CN106894175B

CN106894175B - automatic thread trimming mechanism of sewing machine and sewing machine

Info

Publication number: CN106894175B
Application number: CN201710215982.XA
Authority: CN
Inventors: 郑吉�; 祝书伟; 柯祥林; 位延辉
Original assignee: Jack Sewing Machine Co Ltd
Current assignee: Jack Technology Co Ltd
Priority date: 2017-04-01
Filing date: 2017-04-01
Publication date: 2020-01-31
Anticipated expiration: 2037-04-01
Also published as: CN106894175A

Abstract

The invention provides an automatic trimming mechanism of a sewing machine, which comprises a lower shaft, a trimming driving cam fixed on the lower shaft, a movable knife assembly which can swing around the lower shaft and is provided with at least movable knives and movable knife rests, a crank shaft, a trimming driving assembly arranged at the end of the crank shaft, a trimming crank fixed at the other end of the crank shaft and a trimming connecting rod, wherein the trimming driving assembly is provided with a -th extension arm, the end part of the -th extension arm is connected with a roller, two ends of the trimming connecting rod are respectively hinged with the trimming crank and the movable knife rests, the distance L1 between the crank shaft and the hinging point of the trimming crank and the trimming connecting rod is not less than 2.5, the ratio of the distance L2 between the lower shaft and the hinging point of the movable knife rests and the hinging point of the trimming connecting rod and the movable knife rests is not less than 40 degrees, and the roller is matched with the trimming contact surface at the periphery of the trimming driving cam during trimming.

Description

automatic thread trimming mechanism of sewing machine and sewing machine

Technical Field

The invention relates to kinds of sewing equipment, in particular to an automatic thread trimming mechanism of kinds of sewing machines and the sewing machines.

Background

At present, an automatic thread cutting mechanism is configured on a sewing machine (particularly a flat sewing machine) and used for cutting a bottom thread and an upper thread at a rotating shuttle after each sewing is finished, as shown in fig. 1, an automatic thread cutting mechanism in the existing sewing machine generally comprises a rotatable lower shaft 100, a cam 200 fixed on the lower shaft 100, a thread cutting spool 300 parallel to the lower shaft 100, a swingable thread cutting crank assembly 400, a disc 500 positioned at the end of a thread cutting spool 300 , a thread cutting crank 600 fixed at the other end of the thread cutting spool 300, a thread cutting connecting rod 700, a movable knife rest 800, a movable knife 900 fixed on the movable knife rest 800, and a fixed knife 110 fixed on the lower end face of a sewing plate, wherein the thread cutting crank assembly 400 is provided with a -th extension arm 401, a second extension arm 402 and a third extension arm 403, the -th extension arm 401 is used for being matched with the cam to realize power transmission, the second extension arm 402 is used for being matched with the cam to realize forced reset, a slider is installed on the third extension arm 403, a spool 500 is used for realizing the circumferential torque transmission, the transmission of the thread cutting crank assembly, the automatic thread cutting mechanism is matched with the cam 300, the swinging crank assembly, the cam 300, the swinging crank assembly 400 is used for driving the thread cutting spool 200, the thread cutting crank assembly, the swinging crank assembly 400 is used for driving the thread cutting spool 200, the swinging crank assembly 400 is matched with the cam 300, the swinging crank assembly.

In addition, when the sewing machine normally works, the th extension arm 401 on the thread cutting crank assembly 400 needs to be far away from the cam 200, so the thread cutting crank assembly 400 can reciprocate along the axial direction of the thread cutting shaft 300, and a sliding pair needs to be arranged between the third extension arm 403 and the disc 500 of the thread cutting shaft 300.

Further , in the existing automatic thread trimming mechanism shown in fig. 1 and 2, in the thread trimming executing mechanism ABCD composed of the thread trimming crank, the thread trimming connecting rod and the movable knife holder, the ratio of the length of the rod between the rod AB (i.e. a part of the thread trimming crank) and the rod CD (i.e. a part of the movable knife holder) is AB/CD approximately equal to 1.2, and the ratio of the swing angle of the rod EF (i.e. a third extension arm), the rod AB and the rod CD in the thread trimming process is Φ AB: Φ CD 1: 2.58: 3.33, and it is obvious that after the swing angle of the rod EF is amplified by the thread trimming crank assembly and the thread trimming executing mechanism ABCD in two stages, the large-angle rotary motion of the movable knife is finally realized, thereby causing the redundancy of the transmission chain of the automatic thread trimming mechanism and the complex structure.

Disclosure of Invention

In view of the above-mentioned shortcomings of the prior art, it is an object of the present invention to provide an automatic thread trimming mechanism for sewing machines, which simplifies the drive chain, reduces the cost, and reduces the assembly time.

In order to achieve the purpose, the invention provides automatic thread trimming mechanism of a sewing machine, which comprises a lower shaft, a thread trimming driving cam and a movable cutter assembly, wherein the lower shaft is rotatably supported in a bottom plate of the sewing machine, the thread trimming driving cam is fixed on the lower shaft, the movable cutter assembly can swing around the lower shaft, the movable cutter assembly comprises at least movable cutters and a movable cutter holder used for mounting the movable cutters, the movable cutter assembly further comprises a crank shaft parallel to the lower shaft, a thread trimming driving assembly mounted at the end of the crank shaft , a thread trimming crank fixed at the other end of the crank shaft and a thread trimming connecting rod, the thread trimming driving assembly is provided with a -th extension arm, the end part of the -th extension arm is connected with a roller, the two ends of the thread trimming connecting rod are respectively hinged with the thread trimming crank and the movable cutter holder, the distance L1 between the crank shaft and the hinged point of the thread trimming connecting rod and the distance L2 between the lower shaft and the hinged point of the movable cutter holder and the thread trimming connecting rod are not less than 2.5, and when the thread trimming is performed, the contact surface at the periphery of the crank shaft and the thread trimming driving assembly.

, the cutting line driving assembly is provided with a second extension arm, the th extension arm and the second extension arm are respectively positioned at two ends of the cutting line driving assembly, the end part of the second extension arm is connected with a forced reset pin, a forced reset driving cam is fixed on the lower shaft, and when the roller passes over the tail end of a cutting line section on the cutting line contact surface, the forced reset pin is close to the forced reset contact surface on the periphery of the forced reset driving cam.

, it also includes a power source connected with the thread cutting driving component through the transmission mechanism, when cutting thread, the power source acts to drive the thread cutting driving component to move along the axial direction of the crank shaft through the transmission mechanism, to make the roller match with the thread cutting contact surface, and make the forced reset pin locate at the periphery of the forced reset contact surface.

Preferably, the power source is an electromagnet and is provided with a mandrel parallel to the lower shaft, the transmission mechanism comprises a mandrel and a connecting block, the end part of the mandrel is fixed in the connecting block, the end of the mandrel is fixed in the connecting block, and the other end of the mandrel is abutted to the end surface of the trimming driving component.

, the trimming driving assembly has a driving body part located between the th extension arm and the second extension arm, the driving body part is provided with a sliding slot extending along the axial direction of the crank shaft, the crank shaft is arranged in the driving body part in a penetrating way, and the crank shaft is fixed with a limit pin which is located in the sliding slot of the driving body part and can slide back and forth along the extending direction of the sliding slot.

Preferably, the crank shaft is sleeved with a return spring and is fixedly provided with a retaining ring, the retaining ring is positioned between the trimming crank and the second extension arm, and two ends of the return spring are respectively abutted to the second extension arm and the retaining ring.

Preferably, the crank shaft is sleeved with a reset torsion spring, and two ends of the reset torsion spring are respectively abutted to the thread cutting crank and the sewing machine bottom plate.

, the thread cutting crank comprises a crank part and a connecting rod part which are independent from each other, wherein the end of the crank part is fixed with the crank shaft, the other end of the crank part is fixed with the end of the connecting rod part, and the other end of the connecting rod part is hinged with the thread cutting connecting rod.

Preferably, the lower end face of the bottom plate of the sewing machine is provided with a limiting face, the end face of the crank portion facing the limiting face is provided with an accommodating hole, a limiting pad is arranged in the accommodating hole, and the limiting pad is matched with the limiting face.

steps, it also includes a fixed knife fixed on the bottom plate of the sewing machine, moving knives, moving knife stands, the moving knives and the fixed knife are engaged when cutting thread.

The application also provides kinds of sewing machines, including the sewing machine bottom plate and as above the automatic thread trimmer devices of sewing machine, lower shaft and movable cutter frame all rotationally install in the sewing machine bottom plate.

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

this application simplifies structure and the driving chain of automatic thread trimmer of sewing machine mechanism, reduces the quantity of complicated part in original mechanism, is favorable to reduce cost, improves assembly efficiency and reduces assembly man-hour.

Drawings

Fig. 1 is a schematic structural view of an automatic thread trimming mechanism of a sewing machine in the prior art.

Fig. 2 is a schematic diagram of fig. 1.

Fig. 3 is a schematic structural view of an automatic thread trimming mechanism of the sewing machine according to the present application.

Fig. 4 and 5 are schematic structural views of the sewing machine shown in fig. 3 with a sewing machine bottom plate omitted.

FIG. 6 is a schematic view of the connection between the trimming crank and the bed of the sewing machine of FIG. 3.

Fig. 7 is a schematic structural diagram of the trimming driving assembly in fig. 3.

Fig. 8 is a schematic structural view of the cam in fig. 3.

Fig. 9 and 10 are schematic diagrams of an automatic thread trimming mechanism of a sewing machine according to the present application, in which fig. 9 is a thread trimming state and fig. 10 is a reset state.

Description of the element reference numerals

1 Sewing machine bottom plate

101 limiting surface

2 lower shaft

3 drive cam

31 trimming driving cam

32 shear line contact surface

33 forced reset driving cam

34 forced reset contact surface

35 connecting piece

4 move the tool post

5 move sword

6 fixed knife

7 crankshaft

8 wire cutting driving assembly

81 st extending arm

82 roller

83 second extension arm

84 forced reset pin

85 drive body part

86 chute

87 spacing pin

88 roller shaft

9 thread cutting crank

91 crank part

92 link part

10 shear line connecting rod

11 power source

12 ejector pin

13 connecting block

14 return spring

15 retainer ring

16 reset torsion spring

17 limiting pad

18 fixed mount

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 in the specification are for illustrative purposes only and are not intended to limit the scope of the present invention, which is to be construed as being within the scope of the present invention.

The application provides automatic thread cutting mechanism of a sewing machine, which is installed in the sewing machine, particularly a flat sewing machine and is used for cutting a bottom thread and an upper thread after each sewing is finished, for convenience of description, the moving direction of cloth during sewing of the sewing machine is defined as the front direction, the extending direction of a lower shaft 2 in the sewing machine is the left-right direction, the end, close to a machine head, of the lower shaft 2 is the left end, the end, close to a machine tail, of the lower shaft 2 is the right end, for convenience of description, the automatic thread cutting mechanism of the sewing machine comprises a lower shaft 2 rotatably supported in a bottom plate 1 of the sewing machine, a thread cutting driving cam 31 fixed on the lower shaft 2, a movable knife component 865 installed in a bottom plate 1 of the sewing machine and capable of swinging around the lower shaft 2, a crank shaft 7 parallel to the lower shaft 2, a thread cutting driving component 8 installed at the right end of the crank shaft 7, a thread cutting crank shaft 9 fixed at the left end of the crank shaft 7, a thread cutting crank shaft 10 connecting rod 10, the movable knife component 8 is installed at least in a handle 23, the crank shaft 2 and a movable knife rack 4, the movable knife component 2 is installed at a distance from a crank shaft 2L 2.

, the sewing machine can be of a single-blade structure or a double-blade structure, when the sewing machine adopts the structure of a single blade, the automatic thread cutting mechanism of the sewing machine further comprises fixed blades 6 fixed on the lower end face of the sewing machine bottom plate 1, movable blades 5 and movable blade holders 4, when the sewing machine adopts the structure of the double-blade, the movable blades 5 are two, the two movable blade holders 4 are two, the two movable blades 5 are respectively fixed on movable blade holders 4, for example, the two short-thread-head double-thread cutting mechanisms disclosed in the Chinese patent application specification with the application number of 201610473636.7 or the thread cutting mechanisms of the sewing machine disclosed in the Chinese patent application specification with the application number of 201610494020.8, at the moment, the two movable blade holders 4 can be respectively driven by the thread cutting cranks 9 fixed on the crank shaft 7 to swing, so that the two thread cutting cranks 9 are provided, when the two movable blades 5 are meshed, the following embodiments of the automatic thread cutting mechanism are provided by the single-blade cutting mechanism.

Fig. 9 and 10 show a schematic diagram of an automatic thread trimming mechanism of a sewing machine with a single-blade structure, wherein a corresponds to a crank shaft 7, G corresponds to a roller 82, D corresponds to a lower shaft 2, AG corresponds to a -th extension arm 81, AB corresponds to a thread trimming crank 9, BC corresponds to a thread trimming link 10, CDE corresponds to a movable knife rest 4, and the thread trimming crank 9, the thread trimming link 10 and the movable knife rest 4 form a four-bar mechanism ABCD for thread trimming, so that B is a hinge point of the thread trimming crank 9 and the thread trimming link 10, C is a hinge point of the thread trimming link 10 and the movable knife rest 4, so that a distance L1 between the hinge points of the four-bar crank shaft 7, the thread trimming crank 9 and the thread trimming link 10 is a length of a bar AB in fig. 9 or 10, a distance L2 between the lower shaft 2, the movable knife rest 4 and the thread trimming link 10 is a length of the bar CD in fig. 9 or 10, the distance CD 2 between the lower shaft 2, the hinge point of the thread trimming link 4 and the hinge point of the thread trimming link 10 is a length of the bar CD 5, and the cam angle BC 35 of the automatic thread trimming link can be optimized by a large angle of the automatic thread trimming link CD mechanism BC 40.

In the embodiment, the trimming contact surface 32 on the periphery of the trimming drive cam 31 comprises a to-be-trimmed line segment, a trimming line segment and a reset segment which are sequentially connected at first positions, the trimming drive assembly 8 is at an initial position during normal sewing, at the moment, the roller 82 is not arranged on the periphery of the trimming drive cam 31 and has no matching relation with the trimming contact surface 32, after sewing is finished, the trimming drive assembly 8 moves towards the direction close to the trimming drive cam 31 to drive the extension arm 81 and the roller 82 to synchronously move towards the direction close to the trimming drive cam 31, so that the roller 82 is positioned on the periphery of the trimming drive cam 31 and is in contact with the to-be-trimmed line segment of the trimming contact surface 32, at the moment, as shown in fig. 4, 5 and 9, the lower shaft 2 drives the trimming drive cam 31 to synchronously rotate, namely, the trimming drive assembly 8, the crank shaft 7 and the trimming line 9 are driven to synchronously swing through the matching relation of the trimming contact surface 32 on the trimming drive cam 31 and the roller 82, the trimming drive assembly of the trimming drive assembly cam 8, the crank shaft 10 and the cutting drive mechanism, the cutting mechanism is capable of automatically reducing the sewing speed of cutting thread, reducing the sewing machine, the sewing machine cost of cutting thread, reducing the sewing machine, and the sewing machine cutting cost of the sewing machine, and reducing the sewing machine, and reducing the sewing machine cost of the sewing machine.

The roller 82 may be in a stationary state or a rolling state, and in this embodiment, it is preferable that the roller 82 is in a rolling state, so as to reduce the friction between the roller 82 and the trimming contact surface 32 when the roller 82 is engaged with the trimming contact surface 32, at this time, as shown in fig. 7, a roller shaft 88 extending from the left to the right of is fixed to the end of the extending arm 81 of the trimming driving assembly 8, and the roller 82 is rotatably sleeved on the roller shaft 88 and located at the left side of the extending arm 81.

Preferably, as shown in fig. 4 and 5, a return torsion spring 16 is sleeved on the crank shaft 7, and two ends of the return torsion spring 16 are respectively abutted against the trimming crank 9 and the sewing machine bottom plate 1; when the sewing thread is cut off, the roller 82 is matched with the reset section on the sewing thread contact surface 32, the sewing thread crank 9 resets under the action of the reset torsion spring 16, and the movable knife rest 4, the movable knife 5, the crank shaft 7 and the sewing thread drive assembly 8 are driven to reset through the sewing thread connecting rod 10.

, as shown in fig. 4 and 5, 7, 9 and 10, the left end of the trimming drive assembly 8 has a second extension arm 83, the end of the second extension arm 83 away from the crank shaft 7 is connected with a forcible reset pin 84, the forcible reset pin 84 protrudes rightwards from the right end face of the second extension arm 83, the lower shaft 2 is fixed with a forcible reset drive cam 33, the outer peripheral surface of the forcible reset drive cam 33 is a forcible reset contact surface 34, when the trimming drive assembly 8 moves towards the trimming drive cam 31, the trimming drive assembly 8 drives the second extension arm 83 and the forcible reset pin 84 to move towards the direction of the forcible reset drive cam 33 synchronously, so that the forcible reset pin 84 is located at the outer peripheral side of the forcible reset contact surface 34, when the movable knife 5 and the fixed knife 6 are engaged to cut a trimming line, the forcible reset pin 84 crosses the connecting point of the trimming segment and reset section on the trimming contact surface 32, the forcible reset crank shaft 84, the forcible reset pin 84 is inserted into the crank shaft 14, the crank shaft 84 is moved towards the crank shaft 34, the crank shaft 7 is moved towards the crank shaft 7, the crank shaft 7, the crank shaft, the.

Preferably, as shown in fig. 8, the trimming driving cam 31 and the forced resetting driving cam 33 are connected by a connecting piece 35, the trimming driving cam 31 and the forced resetting driving cam 33 are respectively positioned at the right side and the left side of the connecting piece 35, the trimming driving cam 31, the connecting piece 35 and the forced resetting driving cam 33 are processed into integral pieces, and the integral pieces are defined as the driving cams 3, in the driving cams 3, the connecting piece 35 is fixed on the lower shaft 2 by a plurality of screws arranged along the radial direction of the lower shaft 2, so that the driving cams 3 are integrally fixed with the lower shaft 2, which is beneficial to saving space and facilitating assembly.

In this embodiment, the wire cutting drive assembly 8 is linearly and reciprocally movable along the axial direction of the crank shaft 7 to engage or disengage the roller 82 with or from the wire cutting contact surface 32 and to bring the forcible return pin 84 close to or away from the forcible return contact surface 34. At this time, as shown in fig. 4 and 5, the automatic thread trimming mechanism of the sewing machine further comprises a power source 11, and the power source 11 is connected with the thread trimming driving assembly 8 through a transmission mechanism; during thread cutting, the power source 11 is operated to drive the thread cutting driving assembly 8 to move leftwards along the axial direction of the crank shaft 7 through the transmission mechanism, so that the roller 82 is matched with the thread cutting contact surface 32, and the forced resetting pin 84 is positioned on the outer peripheral side of the forced resetting contact surface 34. The crank shaft 7 is further sleeved with a return spring 14 and is fixedly provided with a retaining ring 15, the retaining ring 15 is positioned between the trimming crank 9 and the second extension arm 83, and two ends of the return spring 14 are respectively abutted against the second extension arm 83 and the retaining ring 15; after the thread cutting is finished, the power source 11 is reset, the second extension arm 83 is moved rightwards through the elastic force of the reset spring 14, and then the thread cutting driving assembly 8 is driven to move rightwards and reset.

Preferably, the power source 11 is an electromagnet and has a mandrel parallel to the lower shaft 2, the electromagnet is mounted on the lower end surface of the bottom plate 1 of the sewing machine through the fixing frame 18, the transmission mechanism includes a top rod 12 and a connecting block 13, the left end of the mandrel is fixed in the connecting block 13, the right end of the top rod 12 is fixed in the connecting block 13, the left end of the top rod 12 abuts against the right end surface of the extending arm 81 of the trimming drive assembly 8, during trimming, the electromagnet is energized, the iron core of the electromagnet retracts leftward in the direction close to the electromagnet under the action of magnetic force, so the mandrel of the electromagnet extends leftward, drives the connecting block 13 and the top rod 12 to move leftward synchronously, and further pushes the trimming drive assembly 8 to move leftward, in order to achieve guidance during left-right movement of the trimming drive assembly 8 and transmission of torque between the trimming drive assembly 8 and the crank shaft 7, as shown in fig. 5 and 7, the trimming drive assembly 8 has a drive body 85 located between the extending arm 81 and the second extending arm, the drive body 85 is provided with a sliding groove 86 extending in the axial direction of the crank shaft 7, and the drive pin 85 is slidably located on the peripheral surface of the reciprocating pin, and the crank shaft 85.

In order to further steps to simplify the structure of parts and reduce the cost, as shown in fig. 5 and 6, the trimming crank 9 is divided into two independent parts, namely a part and a crank part 91, and a part two and a connecting rod part 92, wherein the end of the crank part 91 is fixed with the crank shaft 7, the other end of the crank part 91 is fixed with the end of the connecting rod part 92 through two screws to assemble the trimming crank 9, the other end of the connecting rod part 92 is hinged with the trimming connecting rod 10, after the trimming crank 9 is divided, the structure of the crank part 91 and the connecting rod part 92 can be simplified, and the cost of parts is reduced, as shown in fig. 6, a limiting surface 101 is arranged on the lower end surface of the sewing machine base plate 1, a containing hole is arranged on the end surface of the crank part 91 of the trimming crank 9 facing the limiting surface 101, a limiting pad 17 made of rubber is arranged in the containing hole, and the limiting pad 17 is matched with the limiting surface 101, so as to limit the initial positions of the movable knife rest 4 and the movable knife.

The automatic thread cutting mechanism of the sewing machine has the working principle that in an initial state, the electromagnet is powered off, an iron core of the electromagnet is in a state of extending rightward, the thread cutting driving component 8 is located on the right side of the driving cam 3, the roller 82 is separated from the thread cutting contact surface 32, the movable cutter 5 is separated from the fixed cutter 6, when thread cutting is carried out, the electromagnet is powered on, the mandrel moves leftward, the thread cutting driving component 8 is pushed by the fixing block and the ejector rod 12 to move leftward against the pressure of the reset spring 14, the reset spring 14 is compressed, the roller 82 is located on the outer peripheral side of the thread cutting driving cam 31 and is in contact with a thread section to be cut of the thread cutting contact surface 32, the lower shaft 2 drives the driving cam 3 to rotate synchronously, the roller 82 is matched with the thread cutting section of the thread cutting contact surface 32 to drive the thread cutting driving component 8 to swing, the thread cutting driving component 8 drives the crank shaft 7 and the thread cutting crank shaft 9 to swing synchronously through the limit pin 87, the thread cutting crank shaft 9 transmits power to the movable cutter frame 4 through the thread cutting connecting rod 10, finally, the movable cutter frame 4 and the movable cutter 5 swing in the direction close to the fixed cutter 6 until the bottom thread cutting surface and the crank shaft 2 and the thread cutting surface are driven by the reset spring, the thread cutting driving component, the thread cutting pad 14, the thread cutting driving crank shaft 32 is driven by the reset spring, and the thread cutting mechanism 14, and the thread cutting mechanism, and the crank shaft, and the thread cutting mechanism 14, and the thread.

The application also provides kinds of sewing machines, including sewing machine bottom plate 1 and as above the automatic thread trimmer devices of sewing machine, lower shaft 2 and moving knife rest 4 all rotationally install in sewing machine bottom plate 1.

In summary, the automatic thread trimming mechanism of the sewing machine is optimized, and particularly, parameters of a screw rod mechanism ABCD for executing thread trimming in the automatic thread trimming mechanism of the sewing machine are optimally designed, so that a transmission chain is simplified, assembly is facilitated, and assembly time is reduced; meanwhile, the structure of a thread cutting shaft, a sliding block, a sliding pair and the like in the original mechanism is cancelled, and the pin shaft type matching with lower cost is adopted, so that the number of complex parts in the automatic thread cutting mechanism of the sewing machine is reduced, and the production cost is greatly reduced. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.

It will be appreciated by those skilled in the art that modifications and variations can be made to the disclosed embodiments without departing from the spirit and scope of the invention, and therefore, is equivalent to modifications and variations that would be apparent to those skilled in the art without departing from the spirit and scope of the invention as disclosed in the appended claims.

Claims

The automatic thread trimming mechanism of the sewing machine is characterized by further comprising a crank shaft (7) parallel to the lower shaft (2), a thread trimming driving assembly (8) installed at the end of the crank shaft (7), a thread trimming crank (9) fixed at the other end of the crank shaft (7) and a thread trimming connecting rod (10), the thread trimming driving assembly (8) is provided with a -th extension arm (81), the end of the -th extension arm (81) is connected with a roller (82), two ends of the thread trimming connecting rod (10) are respectively hinged with the thread trimming crank (9) and the thread trimming frame (4), two ends of the crank shaft (7), the thread trimming crank (9) and the thread trimming connecting rod (4) are respectively hinged with the thread trimming connecting rod (4), the distances between the hinge point of the crank shaft (7), the thread trimming crank shaft (9) and the thread trimming connecting rod (10) and the thread trimming driving assembly (10) are smaller than the distances between the lower shaft (1) rotatably supported in a sewing machine base (1), the thread trimming driving cam (31) and the thread trimming assembly (2), and the movable knife assembly (4) which can swing around the lower shaft (2), the movable knife assembly (3), the movable knife assembly (5) and the movable knife rest (4) for mounting the movable knife (5), the movable knife (10), the movable knife rest (10), the movable knife (10) is used for driving assembly (10) when the thread trimming mechanism (10) is not reset wire (10) and the movable knife (10), the thread trimming mechanism (10), the movable knife (4), the movable knife (10) is not reset spring (10), the movable knife (10) is in contact with the normal reset spring (10), the movable knife (10), the normal reset spring (10), the movable.
2. The automatic thread trimming mechanism of sewing machine according to claim 1, characterized in that the thread trimming driving assembly (8) has a second extension arm (83), the th extension arm (81) and the second extension arm (83) are respectively located at two ends of the thread trimming driving assembly (8), the end of the second extension arm (83) is connected with a forced resetting pin (84), the lower shaft (2) is fixed with a forced resetting driving cam (33), and when the roller (82) crosses the tail end of the thread trimming segment on the thread trimming contact surface (32), the forced resetting pin (84) is close to the forced resetting contact surface (34) at the periphery of the forced resetting driving cam (33).
3. The automatic thread trimming mechanism of a sewing machine according to claim 2, characterized in that: the wire cutting machine also comprises a power source (11), wherein the power source (11) is connected with the wire cutting driving assembly (8) through a transmission mechanism; when in thread cutting, the power source (11) acts, the thread cutting driving assembly (8) is driven by the transmission mechanism to move along the axial direction of the crank shaft (7), the roller (82) is matched with the thread cutting contact surface (32), and the forced resetting pin (84) is positioned on the outer peripheral side of the forced resetting contact surface (34).
4. The automatic thread trimming mechanism of sewing machine according to claim 3, characterized in that the power source (11) is an electromagnet and has a mandrel parallel to the lower shaft (2), the transmission mechanism comprises a top rod (12) and a connecting block (13), the end of the mandrel is fixed in the connecting block (13), the end of the top rod (12) is fixed in the connecting block (13), and the other end of the top rod (12) abuts against the end face of the thread trimming driving component (8).
5. The automatic thread trimming mechanism of sewing machine according to claim 2, wherein the thread trimming driving assembly (8) has a driving body portion (85) located between the th extension arm (81) and the second extension arm (83), the driving body portion (85) is provided with a sliding slot (86) extending along the axial direction of the crank shaft (7), the crank shaft (7) is arranged in the driving body portion (85) in a penetrating manner, the crank shaft (7) is fixed with a limit pin (87), and the limit pin (87) is located in the sliding slot (86) of the driving body portion (85) and can slide in a reciprocating manner along the extending direction of the sliding slot (86).
6. The automatic thread trimming mechanism of a sewing machine according to claim 2, characterized in that: the improved trimming machine is characterized in that a return spring (14) is sleeved on the crank shaft (7) and fixedly located on a check ring (15), the check ring (15) is located between the trimming crank (9) and the second extension arm (83), and two ends of the return spring (14) are respectively abutted to the second extension arm (83) and the check ring (15).
7. The automatic thread trimming mechanism of sewing machine according to claim 1, wherein the thread trimming crank (9) comprises a crank portion (91) and a link portion (92) which are independent of each other, the end of the crank portion (91) is fixed to the crank shaft (7), the other end of the crank portion (91) is fixed to the end of the link portion (92), and the other end of the link portion (92) is hinged to the thread trimming link (10).
8. The automatic thread trimming mechanism of a sewing machine according to claim 7, wherein: be equipped with spacing face (101) on the lower terminal surface of sewing machine bottom plate (1), the accepting hole has been seted up towards on the terminal surface of spacing face (101) to bent portion (91), and it has spacing pad (17) to embed in this accepting hole, spacing pad (17) cooperate with spacing face (101).
9. The automatic thread trimming mechanism of the sewing machine according to claim 1, further comprising a fixed knife (6) fixed on the bottom plate (1) of the sewing machine, wherein movable knives (5) are provided, movable knife rests (4) are provided, and the movable knives (5) are engaged with the fixed knife (6) during thread trimming.
10, Sewing machine, comprising a sewing machine bottom plate (1), characterized in that, it also comprises the automatic thread trimming mechanism of sewing machine according to any claims 1-9, the said lower shaft (2) and moving blade holder (4) are all rotatably mounted in the sewing machine bottom plate (1).