread 10 from the thread loop and the failure in holding the looper thread after cutting can be eliminated, and the next sewing can be performed reliably and with good appearance as prescribed.

After the thread cutting operation is completed, the thread cutting device 5 is moved to the retreat position P2 shown in fig. 11(a) and 11(B) by the reciprocating drive moving mechanism 70, and waits for the next sewing in an inclined posture in which the movement of the looper 1 is not hindered. On the other hand, the control unit 8 waits until the needle thread removing signal 24 is input, and outputs an operation command to the air brush 82 to operate the air brush 82 when the needle thread removing signal 24 is input at time S6 in fig. 16. The air brush 82 ejects air to jump up the cut ends of the needle threads 20a and 20b connected to the needles 2a and 2 b. Then, the control unit 8 outputs an operation command to the presser cylinder 81 at a time S7 in fig. 16 to operate the presser cylinder 81, thereby raising the presser from the upper surface of the needle plate 12, and thereby taking out the sewing material W that has been prevented from being opened by the self-looper for the next sewing.

In the sewing operation of one needle for preventing the thread from being opened as described above, as shown in fig. 26, the looper thread 10 is passed through the right needle ring 20b2 formed on the back surface of the sewing material W at the end of the stitch M, is folded back in front of the right needle ring 20b drawn out to the back surface of the sewing material W at the time of the one-stitch-amount preventing operation, is again passed through the final needle ring 20b2 on the right side, and is drawn out and cut.

On the other hand, in the sewing operation of a needle for preventing thread breakage, the left needle thread portion 20a1 drawn out to the back surface of the sewing fabric W passes through the final needle thread loop 20a2 formed in the back surface of the sewing fabric W after the end of the normal sewing operation, and the final needle thread loop 20a2 is looped by itself to form the seam M of the single-loop sewing. Therefore, as shown in fig. 26, the looper thread 10 is firmly pressed by the needle thread 20a and the final needle thread loop 20b2, and is caught between the final needle thread loop 20b2 on the left side and the needle thread loop 20c formed last time. This restriction can be maintained regardless of the direction of the force applied to the curved needle portion 10a, and therefore, the specific opening of the stitches M of the double lock stitch can be prevented.

In addition, in the sewing operation of one needle for preventing the thread from being opened, the stitch pitch generated by the other thread winding before the thread winding can be made smaller than the stitch pitch generated by the other thread winding before the thread winding by making the feed amount of the sewing material fed by the feed dog of the feed reducing mechanism 83 smaller than the feed amount in the normal sewing. This enhances the pressing of the looper portion 10a between the left needle thread 20a and the left final needle thread ring 20a2, thereby increasing the resistance against separation. Therefore, in the state shown in fig. 26, the opening of the stitch M of the double lock stitch can be reliably prevented by the cooperation of the self-looper portion and the stitch pitch decreasing by the other thread-looper before the self-looper to increase the thread take-off preventing resistance of the looper thread 10.

In the above embodiment, the structure in which the looper thread holder 6 is moved closer to or farther from the looper 1 integrally with the looper 3 of the needle thread holding mechanism has been described, but the structure in which the looper thread holder 6 is moved closer to or farther from the looper 1 separately from the looper 3 of the needle thread holding mechanism may be adopted.

In the above embodiment, the structure in which the looper thread holder 6 is advanced to the front side of the looper 1 and the looper thread holder 6a at the tip end holds the looper thread 10 in front of the needle fall position A, A has been described, but the looper thread holder 6 may be advanced to the rear side of the looper 1 and the looper thread holder 6a at the tip end holds the looper thread 10 in the rear of the needle fall position A, A.

In the above embodiment, the needle bed 11 on which the thread separation preventing device H is mounted is divided into the left needle bed portion 11L and the right needle bed portion 11R, and thus the workability of assembling the thread separation preventing device H to the sewing machine base portion B and the easiness of maintenance are improved, but as the needle bed 11 of the thread separation preventing device H, an integral structure which is long in the left-right direction as in the related art may be adopted.

In the above embodiments, the two-needle horizontal tubular double-lock stitch sewing machine is applied, but the present invention can also be applied to a one-needle horizontal tubular double-lock stitch sewing machine and a flat bed double-lock stitch sewing machine.

Claims (5)

1. A double-chain stitch sewing machine with a thread-open preventing device, characterized by comprising: a needle that holds a needle thread and moves up and down; and a looper which can hold a looper thread and perform a retracting operation in a direction substantially orthogonal to an up-and-down moving path of the needle, and grasp a needle loop formed below a needle plate by the needle at the time of the advancing operation, wherein a double lock stitch is formed on a sewing material by performing other thread winding on the needle loop grasped by the advancing operation of the looper with the looper held by the looper,

the trace disconnection preventing device includes:

a needle thread holding mechanism capable of performing an operation of moving closer to or away from the looper, the needle thread holding mechanism holding a needle thread loop caught by the looper at a position closer to a forward end side of the looper than a descending position of the needle at the time of the approaching operation; a looper thread holding mechanism capable of moving closer to or away from the looper, the looper thread holding mechanism holding a looper thread extending from the looper to a sewing fabric at a position forward or backward of a lowering position of the needle during the approaching movement; and

a control part which controls the contact and separation actions of the needle thread holding mechanism and the looper thread holding mechanism in relation to the actions of the needle and the looper and the feeding action of the sewing fabric,

after the normal sewing is finished by positioning the looper at the advancing position and positioning the needle at the raising position, the control unit causes the needle thread holding mechanism and the looper thread holding mechanism to perform a closing operation to hold the needle thread loop at a position closer to the advancing end side of the looper than the lowering position of the needle and to hold the looper thread at a position closer to the front side or the rear side than the lowering position of the needle, maintains the state until the needle descends after passing through the needle thread loop caught by the looper, then releases the position holding of the needle thread loop, and performs a sewing operation of at least one needle thread loop including the descending operation of the needle after passing through the needle thread loop based on the lowering and raising of the needle, the advancing and retreating operation of the looper, and the feeding operation of the sewing fabric, thereby preventing the needle thread loop held by the needle thread held by the needle from being wound by the needle held by the needle thread to prevent the needle held by the looper from being wound around the needle thread The wire is opened, and the wire is cut,

the double-thread lockstitch sewing machine with the anti-thread-mark-opening device is provided with:

a looper thread pulling-back force applying device which hooks a looper thread portion hung between the looper thread supply source device and the looper and moves the looper thread portion to the side during the forward movement of the looper after the thread looping, thereby bending the looper thread portion and applying a pulling-back force toward the looper thread supply source device to the looper thread portion supplied to the looper,

at least two looper thread guides for guiding a looper thread portion hung between the looper thread supply source device and the looper to move substantially linearly are provided between the looper thread supply source device and the looper,

the looper thread pulling-back force applying device includes:

a swing arm capable of swinging back and forth between a position facing the looper thread guide and a lateral position where the looper thread is partially bent in a horizontal or substantially horizontal plane with a position close to the looper thread supply source device as a fulcrum shaft;

a looper thread hooking portion attached to a distal end portion of the swing arm and capable of hooking a looper thread portion of a looper thread guide on a side closer to the looper thread supply source device out of the two looper thread guides; and

an actuator that drives the swing arm to swing reciprocally between two positions.

2. The double lockstitch sewing machine with a trace opening preventing device according to claim 1, wherein:

the actuator of the looper thread pulling-back force applying device comprises a combination of:

a spring for biasing the swing arm to swing forward from a position facing the looper thread guide to the side position; and

and a fluid pressure cylinder that drives the swing arm to swing back from the side position to a position facing the looper thread guide against the biasing force of the spring.

3. The double lockstitch sewing machine with a trace opening preventing device according to claim 1, wherein:

the control unit is configured to: the sewing operation of the at least one needle for the self-looper is performed when the conveyance of the sewing fabric is stopped or the conveyance operation is performed with a smaller amount of feed than in normal sewing.

4. The double lockstitch sewing machine with a trace opening preventing device according to claim 1, wherein:

the looper thread holding mechanism is configured to: the needle thread holding mechanism can be integrated with the needle thread holding mechanism to perform the action of approaching or separating from the curved needle.

5. The double lockstitch sewing machine with a trace opening preventing device according to claim 1, wherein:

the needle thread holding mechanism includes: a thread hooking hook which swings in a plane substantially parallel to the needle plate around a vertical fulcrum between a waiting position away from the looper and a thread hooking position close to the looper; and a hook actuator that drives the wire hook to swing between the waiting position and the wire hanging position, and

the trace disconnection preventing device further includes:

a stopper mechanism including a stopper member disposed at a position farther from the needle plate than the needle thread hanging hook of the needle thread holding mechanism, the stopper member being capable of temporarily stopping or stopping the swing of the needle thread hanging hook from the needle thread hanging position to the standby position so that the needle thread loop caught by the needle thread hanging hook at the needle thread hanging position is held at a holding position between the needle thread hanging position and the standby position;

a stopper actuator for stopping and stopping the stopper member; and

a connecting member for linking the needle thread holding mechanism with the stopper of the stopper mechanism, wherein,

the control unit selectively controls the hook actuator and the stopper actuator, and the control unit causes the loop of the needle thread caught by the thread hooking hook at the thread hooking position to be held between the thread hooking position and the waiting position by abutting against the stopper member.

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