CN109234928B - Thread trimming mechanism and sewing machine - Google Patents

Abstract

The invention provides a thread cutting mechanism and a sewing machine, wherein the thread cutting mechanism comprises a fixed cutter with a fixed cutter cutting edge, a movable cutter with a movable cutter cutting edge and a thread cutting cutter seat, the fixed cutter and the movable cutter are movably arranged on the thread cutting cutter seat, the fixed cutter and the movable cutter can move together in a direction close to or far away from a machine needle in the sewing machine, the movable cutter can move in a direction close to or far away from the machine needle in the sewing machine relative to the fixed cutter, and the movable cutter is provided with a thread hooking part on one side of the movable cutter cutting edge far away from the machine needle. In this application, design into movablely with stationary knife or cutting knife for move the interlock position of sword cutting edge and stationary knife cutting edge when trimming, or the tangent line tool bit on the cutting knife is close to more in the eedle, this application can carry out the trimming in the position department that is close to the eedle center more promptly, thereby it is shorter to guarantee to remain the end of a thread on the sewing material after the trimming, realizes the trimming effect of stub end.

Description

Thread trimming mechanism and sewing machine

Technical Field

The invention relates to a thread trimming mechanism.

The invention also relates to a sewing machine comprising the thread cutting mechanism.

Background

At present, a thread cutting mechanism is provided in a sewing machine for cutting a thread (including an upper thread and a lower thread) after sewing is completed. As shown in fig. 1, the conventional thread trimming mechanism includes a movable blade 100 and a fixed blade 200, which are disposed opposite to each other, and the movable blade 100 and the fixed blade 200 are both disposed below a needle plate 300 and above a rotating shuttle 400 in a sewing machine, wherein the fixed blade 200 is fixed on a sewing machine base, and the movable blade 100 can rotate around a lower shaft in the sewing machine under the action of a driving assembly. When the sewing is finished and the thread is cut off, the driving component drives the movable knife 100 to rotate towards the direction close to the fixed knife 200, and the knife point of the movable knife 100 drives the thread to move towards the direction close to the fixed knife 200 together until the movable knife 100 and the fixed knife 200 are mechanically occluded with high pressure at one side of the needle 500 and the thread is cut off; thereafter, the movable blade 100 is restored by the spring. However, the above-described thread trimming mechanism cannot achieve the effect of short-end thread trimming because the length of the thread end remaining in the work material after the thread trimming is performed. Meanwhile, a certain length of the upper thread end remains on one side of the machine needle 500 after thread trimming to ensure that the sewing can be started normally in the next sewing, and the remaining upper thread end can form a bad stitch (i.e. bird's nest) in the first few needles of the next sewing to influence the quality of the sewing product.

In order to solve the problem of the seam bird nest, the following methods are adopted in the industry at present: the sliding thread clamping device used for clamping the upper thread end is arranged on the machine head, the blade is arranged on the presser foot, the blade on the presser foot is arranged on the upper thread end head through the sliding thread clamping device and the pulling of the suture during the seam starting, and then the upper thread end is cut off, so that the problem of 'bird nest' is solved. Although the method can solve the problem of the seam bird nest, a series of problems that the operation space is influenced after the machine head is additionally provided with the sliding thread clamping device, the presser foot with the blade is not universal, the blade of the coarse thread is cut continuously, the cut thread end of the upper thread needs air suction collection treatment, air suction needs an air source, the thread end of the upper thread is remained on the front surface of the sewing material due to thread cutting of the presser foot, and the attractiveness is influenced exist.

Disclosure of Invention

In view of the above-mentioned drawbacks of the prior art, an object of the present invention is to provide a thread trimming mechanism capable of achieving a thread trimming effect of a stub.

In order to achieve the purpose, the invention provides a thread cutting mechanism, which comprises a fixed cutter with a fixed cutter cutting edge, a movable cutter with a movable cutter cutting edge and a thread cutting tool apron, wherein the fixed cutter and the movable cutter are movably arranged on the thread cutting tool apron, the fixed cutter and the movable cutter can move together towards or away from a machine needle in a sewing machine, the movable cutter can move towards or away from the machine needle in the sewing machine relative to the fixed cutter, and the movable cutter is provided with a thread hooking part at one side of the movable cutter cutting edge away from the machine needle; when the thread is cut, the movable cutter firstly moves towards the direction close to the machine needle relative to the fixed cutter, so that a thread hooking groove is formed between the thread hooking part of the movable cutter and the fixed cutter; then the movable knife and the fixed knife move together towards the direction close to the needle, so that the suture is allowed to enter the thread hooking groove; then the movable knife moves relative to the fixed knife in the direction far away from the needle, so that the cutting edge of the movable knife is meshed with the cutting edge of the fixed knife, and the suture in the thread hooking groove is cut off; and then the movable knife and the fixed knife move together in the direction away from the needle and reset.

The thread trimming mechanism further comprises a pressing sheet movably mounted on the thread trimming cutter seat and capable of moving along with the fixed cutter, the pressing sheet, the fixed cutter and the movable cutter are sequentially arranged from top to bottom, and one end, facing the needle, of the pressing sheet is provided with a clamping part located between the cutting edge of the fixed cutter and the needle; when the upper thread end is sewn and trimmed, the movable knife drives the upper thread end in the thread hooking groove to move relative to the fixed knife in the direction away from the machine needle, so that the clamping part of the pressing sheet and the movable knife clamp the upper thread end; after the sewing machine at least completes the second needle thread locking, the movable cutter drives the upper thread end in the thread hooking groove to continue to move towards the direction far away from the machine needle relative to the fixed cutter until the cutting edge of the movable cutter is meshed with the cutting edge of the fixed cutter.

Furthermore, the thread trimming mechanism also comprises an axial position screw fixed on the thread trimming cutter holder, a first limit stop block with one end hinged to the thread trimming cutter holder, a second limit stop block with one end hinged to the thread trimming cutter holder, and a reset torsion spring sleeved on the axial position screw, wherein two ends of the reset torsion spring are respectively connected with the first limit stop block and the second limit stop block; the fixed knife and the pressing sheet are both provided with a first limit protruding part and a second limit protruding part which are oppositely arranged along the moving direction of the fixed knife; when the fixed knife and the pressing sheet move to the knife-out limit position in the direction close to the machine needle, the first limit stop block abuts against the first limit protruding part on the fixed knife and the pressing sheet; when the fixed knife and the pressing sheet move to the knife return limit position in the direction away from the machine needle, the second limit stop block abuts against the second limit protruding part on the fixed knife and the pressing sheet.

Furthermore, the movable knife is provided with a first pushing part capable of pushing the first limit stop block to swing and a second pushing part capable of pushing the second limit stop block to swing.

Further, the thread trimming mechanism further comprises a thread trimming driving source and a thread trimming transmission assembly, the thread trimming driving source is connected with the movable cutter through the thread trimming transmission assembly and drives the movable cutter to translate, and the movable cutter can drive the fixed cutter and the pressing sheet to translate together.

Furthermore, the output end of the trimming transmission assembly is provided with a transmission shifting fork capable of swinging, and the transmission shifting fork is hinged with the movable knife through a transmission pin; a first sliding groove extending along the moving direction of the moving blade is formed in the trimming cutter seat, second sliding grooves extending along the moving direction of the moving blade are formed in the fixed blade and the pressing sheet, and the length of the first sliding groove is greater than that of the second sliding groove; the tail end of the transmission shifting fork is provided with a third sliding chute; the transmission pin is respectively matched with the first sliding groove of the trimming knife holder, the second sliding grooves of the fixed knife and the pressing plate and the third sliding groove of the transmission shifting fork.

Further, the trimming transmission assembly comprises a first connecting rod, a driving shaft parallel to the middle lower shaft of the sewing machine, a driving crank and a first transmission crank fixed on the driving shaft, a second connecting rod, a second transmission crank, a third connecting rod, a transmission shifting fork and a transmission support fixed on the bottom plate of the sewing machine, the trimming driving source is provided with a telescopic trimming driving part, a wire hooking crank arm part extends from the driving crank, the two ends of the first connecting rod are hinged with the trimming driving part and the wire hooking crank arm part respectively, the two ends of the second connecting rod are hinged with the first transmission crank and the second transmission crank respectively, the two ends of the third connecting rod are hinged with the second transmission crank and the transmission shifting fork respectively, the second transmission crank and the transmission shifting fork are hinged with the transmission support, and the transmission shifting fork is connected with the movable knife.

The thread trimming transmission assembly further comprises a switching crank arm part extending from the driving crank, a sliding pin parallel to the driving shaft, a ball rotatably mounted on the sliding pin, a thread trimming cam part and an anti-bird nest cam part both fixed on the lower shaft, and a switching driving assembly for driving the sliding pin to move, wherein the sliding pin is movably mounted in the switching crank arm part, and the switching driving assembly drives the sliding pin to move axially so that the ball is abutted against the outer peripheral surface of the thread trimming cam part or the outer peripheral surface of the anti-bird nest cam part; when the thread is cut after sewing is finished, the ball is abutted with the outer peripheral surface of the thread cutting cam part; when starting sewing, the ball is firstly abutted with the peripheral surface of the bird nest prevention cam part, and after the sewing machine at least completes the thread locking of the second needle, the ball is abutted with the peripheral surface of the thread cutting cam part.

Further, the trimming cam part and the anti-nest cam part are integrated into a timing control cam.

Further, the outer peripheral surface of the trimming cam portion has a first highest reset point and a first lowest trimming start point, the outer peripheral surface of the anti-bird nest cam portion has a second highest reset point and a second lowest trimming start point, the radius of the first highest reset point is larger than that of the second highest reset point, and the radius of the first lowest trimming start point is equal to that of the second lowest trimming start point; when the ball is abutted against the first highest reset point, the cutting edge of the movable cutter is meshed with the cutting edge of the fixed cutter; when the ball is abutted against the second highest reset point, the clamping part and the movable knife of the pressing sheet are in a clamping shape; when the ball is abutted against the first lowest trimming starting point or the second lowest trimming starting point, the movable knife moves to a knife-out limit position in a direction close to the needle.

Further, switch drive assembly including be fixed in the sewing machine middle bottom plate the mounting substrate, be fixed in the mounting substrate and switch the driving source, articulate in the switching drive swing arm of mounting substrate, the knock pin that extends from top to bottom, fix the damper cap at the smooth round pin tip and the first reset spring of cover on the smooth round pin, switch the driving source and have and follow the flexible switching drive portion of smooth round pin axial, the knock pin with switch drive portion fixed connection, the knock pin can with switch drive swing arm butt, switch drive swing arm on have can with the lapse portion of damper cap butt, first reset spring's both ends respectively with switch crank arm portion and damper cap butt.

Furthermore, a guide groove extending along the moving direction of the ejector pin is formed in the mounting substrate, and the end of the ejector pin penetrates through the guide groove and is in contact with the groove wall of the guide groove.

Further, be equipped with the spacing otic placode portion that upwards extends on the mounting substrate, be fixed with the initial stopper that is located knock pin one side on the spacing otic placode portion, the termination stopper that is located the knock pin opposite side has set firmly on the switching drive division of switching the driving source, initial stopper can with switch the drive division butt, the termination stopper can with the shell butt of switching the driving source.

Further, the trimming transmission assembly further comprises a second return spring which is sleeved on the trimming driving portion and the first connecting rod, a limiting flange is arranged on the first connecting rod, and two ends of the second return spring are respectively abutted to a shell and the limiting flange of the trimming driving source.

The invention further provides another thread cutting mechanism which comprises a thread cutting tool apron, a thread hooking plate with a thread hooking part and a cutting knife with a thread cutting tool bit, wherein the thread hooking plate and the cutting knife are movably arranged on the thread cutting tool apron, the thread hooking plate and the cutting knife can move together towards the direction close to or far away from a machine needle in a sewing machine, and the thread hooking plate can move towards the direction close to or far away from the machine needle in the sewing machine relative to the cutting knife; when the thread is cut, the thread hooking plate firstly moves towards the direction close to the needle relative to the cutting knife, so that a thread hooking groove is formed between the thread hooking part of the thread hooking plate and the thread cutting head of the cutting knife; then the thread hooking plate and the cutting knife move together towards the direction close to the needle, so that the thread hooking groove allows the entering of the thread; then the thread hooking plate moves relative to the cutting knife in a direction far away from the needle and close to the cutting knife, and a thread cutting tool bit of the cutting knife cuts off the thread; and then the thread hooking plate and the cutting knife move and reset together in the direction far away from the needle.

Further, the cutting knife is an ultrasonic cutting knife or an electric heating knife.

The invention also provides a sewing machine, wherein the thread cutting mechanism is arranged in the sewing machine.

As described above, the thread trimming mechanism and the sewing machine according to the present invention have the following advantageous effects:

in this application, design into movablely with stationary knife or cutting knife for move the interlock position of sword cutting edge and stationary knife cutting edge when trimming, or the tangent line tool bit on the cutting knife is close to more in the eedle, this application can carry out the trimming in the position department that is close to the eedle center more promptly, thereby it is shorter to guarantee to remain the end of a thread on the sewing material after the trimming, realizes the trimming effect of stub end.

Drawings

Fig. 1 is a schematic structural diagram of a thread trimming mechanism in the prior art.

Fig. 2 to 4 are schematic structural views of the thread trimming mechanism according to the present application, in which fig. 4 omits a sewing machine bottom plate and a knife group mounting plate.

Fig. 5 is a schematic view of the connection between the movable knife, the fixed knife, the pressing sheet and the transmission fork in the present application.

Fig. 6 is a schematic structural view of the movable blade in the present application.

Fig. 7 is a schematic structural diagram of a driving cam in the present application.

Fig. 8 is a schematic view of the connection between the drive cam and the drive shaft in the present application.

Fig. 9 is a schematic structural diagram of a switching driving assembly according to the present application.

Fig. 10 is a schematic view of the connection between the trimming driving source, the first link and the second return spring in the present application.

Fig. 11 to 13 are schematic diagrams illustrating the operation of the thread trimmer mechanism trimming the upper thread and the lower thread after the sewing operation is completed.

Fig. 14 to 17 are schematic diagrams illustrating the operation of the thread trimming mechanism in the present application for trimming the thread end of the upper thread at the time of starting sewing.

Description of the element reference numerals

1 thread trimming cutter group

11 fixed knife

12 moving knife

121 move sword cutting edge

122 hook part

123 first pushing part

124 second pushing part

13 trimming knife holder

131 first sliding chute

14 collude line groove

15 tabletting

151 clamping part

16-axis position screw

17 first limit stop block

18 second limit stop

19 reset torsion spring

110 first limit projection

111 second limit projection

112 second sliding chute

113 knife group mounting plate

2 trimming driving source

21 trimming driving part

3 trimming transmission assembly

31 drive pin

32 transmission shifting fork

321 third chute

33 first link

331 limiting flange

34 drive shaft

35 drive crank

351 crank arm part with hook line

352 switching crank arm

36 first driving crank

37 second link

38 second driving crank

39 third connecting rod

310 driving support

311 second return spring

4 time sequence control cam

41 trimming cam part

411 first highest reset point

412 first lowest trimming starting point

413 first arc segment

414 second arc segment

42 anti-nest cam part

421 second highest reset point

422 second lowest trimming starting point

423 third arc segment

424 fourth arc segment

5 switching drive assembly

51 mounting substrate

511 limit ear plate part

512 guide groove

52 switching drive source

521 switching drive unit

53 switching driving swing arm

54 knock pin

55 first return spring

56 initial stopper

57 end stop block

6 sliding pin

7 ball

8 shock-absorbing cap

91 machine needle

92 lower shaft

93 bottom plate

101 facial line

102 bottom line

103 upper thread end

Detailed Description

The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will become apparent to those skilled in the art from the present disclosure.

It should be understood that the structures, proportions, and dimensions shown in the drawings and described herein are for illustrative purposes only and are not intended to limit the scope of the present invention, which is defined by the claims, but rather by the claims. In addition, the terms such as "upper", "lower", "left", "right", "middle" and "one" used in the present specification are for convenience of description only and are not intended to limit the scope of the present invention, and changes or modifications of the relative relationship thereof may be made without substantial technical changes and modifications.

The present invention relates to a sewing machine, and more particularly, to a thread trimming mechanism in a sewing machine for trimming a thread; namely: the thread cutting mechanism is used for cutting the thread (the upper thread 101 and the bottom thread 102) at the end of sewing, and the thread cutting mechanism is used for cutting the thread (the upper thread head 103) at the beginning of sewing. For convenience of description, in the following examples, the directions are defined as follows: defining the length direction of the sewing machine as a left-right direction, wherein the direction towards the head of the sewing machine is a left direction, and the direction towards the tail of the sewing machine is a right direction, so that the left-right direction is the axial direction of the middle lower shaft 92 of the sewing machine at the same time; defining the width direction of the sewing machine as the front-back direction, and setting the direction of cloth moving driven by a feed dog in the sewing machine as the front direction during sewing; the height direction of the sewing machine is defined as the up-down direction.

As shown in fig. 2 to 6, the thread cutting mechanism according to the present application includes a stationary knife 11 having a stationary knife edge, a movable knife 12 having a movable knife edge 121, and a thread cutting blade holder 13 fixed to a bottom plate 93 of the sewing machine, both the stationary knife 11 and the movable knife 12 are movably mounted on the thread cutting blade holder 13, the stationary knife 11 and the movable knife 12 can move together in a direction approaching or separating from a needle 91 in the sewing machine, the movable knife 12 can move relative to the stationary knife 11 in a direction approaching or separating from the needle 91 in the sewing machine, and the movable knife 12 has a hook portion 122 on a side of the movable knife edge 121 away from the needle 91. When cutting the thread, the movable knife 12 moves towards the direction close to the needle 91 relative to the fixed knife 11, and the fixed knife 11 does not move, so that a thread hooking groove 14 is formed between the thread hooking part 122 of the movable knife 12 and the fixed knife 11, but the thread hooking groove 14 is not arranged on the lower side of the needle 91; then the movable knife 12 and the fixed knife 11 move together towards the direction close to the needle 91, as shown in fig. 11, the thread hooking groove 14 is positioned at the lower side of the needle 91, and a thread is allowed to enter the thread hooking groove 14; then the movable knife 12 moves relative to the fixed knife 11 in the direction far away from the needle 91, and the fixed knife 11 does not move until the movable knife edge 121 is meshed with the fixed knife edge to cut off the suture in the thread hooking slot 14; finally, the movable knife 12 and the fixed knife 11 move together in a direction away from the needle 91 and return to the original position. In this application, design into movablely with stationary knife 11 for move the interlock position of sword cutting edge 121 and stationary knife cutting edge when the trimming and be close to more in eedle 91, this application can carry out the trimming in the position department that is close to eedle 91 center more promptly, thereby it is shorter to guarantee to remain the end of a thread on the sewing material after the trimming, realizes the trimming effect of stub end.

In the thread trimming mechanism, the fixed knife 11, the movable knife 12 and the thread trimming knife holder 13 form a thread trimming knife group 1 of the thread trimming mechanism. Further, as shown in fig. 2 to 5, the thread trimmer 1 further has a cutter set mounting plate 113, the cutter set mounting plate 113 is fixed to the bottom plate 93 of the sewing machine and is flush with the bottom plate 93, the thread trimmer holder 13 is fixed to a lower end surface of the cutter set mounting plate 113, and both the fixed cutter 11 and the movable cutter 12 are movably mounted on an upper end surface of the thread trimmer holder 13, so that the fixed cutter 11 and the movable cutter 12 are movably enclosed between the thread trimmer holder 13 and the cutter set mounting plate 113. Preferably, in this embodiment, the fixed knife 11 and the movable knife 12 move in a straight line in the left-right direction, and move in the direction approaching the needle 91 when moving in the right direction, and move in the direction away from the needle 91 when moving in the left direction; in the initial state, the fixed knife 11 and the movable knife 12 are both positioned on the left side of the needle 91; when the trimming is taken out, the movable knife 12 only moves rightwards and extends out, and a wire hooking groove 14 is formed between the movable knife 12 and the fixed knife 11; then, the movable blade 12 and the fixed blade 11 move together rightward, and the thread hooking groove 14 moves rightward to the lower side of the needle 91.

The thread trimming mechanism is used for trimming the upper thread 101 and the bottom thread 102 after sewing is finished, and trimming the thread head 103 of the upper thread during sewing; in order to ensure that the sewing machine cuts the upper thread end 103 after at least completing the thread locking of the second needle when starting sewing, as shown in fig. 4 and 5, the thread cutting knife group 1 in the thread cutting mechanism further comprises a pressing sheet 15 movably mounted on the thread cutting knife seat 13 and capable of moving along with the fixed knife 11, the pressing sheet 15, the fixed knife 11 and the movable knife 12 are sequentially arranged from top to bottom, the right end of the pressing sheet 15 facing the needle 91 is provided with a clamping part 151 positioned between the cutting edge of the fixed knife and the needle 91, so the clamping part 151 at the right end of the pressing sheet 15 is positioned at the right side of the cutting edge of the fixed knife at the right end of the fixed knife 11. When the upper thread end 103 is trimmed, the moving knife 12, the fixed knife 11 and the pressing sheet 15 are operated in the following sequence: the movable knife 12 moves to the right and extends out, a line hooking groove 14 is formed between the movable knife 12 and the fixed knife 11, and at the moment, the movable knife 12 is still positioned at the left side of the needle 91; then, the movable knife 12, the fixed knife 11 and the pressing sheet 15 move rightwards together, so that the thread hooking groove 14 is positioned at the lower side of the needle 91, as shown in fig. 14; the upper thread end 103 at one end of the needle 91 enters the thread hooking groove 14, as shown in fig. 14; when the needle 91 drives the upper thread end 103 to pierce a needle in the thread hooking groove 14 and then the needle 91 moves back, the movable blade 12 moves leftwards to drive the upper thread end 103 in the thread hooking groove 14 to move leftwards together until the clamping part 151 of the pressing sheet 15 and the movable blade 12 clamp the upper thread end 103, and at the moment, the movable blade edge 121 on the movable blade 12 is not engaged with the fixed blade edge on the fixed blade 11, so that the upper thread end 103 is not cut off but clamped between the pressing sheet 15 and the movable blade 12, as shown in fig. 15; then, after the sewing machine finishes at least the second needle thread locking, the movable knife 12 drives the upper thread end 103 in the thread hooking slot 14 to move leftwards continuously until the movable knife blade 121 and the fixed knife blade are engaged to cut off the upper thread end 103, as shown in fig. 16; finally, the movable knife 12, the fixed knife 11 and the pressing sheet 15 move leftwards together to be reset.

As shown in fig. 4 and 5, the thread trimmer cutter set 1 further includes an axial position screw 16 fixed to the thread trimmer cutter holder 13 and extending up and down, a first limit stop block 17 having a right end hinged to the thread trimmer cutter holder 13 through a pin extending up and down, a second limit stop block 18 having a left end hinged to the thread trimmer cutter holder 13 through a pin extending up and down, and a reset torsion spring 19 sleeved on the axial position screw 16, wherein two ends of the reset torsion spring 19 are respectively connected to the first limit stop block 17 and the second limit stop block 18; meanwhile, the right end of the first limit stop block 17 and the left end of the second limit stop block 18 are both positioned between the trimming tool holder 13 and the shaft position screw 16, so that the shaft position screw 16 simultaneously plays a role in axial limit for the first limit stop block 17 and the second limit stop block 18; the left ends of the fixed knife 11 and the pressing plate 15 are both provided with a first limit protruding part 110, the right ends of the fixed knife 11 and the pressing plate 15 are both provided with a second limit protruding part 111, and the first limit protruding part 110 and the second limit protruding part 111 are oppositely arranged along the moving direction of the fixed knife 11. In the initial state, when the fixed knife 11 and the pressing sheet 15 do not move rightwards, the fixed knife 11 and the pressing sheet 15 are located at the knife return limit position, and at the time, the second limit stop block 18 abuts against the second limit protruding part 111 at the right end of the fixed knife 11 and the pressing sheet 15, so that the limiting effect of limiting the fixed knife 11 and the pressing sheet 15 to move rightwards is achieved; when the wire is cut, after the fixed knife 11 and the pressing sheet 15 move rightwards, the fixed knife 11 and the pressing sheet 15 are located at the knife-out limit position, at this time, the first limit stop block 17 abuts against the first limit protruding part 110 at the left end of the fixed knife 11 and the pressing sheet 15, and the limiting effect of limiting the left movement of the fixed knife 11 and the pressing sheet 15 is achieved. In addition, as shown in fig. 6, the movable blade 12 has a first pushing portion 123 and a second pushing portion 124, and the first pushing portion 123 and the second pushing portion 124 are both inclined portions extending obliquely, wherein the left end of the first pushing portion 123 extends obliquely to the left rear, and the right end of the second pushing portion 124 extends obliquely to the right rear. In the process that the movable knife 12 moves rightwards, the second pushing part 124 on the movable knife 12 pushes away the second limit stop block 18, so that the second limit stop block 18, the fixed knife 11 and the second limit protruding part 111 at the right end of the pressing sheet 15 can allow the fixed knife 11 and the pressing sheet 15 to move rightwards; in the process that the movable blade 12 moves leftwards, the first pushing part 123 on the movable blade 12 pushes away the first limit stop block 17, so that the first limit stop block 17, the fixed blade 11 and the first limit protruding part 110 at the left end of the pressing piece 15 can allow the fixed blade 11 and the pressing piece 15 to move leftwards.

Further, the fixed blade 11 and the pressing piece 15 are moved in the left-right direction and driven by the movable blade 12; specifically, as shown in fig. 4 and 5, the thread trimming mechanism further includes a thread trimming driving source 2 and a thread trimming transmission assembly 3, the thread trimming driving source 2 is connected to the movable knife 12 through the thread trimming transmission assembly 3, the movable knife 12 is driven to move horizontally in the left-right direction, and the movable knife 12 can drive the fixed knife 11 and the pressing piece 15 to move horizontally together. The output end of the trimming transmission component 3 is provided with a transmission shifting fork 32 which can swing, and the transmission shifting fork 32 is hinged with the movable knife 12 through a transmission pin 31 which extends up and down; the upper end surface of the trimming knife holder 13 is provided with a first sliding chute 131 which extends left and right along the moving direction of the movable knife 12, the fixed knife 11 and the pressing sheet 15 are both provided with a second sliding chute 112 which extends left and right along the moving direction of the movable knife 12, and the length of the first sliding chute 131 is greater than that of the second sliding chute 112; the end of the transmission fork 32 is provided with a third sliding chute 321; the transmission pin 31 is respectively matched with the first sliding chute 131 of the trimming knife seat 13, the second sliding chutes 112 of the fixed knife 11 and the pressing plate 15, and the third sliding chute 321 of the transmission shifting fork 32; meanwhile, the movable blade 12, the fixed blade 11 and the pressing piece 15 are movably installed in the first sliding slot 131 of the trimming blade holder 13. In the initial state, the left end of the first sliding chute 131 and the left end of the second sliding chute 112 are aligned up and down, and the driving pin 31 is located at the left ends of the first sliding chute 131 and the second sliding chute 112; when the trimming driving source 2 drives the transmission shifting fork 32 at the tail end of the trimming transmission assembly 3 to swing rightwards, the transmission shifting fork 32 drives the movable knife 12 to move rightwards through the transmission pin 31, at first, the movable knife 12 moves rightwards in the second sliding groove 112 of the fixed knife 11 and the pressing sheet 15, and the fixed knife 11 and the pressing sheet 15 do not move; when the movable knife 12 moves to the right end of the second sliding chute 112, the movable knife 12 continues to move rightwards, and the movable knife 12 drives the fixed knife 11 and the pressing sheet 15 to move rightwards together until the movable knife 12, the fixed knife 11 and the pressing sheet 15 all move rightwards to the respective knife-out limit positions. Similarly, when the trimming driving source 2 drives the transmission fork 32 at the end of the trimming transmission assembly 3 to swing leftwards, the transmission fork 32 drives the moving blade 12 to move leftwards through the transmission pin 31, and initially, the moving blade 12 moves leftwards in the second sliding grooves 112 of the fixed blade 11 and the pressing piece 15, and the fixed blade 11 and the pressing piece 15 do not move; when the movable knife 12 moves to the left end of the second sliding chute 112, the movable knife 12 continues to move leftward, and the movable knife 12 drives the fixed knife 11 and the pressing sheet 15 to move leftward together until the movable knife 12, the fixed knife 11 and the pressing sheet 15 all move leftward to the respective knife-back limit positions and are reset respectively.

The following description will be given of a preferred embodiment of the thread trimming drive assembly 3.

As shown in fig. 3, 4 and 8, the thread cutting transmission assembly 3 includes a first connecting rod 33, a driving shaft 34 parallel to the lower shaft 92 of the sewing machine, a driving crank 35 and a first transmission crank 36 fixed on the driving shaft 34, a second connecting rod 37, a second transmission crank 38, a third connecting rod 39, a transmission fork 32, and a transmission bracket 310 fixed on the bottom plate 93 of the sewing machine, the thread cutting driving source 2 has a thread cutting driving portion 21 capable of extending back and forth, a thread hooking crank arm portion 351 extends from the driving crank 35, two ends of the first connecting rod 33 are respectively hinged to the thread cutting driving portion 21 and the thread hooking crank arm portion, two ends of the second connecting rod 37 are respectively hinged to the first transmission crank 36 and the second transmission crank 38, two ends of the third connecting rod 39 are respectively hinged to the second transmission crank 38 and the transmission fork 32, the second transmission crank 38 and the transmission fork 32 are both hinged to the transmission bracket 310, the second transmission crank 38 and the transmission bracket 310 constitute a fixed swing fulcrum of the second transmission crank 38 O1, the hinge point of the transmission fork 32 and the transmission bracket 310 forms a fixed swing fulcrum O2 of the transmission fork 32, and the transmission fork 32 and the movable blade 12 are connected through the transmission pin 31. The trimming driving source 2 can select an electromagnet, a cylinder, a linear motor and the like; in this embodiment, the trimming driving source 2 is an electromagnet. The thread cutting driving source 2 is connected with a control system, and the control system can be an electric control module in the sewing machine; in the initial state, the control system controls the thread cutting driving source 2 to be in the power-off state, and the thread cutting driving part 21 of the thread cutting driving source 2 is in the forward extending state; when the upper thread end 103 is automatically trimmed after sewing and when the upper thread is automatically trimmed after sewing, the control system controls the thread cutting driving source 2 to be electrified, the thread cutting driving part 21 of the thread cutting driving source 2 moves backwards, the driving shaft 34 is driven to swing through the first connecting rod 33 and the first transmission crank 36, the driving shaft 34 drives the transmission shifting fork 32 to swing rightwards through the first transmission crank 36, the second connecting rod 37, the second transmission crank 38 and the third connecting rod 39, and further the movable knife 12 is driven to move rightwards in a direction close to the machine needle 91.

In order to make the action time sequence of the movable knife 12 when trimming the thread after sewing is finished different from the action time sequence of the movable knife 12 when starting to trim the thread end 103 of the upper thread, namely: in order to realize that the movable knife 12 and the pressing sheet 15 can clamp the upper thread end 103 before the second needle locking needle of the sewing machine is finished when starting sewing, but the upper thread end 103 is not cut off, as shown in fig. 3, 4, 7 and 8, the thread cutting transmission assembly 3 further comprises a switching crank arm part 352 extending from the driving crank 35, a sliding pin 6 parallel to the driving shaft 34, a ball 7 rotatably mounted at the left end of the sliding pin 6, a thread cutting cam part 41 and an anti-bird nest cam part 42 which are both fixed on the lower shaft 92 and arranged left and right, and a switching driving assembly 5 for driving the sliding pin 6 to move left and right, wherein the sliding pin 6 is mounted in the outer end of the switching crank arm part 352 in a left-right movement manner, and the switching driving assembly 5 drives the sliding pin 6 to move axially so that the ball 7 is abutted against the outer peripheral surface of the thread cutting cam part 41 or the outer peripheral surface of the anti-bird nest cam part. When trimming after sewing, the switching drive unit 5 makes the ball 7 fixed at the left end of the slide pin 6 positioned on the outer peripheral side of the trimming cam portion 41, and the ball 7 is in contact with the outer peripheral surface of the trimming cam portion 41; in the thread cutting process, the lower shaft 92 drives the thread cutting cam part 41 to rotate, the switching crank arm part 352 is driven to rotate by an angle through the diameter-changing characteristic of the outer peripheral surface of the thread cutting cam part 41, and the movable knife 12 is moved rightwards to the knife-out limit position and the movable knife 12 is moved leftwards to the knife-back limit position by combining with the thread cutting driving source 2. When starting sewing, the switching drive assembly 5 makes the ball 7 fixed at the left end of the sliding pin 6 be positioned at the outer periphery side of the anti-bird-nest cam part 42 first, and then the ball 7 is contacted with the outer periphery side of the anti-bird-nest cam part 42; in the process of sewing, the lower shaft 92 drives the bird's nest prevention cam part 42 to rotate, the switching crank arm part 352 is driven to rotate by an angle through the diameter-changing characteristic of the outer peripheral surface of the bird's nest prevention cam part 42, the movable knife 12 is moved rightwards to the knife-out limit position of the movable knife 12 by combining with the thread trimming driving source 2, and the movable knife 12 is moved leftwards until the movable knife 12 and the pressing sheet 15 clamp the upper thread end 103; after the sewing machine finishes at least the second needle thread locking, the driving assembly 5 is switched to position the ball 7 at the outer periphery of the thread trimming cam portion 41, and the ball 7 is abutted to the outer periphery of the thread trimming cam portion 41, so that the movable knife 12 moves leftwards to the knife return limit position.

The preferred embodiments of the trimming cam portion 41 and the anti-nest cam portion 42 are: as shown in fig. 7, the trimming cam portion 41 and the bird nest prevention cam portion 42 are integrated into one timing control cam 4. The outer peripheral surface of the trimming cam portion 41 has a first highest reset point 411 and a first lowest trimming start point 412, the outer peripheral surface of the anti-bird nest cam portion 42 has a second highest reset point 421 and a second lowest trimming start point 422, the radius of the first highest reset point 411 is larger than that of the second highest reset point 421, and the radius of the first lowest trimming start point 412 is equal to that of the second lowest trimming start point 422. When the ball 7 abuts against the first highest returning point 411, as shown in fig. 13 or 17, the moving blade edge 121 engages with the fixed blade edge; when the ball 7 abuts against the second highest returning point 421, as shown in fig. 15, the clamping portion 151 of the pressing piece 15 and the movable blade 12 are clamped, but the movable blade edge 121 and the fixed blade edge are not engaged; when the ball 7 abuts against the first lowest trimming starting point 412 or the second lowest trimming starting point 422, the movable blade 12 moves to a blade-out limit position in a direction approaching the needle 91, as shown in fig. 11 or fig. 14, the thread hooking groove 14 formed between the movable blade 12 and the fixed blade 11 is located at the lower side of the needle 91, and the upper thread 101 and the lower thread 102 are allowed to enter or the upper thread head 103 is allowed to enter in the thread hooking groove 14. In other embodiments, the trimming cam portion 41 and the anti-bird nest cam portion 42 may be two independent cams, and the installation positions may be interchanged.

Further, as shown in fig. 7, two arc sections of the outer peripheral surface of the trimming cam portion 41 between the first highest resetting point 411 and the first lowest trimming starting point 412 are a first arc section 413 and a second arc section 414 in sequence in the direction in which the outer peripheral surface of the trimming cam portion 41 contacts the ball 7, the radius of the first arc section 413 is gradually reduced from the radius value at the first highest resetting point 411 to the radius value at the first lowest trimming starting point 412, and the radius of the second arc section 414 is gradually increased from the radius value at the first lowest trimming starting point 412 to the radius value at the first highest resetting point 411. Therefore, the ball 7 is firstly abutted against the first highest reset point 411 of the trimming cam portion 41, and as the lower shaft 92 drives the trimming cam portion 41 to rotate, the ball 7 is sequentially contacted with the first circular arc segment 413, the first lowest trimming starting point 412 and the second circular arc segment 414, and is finally abutted against the first highest reset point 411.

Further, as shown in fig. 8, two arc sections of the outer peripheral surface of the anti-bird nest cam portion 42 between the second highest reset point 421 and the second lowest trimming line starting point 422 are a third arc section 423 and a fourth arc section 424 in sequence along the direction in which the outer peripheral surface of the anti-bird nest cam portion 42 contacts the ball 7, the radius of the third arc section 423 is gradually reduced from the radius value at the second highest reset point 421 to the radius value at the second lowest trimming line starting point 422, and the radius of the fourth arc section 424 is gradually increased from the radius value at the second lowest trimming line starting point 422 to the radius value at the second highest reset point 421. Meanwhile, the anti-nest cam portion 42 has a stop segment with an equal radius at the second lowest shear line starting point 422. Therefore, the ball 7 is firstly abutted against the second highest reset point 421 of the anti-bird nest cam portion 42, and as the lower shaft 92 drives the anti-bird nest cam portion 42 to rotate, the ball 7 is sequentially contacted with the third arc segment 423, the second lowest shear line starting point 422 (i.e. the starting point of the stop segment) and the fourth arc segment 424, and is finally abutted against the second highest reset point 421.

As shown in fig. 4, 8 and 9, the switching drive assembly 5 includes a mounting base plate 51 fixed to the lower end surface of a middle bottom plate 93 of the sewing machine, a switching drive source 52 fixed to the mounting base plate 51, a switching drive swing arm 53 extending forward and backward, a knock pin 54 extending upward and downward, a damper cap 8 fixed to the right end of the slide pin 6, and a first return spring 55 fitted around the slide pin 6, wherein the front end of the switching drive swing arm 53 is hinged to the mounting base plate 51, a fixed swing fulcrum O3 constituting the switching drive swing arm 53, the switching drive source 52 has a switching drive portion 521 capable of extending leftward and rightward along the axial direction of the slide pin 6, the lower end of the knock pin 54 is fixedly connected to the switching drive portion 521, the knock pin 54 is located on the right side of the switching drive swing arm 53, the middle portion of the knock pin 54 is capable of abutting against the right side wall of the switching drive swing arm 53, the rear end of the switching, the left and right ends of the first return spring 55 are respectively in contact with the switching crank arm portion 352 and the damper cap 8. The switching drive source 52 can be an electromagnet, an air cylinder, a linear motor or the like, and the switching drive source 52 is connected with a control system; in this embodiment, the switching drive source 52 is an electromagnet. When the control system controls the switching drive source 52 to be in the power-off state, the switching drive unit 521 of the switching drive source 52 is in the state of extending rightward, and at this time, the first return spring 55 is not compressed, and the ball 7 at the left end of the slide pin 6 is located on the outer peripheral side of the anti-bird nest cam portion 42. When the control system controls the switching driving source 52 to be in the power-on state, the switching driving part 521 of the switching driving source 52 retracts leftwards, the switching driving part 521 drives the ejector pin 54 to move leftwards together, the switching driving swing arm 53 is pushed by the ejector pin 54 to swing leftwards, the sliding pin 6 is pushed by the pushing part at the rear end of the switching driving swing arm 53 to move leftwards, at this time, the first return spring 55 is compressed, and the ball 7 at the left end of the sliding pin 6 is positioned on the outer peripheral side of the trimming cam part 41; after the trimming is completed, the control system controls the switching drive source 52 to be powered off, the switching drive unit 521 of the switching drive source 52 extends and returns to the right, the slide pin 6 is moved to the right and returns to the right under the action of the first return spring 55, and the switching drive swing arm 53 swings and returns to the right, at this time, the ball 7 at the left end of the slide pin 6 is positioned on the outer periphery side of the bird's nest prevention cam portion 42.

Further, as shown in fig. 9, the mounting board 51 is provided with a guide groove 512 extending in the left-right direction of the movement of the knock pin 54, and the top end of the knock pin 54 is inserted into the guide groove 512 and contacts with the groove wall of the guide groove 512, thereby improving the stability of the movement of the knock pin 54 in the left-right direction. A limit ear plate part 511 extending upwards is arranged at the right end of the mounting substrate 51, an initial limit block 56 positioned at the right side of the top pin 54 is fixed on the limit ear plate part 511, and a termination limit block 57 positioned at the left side of the top pin 54 is fixed on the switching driving part 521 of the switching driving source 52; when the switching driving source 52 is powered off, the initial limit block 56 is abutted against the right end of the switching driving part 521 to play a limiting role; when the switching drive source 52 is energized, the end stopper 57 abuts against the outer case of the switching drive source 52, and a stopper function is performed.

As shown in fig. 10, the trimming transmission assembly 3 further includes a second return spring 311 sleeved on the trimming driving portion 21 and the first connecting rod 33, the first connecting rod 33 is provided with a limit flange 331, and two ends of the second return spring 311 are respectively abutted against the housing of the trimming driving source 2 and the limit flange 331. After the control system controls the cutting line driving source 2 to be powered off, the second return spring 311 and the first highest return point 411 on the outer peripheral surface of the cutting line cam part 41 enable the movable knife 12 to move leftwards to the knife return limit position, and in the process, the movable knife edge 121 is meshed with the fixed knife edge; alternatively, the movable blade 12 is moved leftward to be clamped with the pressing piece 15 by the second return spring 311 and the second highest return point 421 on the outer peripheral surface of the anti-bird nest cam portion 42.

The thread trimming mechanism with the structure works according to the following principle:

in an initial state, that is, in a normal sewing state of the sewing machine, the trimming drive source 2 and the switching drive source 52 are both in a power-off state, and the balls 7 are stabilized at an initial position and positioned on the outer peripheral side of the anti-bird nest cam portion 42 by the first return spring 55, but the balls 7 are not in contact with the outer peripheral surface of the anti-bird nest cam portion 42; the movable knife 12 is stabilized at the initial position under the action of the second return spring 311, the driving pin 31 in the movable knife 12 abuts against the left end of the first sliding chute 131 in the thread trimming knife seat 13 and the left ends of the second sliding chutes 112 in the fixed knife 11 and the pressing sheet 15, and the movable knife 12, the fixed knife 11 and the pressing sheet 15 are all located at the respective back-cutting limit positions, are all retracted in the thread trimming knife seat 13 and are all located at the left side of the needle 91, as shown in fig. 13; the sewing machine sews normally.

The automatic thread trimming method after sewing is as follows: when the sewing machine finishes sewing and cuts thread, a control system of the sewing machine receives a thread cutting signal, the control system firstly controls the switching drive source 52 to be electrified, so that the slide pin 6 drives the ball 7 to move leftwards, and the ball 7 is positioned on the outer peripheral side of the thread cutting cam part 41 but is not in contact with the outer peripheral side of the thread cutting cam part 41. Then, the control system controls the power on of the thread cutting driving source 2, the thread cutting driving source 2 drives the driving shaft 34 to rotate through the first connecting rod 33 and the driving crank 35, and the sliding pin 6 installed in the driving crank 35 carries the ball 7 to contact the outer peripheral surface of the thread cutting cam part 41; the timing control cam 4 and the rotary hook rotate together with the lower shaft 92, and the upper thread 101 is divided into a figure of "eight" below the needle 91 as shown in fig. 11 by the rotation of the rotary hook; the ball 7 relatively slides along the outer peripheral surface of the trimming cam portion 41 in contact, entering the first lowest trimming start point 412 on the trimming cam portion 41; in the process, the driving shaft 34 further causes the transmission fork 32 to swing to the right around the fixed swing fulcrum O2 through the first transmission crank 36, the second connecting rod 37, the second transmission crank 38 and the third connecting rod 39, and then the movable knife 12 is driven to move towards the right in the direction approaching the needle 91, the second pushing part 124 on the movable knife 12 pushes the second limit stop block 18 away, at the same time, the driving pin 31 moves to the right end of the second sliding slot 112 on the fixed knife 11 and the pressing piece 15, and then the movable knife 12 carries the fixed knife 11 and the pressing piece 15 together to move rightwards in the direction close to the needle 91 until the three move to the respective knife-out limit positions, at this time, the hook groove 14 formed between the hook portions 122 of the fixed blade 11 and the movable blade 12 is located right below the needle 91, the upper thread 101 and the lower thread 102 enter the hook groove 14, and the first limit stopper 17 abuts against the fixed knife 11 and the first limit projection 110 on the pressing piece 15 by the return torsion spring 19. Then, the control system controls the power-off of the trimming driving source 2, under the combined action of the second return spring 311 and the first highest return point 411 on the trimming cam portion 41, the transmission shift fork 32 swings and returns to the left around the fixed swing fulcrum O2, so as to drive the movable knife 12 to move leftward in the direction away from the needle 91 until the movable knife blade 121 is engaged with the fixed knife blade, and the hook portion 122 on the movable knife 12 pulls the bottom thread 102 in the hook slot 14 and the upper thread 101 together to the fixed knife 11 to be cut off, as shown in fig. 12; the movable knife 12 continues to move leftwards, the first pushing part 123 on the movable knife 12 pushes away the first limit stop block 17, meanwhile, the driving pin 31 moves to the left end of the second sliding slot 112 on the fixed knife 11 and the pressing sheet 15, then the movable knife 12 carries the fixed knife 11 and the pressing sheet 15 together to move leftwards away from the machine needle 91 until the three move to the respective knife-back limit positions and are respectively reset, as shown in fig. 13, and the second limit stop block 18 abuts against the second limit projection 111 on the fixed knife 11 and the pressing sheet 15 under the action of the reset torsion spring 19. Finally, the control system controls the switching driving source 52 to be powered off, the sliding pin 6 moves rightwards to reset under the action of the first reset spring 55, the ball 7 is positioned on the outer periphery side of the bird nest prevention cam part 42, and finally the action of finishing thread trimming after sewing is finished.

When the sewing machine starts up again, the control system controls the thread cutting driving source 2 to be electrified while the sewing machine is started, the thread cutting driving source 2 drives the driving shaft 34 to rotate through the first connecting rod 33 and the driving crank 35, the sliding pin 6 arranged in the driving crank 35 drives the ball 7 to contact with the outer peripheral surface of the anti-nest cam part 42, the timing control cam 4 and the rotating shuttle rotate together with the lower shaft 92, and the ball 7 relatively slides along the outer peripheral surface of the anti-nest cam part 42 in a contact manner and enters the second lowest thread cutting starting point 422 on the anti-nest cam part 42; in the process, the driving shaft 34 further drives the transmission fork 32 to swing rightwards around the fixed swing fulcrum O2 through the first transmission crank 36, the second connecting rod 37, the second transmission crank 38 and the third connecting rod 39, so as to drive the movable blade 12 to move rightwards in the direction approaching the needle 91 first, then the second pushing part 124 on the movable blade 12 pushes the second limit stop block 18 open, the transmission pin 31 moves to the right end of the second sliding slot 112 on the fixed blade 11 and the pressing sheet 15, then the movable blade 12 carries the fixed blade 11 and the pressing sheet 15 together to move rightwards in the direction approaching the needle 91 until the three move to the respective knife-out limit positions, at this time, the hook slot 14 formed between the fixed blade 11 and the hook part 122 on the movable blade 12 is located at the right lower side of the needle 91, the needle 91 carries the needle thread 103 to puncture a needle in the hook slot 14 and then the needle 91 moves backwards, as shown in fig. 14, the needle thread 103 enters the hook slot 14, and the first limit stopper 17 abuts against the fixed knife 11 and the first limit projection 110 on the pressing piece 15 by the return torsion spring 19. Then, the control system controls the power-off of the thread trimming driving source 2, under the combined action of the second return spring 311 and the second highest return point 421 on the anti-bird nest cam portion 42, the transmission shifting fork 32 swings around the fixed swing fulcrum O2 to return to the left, so as to drive the movable knife 12 to move a distance to the left in the direction away from the needle 91, at this time, the movable knife blade 121 and the fixed knife blade are not completely engaged, and the pressing sheet 15 and the movable knife 12 are extruded on the surface to clamp the upper thread end 103, as shown in fig. 15. The sewing machine continues to move, after the thread locking of the first stitch length is finished, namely after the thread locking of the second needle is finished, the control system controls the switching driving source 52 to be electrified, so that the sliding pin 6 drives the ball 7 to move leftwards, and the ball 7 enters the outer peripheral side of the thread cutting cam part 41; the ball 7 relatively slides along the outer peripheral surface of the trimming cam portion 41 in a contact manner, so that the movable knife 12 moves leftwards again in a direction away from the needle 91 until the movable knife blade 121 is meshed with the fixed knife blade, and the hook portion 122 on the movable knife 12 pulls the facial suture head 103 to be trimmed in the hook slot 14 leftwards to the fixed knife 11 for cutting, as shown in fig. 16; the movable knife 12 continues to move leftwards, the first pushing part 123 on the movable knife 12 pushes away the first limit stop block 17, meanwhile, the driving pin 31 moves to the left end of the second sliding slot 112 on the fixed knife 11 and the pressing piece 15, then the movable knife 12 carries the fixed knife 11 and the pressing piece 15 together to move leftwards away from the machine needle 91 until the three move to the respective knife-back limit positions and are respectively reset, as shown in fig. 17, and the second limit stop block 18 abuts against the second limit projection 111 on the fixed knife 11 and the pressing piece 15 under the action of the reset torsion spring 19. Finally, the control system controls the switching driving source 52 to be powered off, the sliding pin 6 moves rightwards to reset under the action of the first reset spring 55, the ball 7 is positioned on the outer periphery side of the anti-bird-nest cam portion 42, and finally the action of cutting off the redundant upper thread end 103 during seam starting is finished, so that the seam starting end is cut off, and the thread end is prevented from winding to form a bird-nest thread ball.

Further, the present application also provides another embodiment of a thread trimming mechanism, which is different from the thread trimming mechanism in the above embodiments in that: the pressing sheet 15 is omitted, the movable knife 12 is replaced by a wire hooking plate with a wire hooking part 122, the fixed knife 11 is replaced by a cutting knife with a wire cutting knife head, and the cutting knife is an ultrasonic cutting knife or an electric heating knife; meanwhile, in the timing control cam 4, the radius of the first highest reset point 411 on the trimming cam portion 41 is equal to the radius of the second highest reset point 421 on the anti-bird nest cam portion 42, and the radius of the first lowest trimming starting point 412 on the trimming cam portion 41 is equal to the radius of the second lowest trimming starting point 422 on the anti-bird nest cam portion 42. Therefore, the thread hooking plate and the cutting knife can be mounted on the thread cutting knife seat 13 in a left-right moving mode, the thread hooking plate and the cutting knife can move together towards the direction close to or far away from the needle 91 in the sewing machine, and the thread hooking plate can move towards the direction close to or far away from the needle 91 in the sewing machine relative to the cutting knife. The working principle is as follows:

when the sewing machine finishes sewing and cuts thread, the control system of the sewing machine receives a thread cutting signal, and the control system firstly controls the switching drive source 52 to be electrified, so that the ball 7 is positioned at the outer peripheral side of the thread cutting cam part 41. Then, the control system controls the thread cutting driving source 2 to be electrified, and the slide pin 6 carries the ball 7 to contact the outer peripheral surface of the thread cutting cam part 41; the timing control cam 4 and the rotary hook rotate together with the lower shaft 92, and the ball 7 enters the first lowest trimming starting point 412 on the trimming cam portion 41; in this process, the drive shaft 34 drives the thread hooking plate to move rightward in the direction approaching the needle 91, and then the thread hooking plate moves rightward in the direction approaching the needle 91 together with the cutting knife by the driving pin 31 until the thread hooking plate and the cutting knife move to the respective extreme positions, at this time, the thread hooking groove 14 formed between the cutting knife and the thread hooking portion 122 of the thread hooking plate is located at the right lower side of the needle 91, and the upper thread 101 and the lower thread 102 enter the thread hooking groove 14. Then, the control system controls the power-off of the trimming driving source 2, under the combined action of the second return spring 311 and the first highest return point 411 on the trimming cam part 41, the movable trimming plate moves leftwards in the direction away from the needle 91, the trimming part 122 on the trimming plate pulls the bottom thread 102 and the upper thread 101 in the trimming groove 14 leftwards to the position of the cutting knife, and the cutting knife is powered on and then trimming is realized in an ultrasonic or hot melting mode; the thread hooking plate continues to move leftwards, the thread hooking plate drives the cutting knife to move leftwards together in the direction away from the needle 91 through the transmission pin 31 until the thread hooking plate and the cutting knife move to the respective knife-back limit positions and reset respectively. Finally, the control system controls the switching driving source 52 to be powered off, the sliding pin 6 moves rightwards to reset under the action of the first reset spring 55, the ball 7 is positioned on the outer periphery side of the bird nest prevention cam part 42, and finally the action of finishing thread trimming after sewing is finished.

When the sewing machine starts up again, the control system controls the thread trimming driving source 2 to be electrified when the sewing machine is started, the sliding pin 6 carries the ball 7 to contact the outer peripheral surface of the bird nest prevention cam part 42, the sequential control cam 4 and the rotating shuttle rotate together with the lower shaft 92, and the ball 7 enters the second lowest thread trimming starting point 422 on the bird nest prevention cam part 42; in the process, the drive shaft 34 drives the thread hooking plate to move rightwards in the direction close to the needle 91 firstly, then the thread hooking plate drives the cutting knife to move rightwards in the direction close to the needle 91 together through the transmission pin 31 until the thread hooking plate and the cutting knife move to the respective cutting-out limit positions, at the moment, a thread hooking groove 14 formed between the cutting knife and a thread hooking part 122 on the thread hooking plate is positioned at the right lower side of the needle 91, the needle 91 drives the upper thread head 103 to puncture a needle in the thread hooking groove 14, then the needle 91 moves upwards and lifts, and the upper thread head 103 enters the thread hooking groove 14. Then, the control system controls the thread cutting driving source 2 to be powered off, under the combined action of the second return spring 311 and the second highest return point 421 on the bird nest prevention cam part 42, the first movable thread hooking plate moves leftwards in the direction away from the needle 91, and the thread hooking part 122 on the thread hooking plate pulls the bottom thread 102 and the upper thread 101 in the thread hooking groove 14 to the left to the position of the cutting knife; after the sewing machine finishes the thread locking of the first needle pitch, namely the thread locking of the second needle, the control system controls the cutting knife to be electrified, and the thread cutting is realized by adopting an ultrasonic wave or hot melting mode after the cutting knife is electrified; the thread hooking plate continues to move leftwards, the thread hooking plate drives the cutting knife to move leftwards together in the direction away from the needle 91 through the transmission pin 31 until the thread hooking plate and the cutting knife move to the respective knife-back limit positions and reset respectively, and finally the action of cutting off the redundant thread end 103 of the upper thread is finished when the sewing is started.

In summary, the thread trimming mechanism of the present application has the following advantages: the thread trimming mechanism is arranged below the bottom plate 93, does not occupy the operation space of a machine head, has no limitation caused by the non-universal presser foot and the like, and can realize automatic thread trimming after sewing and bird nest prevention during seam starting; in particular, stationary knife 11 or cutting knife are movable, make move the interlock position of sword cutting edge 121 and stationary knife cutting edge when trimming, or the tangent line tool bit on the cutting knife is close to more in eedle 91, can cut the line in the position department that is close to eedle 91 center more, thereby it is shorter to guarantee to remain the end of a thread on the sewing material after the cutting line, realize the trimming effect of stub end, guarantee the pleasing to the eye of sewing article front end and rear end line trace, reduce the process of trimming the end of a thread, realize high-quality sewing. In addition, when the sewing thread does not need to be trimmed, the movable knife 12 and the fixed knife 11, or the thread hooking plate and the cutting knife are all retracted in the thread trimming knife seat 13 and are all far away from the sewing area of the machine needle 91, so that the thread breakage caused by the winding and unwinding of the thread in the normal sewing process cannot be interfered.

Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims (13)

1. The utility model provides a thread trimming mechanism, is including stationary knife (11) that have the stationary knife cutting edge to and have move sword (12) that move sword cutting edge (121), its characterized in that: the sewing machine further comprises a thread trimming cutter holder (13), the fixed cutter (11) and the movable cutter (12) are movably mounted on the thread trimming cutter holder (13), the fixed cutter (11) and the movable cutter (12) can move together towards the direction close to or away from the needle (91) in the sewing machine, the movable cutter (12) can move towards the direction close to or away from the needle (91) in the sewing machine relative to the fixed cutter (11), and a thread hooking part (122) is arranged on one side, away from the needle (91), of the movable cutter blade (121) of the movable cutter (12); when in thread cutting, the movable knife (12) firstly moves towards the direction close to the needle (91) relative to the fixed knife (11), so that a thread hooking groove (14) is formed between the thread hooking part (122) of the movable knife (12) and the fixed knife (11); then the movable knife (12) and the fixed knife (11) move together towards the direction close to the needle (91) to allow the suture to enter the thread hooking groove (14); then the movable knife (12) moves relative to the fixed knife (11) in the direction far away from the needle (91), so that the cutting edge (121) of the movable knife is meshed with the cutting edge of the fixed knife, and the suture in the thread hooking groove (14) is cut off; then the movable knife (12) and the fixed knife (11) move together in the direction away from the needle (91) and reset;

the thread trimming mechanism further comprises a pressing sheet (15) which is movably arranged on the thread trimming cutter holder (13) and can move along with the fixed cutter (11), the pressing sheet (15), the fixed cutter (11) and the movable cutter (12) are sequentially arranged from top to bottom, and one end, facing the needle (91), of the pressing sheet (15) is provided with a clamping part (151) located between the cutting edge of the fixed cutter and the needle (91); when the upper thread end (103) is sewn and trimmed, the movable knife (12) drives the upper thread end (103) in the thread hooking groove (14) to move relative to the fixed knife (11) in the direction away from the needle (91), so that the clamping part (151) of the pressing sheet (15) and the movable knife (12) clamp the upper thread end (103); after the sewing machine at least completes the second needle thread locking, the movable knife (12) further drives the upper thread end (103) in the thread hooking groove (14) to continue to move towards the direction far away from the machine needle (91) relative to the fixed knife (11) until the cutting edge (121) of the movable knife is occluded with the cutting edge of the fixed knife;

the thread trimming mechanism further comprises an axial position screw (16) fixed on the thread trimming cutter holder (13), a first limit stop block (17) with one end hinged to the thread trimming cutter holder (13), a second limit stop block (18) with one end hinged to the thread trimming cutter holder (13), and a reset torsion spring (19) sleeved on the axial position screw (16), wherein two ends of the reset torsion spring (19) are respectively connected with the first limit stop block (17) and the second limit stop block (18); the fixed knife (11) and the pressing sheet (15) are respectively provided with a first limit protruding part (110) and a second limit protruding part (111) which are oppositely arranged along the moving direction of the fixed knife (11); when the fixed knife (11) and the pressing sheet (15) move to the knife-out limit position in the direction close to the needle (91), the first limit stop block (17) abuts against the first limit protruding part (110) on the fixed knife (11) and the pressing sheet (15); when the fixed knife (11) and the pressing sheet (15) move to the knife-back limit position in the direction away from the needle (91), the second limit stop block (18) abuts against the second limit protruding part (111) on the fixed knife (11) and the pressing sheet (15).

2. The thread trimming mechanism of claim 1, wherein: the movable knife (12) is provided with a first pushing part (123) capable of pushing the first limit stop block (17) to swing and a second pushing part (124) capable of pushing the second limit stop block (18) to swing.

3. The thread trimming mechanism of claim 1, wherein: the wire cutting machine is characterized by further comprising a wire cutting driving source (2) and a wire cutting transmission assembly (3), wherein the wire cutting driving source (2) is connected with the movable knife (12) through the wire cutting transmission assembly (3) and drives the movable knife (12) to move horizontally, and the movable knife (12) can drive the fixed knife (11) and the pressing sheet (15) to move horizontally together.

4. The thread trimming mechanism of claim 3, wherein: the output end of the trimming transmission component (3) is provided with a transmission shifting fork (32) capable of swinging, and the transmission shifting fork (32) is hinged with the movable knife (12) through a transmission pin (31); a first sliding groove (131) extending along the moving direction of the moving blade (12) is formed in the trimming tool apron (13), a second sliding groove (112) extending along the moving direction of the moving blade (12) is formed in both the fixed blade (11) and the pressing sheet (15), and the length of the first sliding groove (131) is greater than that of the second sliding groove (112); the tail end of the transmission shifting fork (32) is provided with a third sliding chute (321); the transmission pin (31) is respectively matched with a first sliding groove (131) of the trimming tool apron (13), a second sliding groove (112) of the fixed knife (11) and the pressing plate (15), and a third sliding groove (321) of the transmission shifting fork (32).

5. The thread trimming mechanism of claim 3, wherein: the thread cutting transmission assembly (3) comprises a first connecting rod (33), a driving shaft (34) parallel to a middle lower shaft (92) of the sewing machine, a driving crank (35) and a first transmission crank (36) which are fixed on the driving shaft (34), a second connecting rod (37), a second transmission crank (38), a third connecting rod (39), a transmission shifting fork (32) and a transmission support (310) fixed on a middle bottom plate (93) of the sewing machine, wherein the thread cutting driving source (2) is provided with a telescopic thread cutting driving part (21), a thread hooking crank arm part (351) extends from the driving crank (35), two ends of the first connecting rod (33) are respectively hinged with the thread cutting driving part (21) and the thread hooking crank arm part (351), two ends of the second connecting rod (37) are respectively hinged with the first transmission crank (36) and the second transmission crank (38), two ends of the third connecting rod (39) are respectively hinged with the second transmission crank (38) and the transmission shifting fork (32), the second transmission crank (38) and the transmission shifting fork (32) are hinged to the transmission bracket (310), and the transmission shifting fork (32) is connected with the movable blade (12).

6. The thread trimming mechanism of claim 5, wherein: the trimming transmission assembly (3) further comprises a switching crank arm part (352) extending from the driving crank (35), a sliding pin (6) parallel to the driving shaft (34), a ball (7) rotatably mounted on the sliding pin (6), a trimming cam part (41) and an anti-bird-nest cam part (42) which are both fixed on the lower shaft (92), and a switching driving assembly (5) for driving the sliding pin (6) to move, wherein the sliding pin (6) is movably mounted in the switching crank arm part (352), and the switching driving assembly (5) drives the sliding pin (6) to move axially so that the ball (7) is abutted against the outer peripheral surface of the trimming cam part (41) or the outer peripheral surface of the anti-bird-nest part (42); when trimming after sewing, the ball (7) is abutted with the outer peripheral surface of the trimming cam part (41); when sewing, the ball (7) is firstly abutted with the outer peripheral surface of the bird nest prevention cam part (42), and after the sewing machine at least completes the second needle thread locking, the ball (7) is abutted with the outer peripheral surface of the thread cutting cam part (41).

7. The thread trimming mechanism of claim 6, wherein: the thread cutting cam part (41) and the bird nest prevention cam part (42) are integrated into a sequential control cam (4).

8. The thread trimming mechanism of claim 6, wherein: the outer peripheral surface of the trimming cam part (41) is provided with a first highest resetting point (411) and a first lowest trimming starting point (412), the outer peripheral surface of the bird's nest prevention cam part (42) is provided with a second highest resetting point (421) and a second lowest trimming starting point (422), the radius of the first highest resetting point (411) is larger than that of the second highest resetting point (421), and the radius of the first lowest trimming starting point (412) is equal to that of the second lowest trimming starting point (422); when the ball (7) is abutted against the first highest reset point (411), the movable cutter blade (121) is meshed with the fixed cutter blade; when the ball (7) is abutted against a second highest reset point (421), the clamping part (151) of the pressing sheet (15) and the movable blade (12) are clamped; when the ball (7) is abutted to the first lowest trimming starting point (412) or the second lowest trimming starting point (422), the movable knife (12) moves to a knife-out limit position in a direction close to the needle (91).

9. The thread trimming mechanism of claim 6, wherein: the switching driving component (5) comprises a mounting base plate (51) fixed on a middle bottom plate (93) of the sewing machine, a switching driving source (52) fixed on the mounting base plate (51), a switching driving swing arm (53) hinged to the mounting base plate (51), a top pin (54) extending up and down, a damping cap (8) fixed at the end part of the sliding pin (6) and a first return spring (55) sleeved on the sliding pin (6), the switching drive source (52) has a switching drive unit (521) that can expand and contract in the axial direction of the slide pin (6), the ejector pin (54) is fixedly connected with a switching driving part (521), the ejector pin (54) can be abutted against a switching driving swing arm (53), the switching driving swing arm (53) is provided with a pushing part which can be abutted with the damping cap (8), and two ends of the first return spring (55) are respectively abutted against the switching crank arm part (352) and the damping cap (8).

10. The thread trimming mechanism of claim 9, wherein: the mounting base plate (51) is provided with a guide groove (512) extending along the moving direction of the top pin (54), and the end part of the top pin (54) is arranged in the guide groove (512) in a penetrating way and is contacted with the groove wall of the guide groove (512).

11. The thread trimming mechanism of claim 9, wherein: the mounting substrate (51) is provided with a limiting lug plate part (511) extending upwards, an initial limiting block (56) located on one side of the top pin (54) is fixed on the limiting lug plate part (511), a termination limiting block (57) located on the other side of the top pin (54) is fixed on a switching driving part (521) of the switching driving source (52), the initial limiting block (56) can be abutted against the switching driving part (521), and the termination limiting block (57) can be abutted against a shell of the switching driving source (52).

12. The thread trimming mechanism of claim 5, wherein: the trimming transmission assembly (3) further comprises a second reset spring (311) which is sleeved on the trimming driving part (21) and the first connecting rod (33), a limiting flange (331) is arranged on the first connecting rod (33), and two ends of the second reset spring (311) are respectively connected with a shell of the trimming driving source (2) and the limiting flange (331) in a butting mode.

13. A sewing machine characterized by: the sewing machine is provided with the thread trimming mechanism of any one of claims 1 to 12.

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