A sewing machine thread trimming mechanism, seam starter and bird nest prevention thread trimming method, and sewing machine

Abstract

The present invention provides a sewing machine thread trimming mechanism, a method for trimming threads at seam start and preventing bird nests, and a sewing machine. The sewing machine thread trimming mechanism includes a first thread trimmer, a movable thread trimmer, a needle drop drive cam, a thread trimmer cam at seam start, a thread trimmer cam crank rotatably and movably supported on a sewing machine base, a first roller mounted on the thread trimmer cam crank, a second roller movably mounted on the thread trimmer cam crank, a thread trimmer transmission assembly, a first clutch drive source, and a second clutch drive source. The movable thread trimmer is provided with a needle drop hole at seam start. The needle drop drive cam and the thread trimmer cam at seam start are both fixed to a rotatable shaft component in the sewing machine. The first clutch drive source is fixed to the sewing machine base and acts on the thread trimmer cam crank. The second clutch drive source is fixed to the thread trimmer cam crank and acts on the second roller. The thread trimmer cam crank is transmission-connected to the movable thread trimmer via the thread trimmer transmission assembly. The present invention achieves seam start and bird nest prevention at low cost and reliably, resulting in beautiful seam stitches on the front of the sewing material.

Description

Technical Field

[0001] The present invention relates to the technical field of sewing machines, in particular to a sewing machine thread trimming mechanism, a seam start-up and bird nest prevention thread trimming method using the sewing machine thread trimming mechanism, and a sewing machine equipped with the sewing machine thread trimming mechanism. Background Art

[0002] When starting a seam on a sewing machine, a certain length of thread is typically left on one side of the needle to prevent the upper thread from escaping the needle eye during the process. However, if this length of thread remains on the front of the sewing material, it must be manually trimmed after sewing, significantly reducing efficiency. If the thread is carried to the back of the sewing material, it can easily form a large bird's nest on the back of the sewing material. To address this, sewing machines are equipped with an anti-bird's nest thread trimming mechanism to trim the thread at the start of the seam to prevent the formation of bird's nests.

[0003] Chinese invention patent application number 201510349411.6 discloses a sewing machine bird's nest removal device. The device comprises a hook, a thread clamp, a needle, and a presser foot located below the machine head. The hook is connected to the machine head via a rotating shaft, and the presser foot has a thread slot corresponding to the needle, with a thread cutter at the bottom. The hook clamps the thread end on the needle side after thread trimming. The movement of the fabric transfers the clamped thread end to the presser foot, where it is cut near the needle hole in the sewing material, leaving a short remaining thread end and thus solving the problem of bird's nests. However, this sewing machine bird's nest removal device still has some problems: 1. A small amount of thread end remains on the front of the sewing material, affecting the appearance; 2. The presser foot is a custom-made component that cannot be applied to other sewing processes, resulting in high cost and poor versatility; 3. The hook's thread-holding stability is relatively low during actual operation, resulting in poor reliability of the bird's nest prevention device.

[0004] To address the aforementioned issues with existing bird's nest removal devices in sewing machines, some machines are equipped with a movable knife thread trimming mechanism. This mechanism includes a movable knife that rotates beneath the needle plate, an independent thread trimming motor, and a thread trimming transmission assembly. The thread trimming motor is connected to the movable knife via the thread trimming transmission assembly. For example, a thread trimming mechanism is disclosed in Chinese invention patent application number 201811350563.8. However, this thread trimming mechanism uses an independent motor, which increases the cost of the sewing machine. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a sewing machine thread trimming mechanism that does not require an additional motor to drive the thread trimming movable knife to move, thereby achieving low-cost and reliable seam starter anti-bird nesting.

[0006] To achieve the above-mentioned object, the present invention provides a thread trimming mechanism of a sewing machine, comprising a first thread trimmer, a movable thread trimmer knife provided on the outer peripheral side of a lower shaft of the sewing machine and capable of movement, a needle drop driving cam, a seam start and thread trimmer cam, a thread trimmer cam crank rotatably and movably supported on a bottom plate of the sewing machine, a first roller mounted on the thread trimmer cam crank, a second roller movably mounted on the thread trimmer cam crank, a thread trimmer transmission assembly, a first clutch driving source, and a second clutch driving source, wherein the first thread trimmer is provided with a first blade, the movable thread trimmer knife is provided with a through seam start and needle drop hole and a front thread trimmer blade, the needle drop driving cam and the seam start and thread trimmer cam are both fixed on a rotatable shaft component in the sewing machine, the first clutch driving source is fixed to the bottom plate of the sewing machine and acts on the thread trimmer cam crank, the second clutch driving source is fixed to the thread trimmer cam crank and acts on the second roller, and the thread trimmer cam crank is transmission-connected to the movable thread trimmer knife through the thread trimmer transmission assembly;

[0007] When the first clutch driving source is not in operation, no power is transmitted between the first roller and the needle drop driving cam and the seam start and thread trimming cam; when the first clutch driving source is in operation, the first roller can contact and cooperate with the needle drop driving cam;

[0008] When the second clutch drive source is not in operation, there is no power transmission between the second roller and the needle drop drive cam and the seam start and thread trimmer cam; when the second clutch drive source is in operation, the second roller can contact and cooperate with the seam start and thread trimmer cam.

[0009] Furthermore, the shaft component is a lower shaft, a tooth-lifting shaft or a feeding shaft of a sewing machine.

[0010] Furthermore, the first clutch drive source is an electromagnet, the thread trimming cam crank has a crank shaft, a crank body fixed to the crank shaft, and a first crank arm and a second crank arm extending integrally from the crank body, the crank shaft is rotatably and movably supported in the sewing machine base, the electromagnet core of the first clutch drive source is axially opposite to the crank shaft, the first roller is mounted on the first crank arm, the second roller is movably mounted on the second crank arm, the second clutch drive source is an electromagnet fixed to the second crank arm, and the electromagnet core of the second clutch drive source is axially opposite to the second roller.

[0011] Furthermore, the thread trimming cam crank is fixed with a third crank arm, and the thread trimming transmission assembly includes a thread trimming slider rotatably mounted on the third crank arm, a thread trimming shaft rotatably supported in the sewing machine base, a thread trimming crank fixed at one end of the thread trimming shaft, a thread trimming connecting rod, and a first knife holder rotatably assembled on the outer periphery of the lower shaft, the other end of the thread trimming shaft is integrally provided with a shaft arm portion, and the shaft arm portion is provided with a first thread trimming groove that slides and contacts with the thread trimming slider, the two ends of the thread trimming connecting rod are respectively hinged to the thread trimming crank and the first knife holder, and the thread trimming movable knife is fixed to the first knife holder.

[0012] Furthermore, the thread trimmer transmission assembly also includes a first reset torsion spring and a second reset torsion spring. The first reset torsion spring is sleeved on the thread trimmer shaft and acts on the thread trimmer crank. A support sleeve is provided on the sewing machine bottom plate. The second reset torsion spring is sleeved on the support sleeve and acts on the thread trimmer cam crank.

[0013] Furthermore, the first thread cutting knife is a fixed knife;

[0014] When the first clutch driving source and the second clutch driving source are both inactive, the first thread trimmer and the movable thread trimmer are located on the same side of the needle of the sewing machine.

[0015] Furthermore, the thread trimming mechanism of the sewing machine further includes a rear thread trimming cam, a second thread trimming knife movable on the outer peripheral side of the lower shaft of the sewing machine, and a stroke control electromagnet, wherein the rear thread trimming cam is fixed to a rotatable shaft component in the sewing machine, the thread trimming movable knife is provided with a rear thread trimming blade, the second thread trimming knife is provided with a second blade, the second thread trimming knife is transmission-connected to the thread trimming transmission assembly, and the stroke control electromagnet acts on the first clutch drive source;

[0016] When the stroke control electromagnet is powered off and the first clutch drive source is inactive, no power is transmitted between the first roller and the rear thread trimming cam, and the second thread trimming knife and the movable thread trimming knife are distributed on both sides of the needle in the sewing machine;

[0017] When the stroke control electromagnet is energized and the first clutch drive source is activated, the first roller can contact and cooperate with the rear thread trimming cam, and the thread trimming movable knife and the second thread trimming knife are driven to move toward each other through the thread trimming cam crank and the thread trimming transmission assembly, so that the rear thread trimming blade is engaged with the second blade.

[0018] Furthermore, the thread trimming cam crank is fixed with a third crank arm, and the thread trimming transmission assembly includes a thread trimming slider rotatably mounted on the third crank arm, a thread trimming shaft rotatably supported in the sewing machine base, a thread trimming crank fixed at one end of the thread trimming shaft, a thread trimming connecting rod, a first knife holder rotatably assembled on the outer periphery of the lower shaft, a second knife holder rotatably assembled on the outer periphery of the lower shaft, and a thread trimming transmission pin fixed to the second knife holder, the other end of the thread trimming shaft is integrally provided with a shaft arm portion, and the shaft arm portion is provided with a first thread trimming slot that slides and contacts with the thread trimming slider, the two ends of the thread trimming connecting rod are respectively hinged to the thread trimming crank and the first knife holder, the thread trimming movable knife is fixed to the first knife holder, the thread trimming crank is provided with a second thread trimming slot that slides and contacts with the thread trimming transmission pin, and the second thread trimming knife is fixed to the second knife holder.

[0019] Furthermore, the thread trimming mechanism of the sewing machine further comprises an anti-jamming cam, wherein the anti-jamming cam is fixed on a rotatable shaft component in the sewing machine;

[0020] When the stroke control electromagnet is powered off and both the first clutch drive source and the second clutch drive source are inactive, the second roller is distributed on the outer peripheral side of the anti-jamming cam and can contact and cooperate with the anti-jamming cam.

[0021] Furthermore, the needle drop driving cam, the seam start thread trimming cam, the rear thread trimming cam and the anti-jamming knife cam are integrated into a thread trimming driving cam.

[0022] The present application also provides a seam start-up and bird nest prevention thread trimming method, using the sewing machine thread trimming mechanism as described above, the seam start-up and bird nest prevention thread trimming method comprises the following steps in sequence:

[0023] S1. Before the sewing machine starts sewing the first stitch, or during the process of the needle moving downward when the sewing machine starts sewing the first stitch, the first clutch drive source is activated and the second clutch drive source is inactivated. The first clutch drive source drives the thread trimmer cam crank to move, so that the first roller moves to the outer peripheral side of the needle drop drive cam. The shaft component of the sewing machine drives the needle drop drive cam to rotate, and the thread trimmer knife is driven to move through the first roller, the thread trimmer cam crank and the thread trimmer transmission assembly, so that the seam start and needle drop hole is located directly below the needle.

[0024] S2, the sewing machine's first needle moves down, passes through the sewing start needle hole, and under the action of the rotary hook in the sewing machine, the upper thread end on one side of the needle is brought to the bottom of the thread trimming movable knife;

[0025] S3: The first needle of the sewing machine moves up at the start of sewing, the first clutch drive source is reset, the thread trimming cam crank, the first roller and the movable thread trimming knife are reset, the movable thread trimming knife extracts at least a portion of the upper thread end, and no power is transmitted to the first roller, the needle drop drive cam and the sewing start thread trimming cam;

[0026] S4, setting the number of stitches for sewing machine to start sewing;

[0027] S5, the second clutch drive source is activated and the first clutch drive source is inactivated, the second clutch drive source drives the second roller to move to the outer peripheral side of the seam start and thread trimming cam, the shaft component of the sewing machine drives the seam start and thread trimming cam to rotate, and the thread trimming movable knife is driven to move through the second roller, the thread trimming cam crank and the thread trimming transmission assembly until the front thread trimming blade engages with the first blade, thereby cutting the upper thread end;

[0028] S6. The second clutch drive source is reset, and the thread trimming cam crank, the second roller and the thread trimming movable knife are reset.

[0029] The present application further provides a sewing machine, in which the sewing machine thread trimming mechanism as described above is configured.

[0030] As described above, the sewing machine thread trimming mechanism, seam starter and bird nest prevention thread trimming method, and sewing machine according to the present invention have the following beneficial effects.

[0031] The present application uses a first clutch drive source to transmit power between the first roller and the needle drop drive cam, so that the thread trimming movable knife can extract a portion of the upper thread end to the needle plate bottom plate, and pull the upper thread end to the back of the sewing material; and uses a second clutch drive source to transmit power between the second roller and the seam start thread trimming cam, so that the front thread trimming blade and the first blade engage to cut the upper thread end, thereby effectively suppressing the formation of a bird's nest in the sewing material. In particular, the power for driving the thread trimming movable knife in the present application comes from a rotatable shaft component in the sewing machine, that is, from an existing power source in the sewing machine, and there is no need to set up an additional motor to drive the thread trimming movable knife to move, thereby reducing the cost of the sewing machine. Therefore, the present application can achieve anti-bird's nesting at the start of the seam at a low cost and reliably, and the thread ends are only on the back of the sewing material, ensuring that the stitches on the front of the sewing material are beautiful. It has strong versatility and can be applied to various sewing processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic structural diagram of the sewing machine for this application.

[0033] Figure 2 and Figure 3 This is a schematic diagram of the structure of the thread trimming mechanism of the sewing machine of this application at different viewing angles.

[0034] Figure 4 and Figure 5 This is a schematic diagram of the structure of the thread trimming cam crank, thread trimming transmission assembly, thread trimming movable knife and second thread trimming knife in this application at different perspectives.

[0035] Figure 6 This is a structural diagram of the thread trimming movable knife in this application.

[0036] Figure 7 and Figure 8 Schematic diagram of the structure of the thread trimming drive cam in this application at different viewing angles.

[0037] Figure 9 This is a schematic diagram of the angles when the thread trimming cam crank and the thread trimming drive cam cooperate in this application.

[0038] Figure 10 This is a schematic diagram of the relationship between the movable thread trimming knife, the first thread trimming knife and the second thread trimming knife when the thread trimming mechanism of the sewing machine in this application performs a waiting action.

[0039] Figure 11 This is a schematic diagram of the relationship between the movable thread trimming knife, the first thread trimming knife and the second thread trimming knife when the thread trimming mechanism of the sewing machine in this application performs the needle dropping action.

[0040] Figure 12 This is a schematic diagram of the relationship between the movable thread trimming knife, the first thread trimming knife and the second thread trimming knife when the thread trimming mechanism of the sewing machine in this application performs the front thread trimming action.

[0041] Figure 13 This is a schematic diagram of the relationship between the movable thread trimming knife, the first thread trimming knife and the second thread trimming knife when the thread trimming mechanism of the sewing machine in this application performs the rear thread trimming action.

[0042] Component number description: first thread trimmer 10, first blade 11, thread trimmer movable knife 20, seam start and needle drop hole 21, front thread trimmer blade 22, rear thread trimmer blade 23, thread trimmer drive cam 30, needle drop drive cam 31, seam start and thread trimmer cam 32, rear thread trimmer cam 33, anti-jamming knife cam 34, thread trimmer cam crank 40, crank shaft 41, crank body 42, first crank arm 43, second crank arm 44, third crank arm 45, first roller 51, second roller 52, thread trimmer transmission assembly 60, thread trimmer slider 6 1. Thread trimmer shaft 62, shaft arm 621, first thread trimmer chute 622, thread trimmer crank 63, second thread trimmer chute 631, thread trimmer connecting rod 64, first tool holder 65, first return torsion spring 66, second return torsion spring 67, second tool holder 68, thread trimmer transmission pin 69, spring pin 610, first clutch drive source 71, second clutch drive source 72, stroke control electromagnet 73, second thread trimmer 80, second blade 81, bottom plate 90, lower shaft 110, fixed mounting plate 120, movable mounting plate 130. DETAILED DESCRIPTION

[0043] The following describes the implementation of the present invention through specific embodiments. People skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0044] It should be noted that the structures, proportions, sizes, etc. depicted in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions for the implementation of the present invention. Therefore, they have no substantial technical significance. Any modification of the structure, change in the proportional relationship or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose of the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description and are not used to limit the scope of the implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0045] It should also be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or indirectly connected to the other element through an intervening element.

[0046] In addition, the descriptions of "first", "second", etc. in this application are for descriptive purposes only and should not be understood as indicating or implying their relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments can be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in this field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0047] The present application provides a sewing machine thread trimming mechanism, a method for trimming seams to prevent bird nests using the sewing machine thread trimming mechanism, and a sewing machine equipped with the sewing machine thread trimming mechanism. The sewing machine is a flatbed sewing machine having a rotatable main shaft. For ease of description, in the following embodiments, the axial direction of the main shaft in the sewing machine is defined as the left-right direction, and the direction of the main shaft toward the sewing machine head is defined as the left direction; the horizontal direction perpendicular to the left-right direction is defined as the front-back direction, and the direction of movement of the sewing material when the sewing machine is sewing is defined as the front direction; and the vertical direction perpendicular to the left-right direction is defined as the up-down direction.

[0048] Usually, such as Figure 1As shown, the sewing machine includes a sewing machine case and a sewing machine base 90, both of which are fixedly arranged, a needle plate fixed to the sewing machine base 90, a main shaft rotatably supported in the sewing machine case, a lower shaft 110 rotatably supported in the sewing machine base 90, a main motor for driving the main shaft to rotate, a needle bar mechanism with a needle, a rotary hook, a tooth rack, a feed tooth fixed on the tooth rack, a tooth lifting mechanism, and a feeding mechanism. The main shaft and lower shaft 110 in the sewing machine both extend left and right, and are connected to each other via a pulley transmission assembly. The main motor is fixed to the right end surface of the sewing machine housing and connected to the right end of the main shaft. The left end of the main shaft is connected to the needle bar mechanism, driving the needle to move up and down. The rotary shuttle is fixed to the left end of the lower shaft 110 and is directly driven by the lower shaft 110 to rotate. The tooth lifting mechanism is connected to the rear end of the tooth frame and drives the tooth frame and feed dog to move up and down. The tooth lifting mechanism has a tooth lifting shaft that is rotatably supported in the sewing machine base 90 and extends left and right. The tooth lifting shaft extends left and right. The feed mechanism is connected to the front end of the tooth frame and drives the tooth frame and feed dog to move back and forth. The feed mechanism has a feed shaft that is rotatably supported in the sewing machine base 90 and extends left and right. Therefore, the sewing machine has at least the following rotatable shaft components: the main shaft, the lower shaft 110, the tooth lifting shaft, and the feed shaft. In addition, the power source of the tooth lifting mechanism and the power source of the feeding mechanism can both come from the main motor, and then the tooth lifting shaft and the feeding shaft are both connected to the main shaft transmission; of course, the power source of the tooth lifting mechanism and the power source of the feeding mechanism can also be driven by an additional independent motor.

[0049] like Figures 1 to 3 As shown, the thread trimming mechanism of the sewing machine involved in the present application includes a first thread trimmer 10, a thread trimmer movable knife 20, a needle drop drive cam 31, a seam start thread trimmer cam 32, a thread trimmer cam crank 40, a first roller 51, a second roller 52, a thread trimmer transmission assembly 60, a first clutch drive source 71 and a second clutch drive source 72. Among them, the first thread trimmer 10 is arranged on the outer peripheral side of the lower shaft 110, and the first thread trimmer 10 is provided with a first blade 11. The thread trimmer movable knife 20 can be movably arranged on the outer peripheral side of the lower shaft 110 in the sewing machine, as shown in FIG. Figure 6As shown, the thread trimming movable knife 20 is provided with a stitch start and drop needle hole 21 that passes through from top to bottom, and a front thread trimming blade 22. The stitch start and drop needle hole 21 allows the needle to pass through. The movement of the thread trimming movable knife 20 can realize the movement of the stitch start and drop needle hole 21 to the position directly below the needle, and the movement of the front thread trimming blade 22 toward the first blade 11 until the two are engaged. The needle drop drive cam 31 and the stitch start and thread trimming cam 32 are both fixed on a rotatable shaft component in the sewing machine. The thread trimming cam crank 40 is rotatably and movably supported in the sewing machine base plate 90. The first roller 51 is rotatably mounted on the thread trimming cam crank 40. The first clutch drive source 71 is fixed to the sewing machine base plate 90 and acts on the thread trimming cam crank 40, pushing the thread trimming cam crank 40 to move in the left and right directions, so that the first roller 51 moves to the outer peripheral side of the needle drop drive cam 31, or moves away from the outer peripheral side of the needle drop drive cam 31. The second roller 52 is rotatably and movably mounted on the thread trimming cam crank 40. The second clutch drive source 72 is fixed to the thread trimming cam crank 40 and acts on the second roller 52, pushing the second roller 52 to move horizontally, thereby moving the second roller 52 to the outer periphery of the seam start thread trimming cam 32 or away from the outer periphery of the seam start thread trimming cam 32. The thread trimming cam crank 40 is in transmission connection with the thread trimming movable knife 20 via the thread trimming transmission assembly 60.

[0050] Furthermore, when the first clutch drive source 71 is not in operation, no power is transmitted between the first roller 51 and the needle drop drive cam 31 or the seam start and thread trimming cam 32; when the first clutch drive source 71 is in operation, it drives the first roller 51 to move to the outer peripheral side of the needle drop drive cam 31, and the first roller 51 can contact and cooperate with the needle drop drive cam 31. When the second clutch drive source 72 is not in operation, no power is transmitted between the second roller 52 and the needle drop drive cam 31 or the seam start and thread trimming cam 32; when the second clutch drive source 72 is in operation, it drives the second roller 52 to move to the outer peripheral side of the seam start and thread trimming cam 32, and the second roller 52 can contact and cooperate with the seam start and thread trimming cam 32.

[0051] The present application also provides a method for preventing bird nests from cutting when starting to sew, using the above-mentioned thread cutting mechanism of the sewing machine. The thread cutting mechanism of the sewing machine performs a waiting action before starting to sew. At this time, the first clutch driving source 71 remains in an inactive state, so that the first roller 51 and the needle drop driving cam 31 and the seam start thread cutting cam 32 have no power transmission; the second clutch driving source 72 remains in an inactive state, so that the second roller 52 and the needle drop driving cam 31 and the seam start thread cutting cam 32 have no power transmission; at this time, the first thread cutting knife 10 and the thread cutting movable knife 20 are both distributed on the front side of the needle, as shown in FIG. Figure 10 shown.

[0052] The seam-starting and bird-nest-preventing thread-cutting method involved in the present application comprises the following steps in sequence.

[0053] Step S1, before the sewing machine starts to sew the first stitch, or during the process of the needle moving down when the sewing machine starts to sew the first stitch, the sewing machine thread trimming mechanism performs the needle dropping action: the first clutch driving source 71 is actuated, and the second clutch driving source 72 is not actuated, the first clutch driving source 71 drives the thread trimming cam crank 40 to move in the left and right directions, so that the first roller 51 moves to the outer peripheral side of the needle dropping driving cam 31; as the first stitch is sewn, the shaft component of the sewing machine rotates, and the needle dropping driving cam 31 rotates along the shaft component on which it is located. The components rotate together. During this process, the needle drop driving cam 31 contacts and cooperates with the first roller 51. The needle drop driving cam 31 drives the thread trimming cam crank 40 to rotate through the first roller 51, and then drives the thread trimming movable knife 20 to move through the thread trimming transmission assembly 60. That is, the torque of the shaft component drives the thread trimming movable knife 20 to rotate backward through the needle drop driving cam 31, the first roller 51, the thread trimming cam crank 40 and the thread trimming transmission assembly 60 in sequence, so that the seam starting needle drop hole 21 is located directly below the needle. Figure 11 shown.

[0054] Step S2, the sewing machine moves down to start sewing the first needle, and the needle passes downward through the sewing start needle hole 21 on the thread trimming movable knife 20. Under the action of the rotary shuttle in the sewing machine, the upper thread end on one side of the needle is brought to the bottom of the thread trimming movable knife 20, that is, to the vicinity of the rotary shuttle.

[0055] Step S3, the sewing machine starts sewing and the first needle moves up. After the needle moves upward from the thread trimming movable knife 20, the first clutch drive source 71 is reset, and the thread trimming cam crank 40, the first roller 51 and the thread trimming movable knife 20 are reset respectively. The thread trimming movable knife 20 is reset to Figure 10 The standby state shown in the figure is as follows: during this process, the thread trimming knife 20 rotates forward to the front side of the needle, thereby extracting at least a portion of the upper thread end without interfering with the subsequent upward and downward movement of the needle. At this time, the first clutch drive source 71 is reset to the inactive state, and no power is transmitted to the first roller 51, the needle drop drive cam 31, and the seam start and thread trimming cam 32.

[0056] Step S4, the sewing machine starts sewing and sets the number of stitches N: the sewing machine starts sewing the second stitch, the third stitch, ..., until the Nth stitch.

[0057] 5. When the sewing machine starts sewing the Nth stitch, the thread trimming mechanism of the sewing machine performs the front thread trimming action: when the second clutch driving source 72 is in action and the first clutch driving source 71 is inactive, the second clutch driving source 72 drives the second roller 52 to move in the left and right directions, thereby driving the second roller 52 to move to the outer peripheral side of the thread trimming cam 32; as the Nth stitch is started, the thread trimming cam 32 rotates together with the shaft component on which it is located. During this process, the thread trimming cam 32 contacts and cooperates with the second roller 52, and the thread trimming cam 32 drives the thread trimming cam crank 40 to rotate through the second roller 52, and then drives the thread trimming movable knife 20 to move through the thread trimming transmission assembly 60, that is, the torque of the shaft component drives the thread trimming movable knife 20 to move through the thread trimming cam 32, the second roller 52, the thread trimming cam crank 40 and the thread trimming transmission assembly 60 in sequence, until the front thread trimming blade 22 engages with the first blade 11. Figure 12 As shown, the upper thread ends are cut off, thereby preventing the upper thread ends from being entangled and forming a bird's nest.

[0058] Step S6: The second clutch drive source 72 is reset, the thread trimming cam crank 40, the second roller 52 and the thread trimming movable knife 20 are reset, and the thread trimming movable knife 20 is reset to Figure 10 The waiting state is shown.

[0059] Therefore, the present application uses the first clutch drive source 71 to transmit power between the first roller 51 and the needle drop drive cam 31, so that the thread trimming movable knife 20 can extract a portion of the upper thread end to the needle plate bottom plate 90, and then pull the upper thread end to the back of the sewing material; and uses the second clutch drive source 72 to transmit power between the second roller 52 and the seam start thread trimming cam 32, so that the front thread trimming blade 22 and the first blade 11 can engage and cut the upper thread end, thereby effectively suppressing the formation of bird nests in the sewing material. In particular, the power for driving the thread trimming movable knife 20 in the present application is derived from the rotatable shaft component in the sewing machine, that is, from the existing power source in the sewing machine. There is no need to set up an additional motor to drive the thread trimming movable knife 20 to move, which meets the requirements of the thread trimming movable knife 20 moving at multiple positions required for reducing and preventing bird nests. At the same time, no additional power source is required, reducing the cost of the sewing machine. Therefore, the present invention can realize the anti-bird nest prevention of seams at low cost and reliably, and the thread ends are only on the back of the sewing material, ensuring that the stitches on the front of the sewing material are beautiful, and has strong versatility and can be applied to various sewing processes.

[0060] Furthermore, the first thread trimmer 10 is a fixed fixed knife fixed to the bottom surface of the sewing machine base plate 90. When the first clutch drive source 71 and the second clutch drive source 72 are not in operation, that is, when the sewing machine thread trimming mechanism is in a standby state, the first thread trimmer 10 and the movable thread trimmer 20 are located on the same side of the sewing machine needle, which is the front side.

[0061] Furthermore, the first clutch drive source 71 and the second clutch drive source 72 are preferably both electromagnets, and the cores of the respective electromagnets are both extended and retracted in the left-right direction. Figure 2 and Figure 3 As shown, the first clutch drive source 71 is disposed on the right side of the thread trimmer cam crank 40. The thread trimmer cam crank 40 comprises a crank shaft 41 extending leftward and rightward, a crank body 42 fixed to the crank shaft 41, a first crank arm 43 integrally extending from the right end of the crank body 42, and a second crank arm 44 integrally extending from the left end of the crank body 42. The crank shaft 41 is rotatably and movably supported in an axial hole of the sewing machine base 90. The first roller 51 is mounted on the outer end of the first crank arm 43. The electromagnet core of the first clutch drive source 71 is axially aligned with the crank shaft 41 and is located on the right side of the crank shaft 41. When the first clutch drive source 71 is not in operation, it is in a power-off state. When the first clutch drive source 71 is energized and in operation, its electromagnet core extends leftward, driving the thread trimmer cam crank 40 to move leftward, causing the first roller 51 to move to the outer periphery of the needle drop drive cam 31. The second roller 52 is mounted on the right side of the outer end of the second crank arm 44 so as to be movable left and right. The second clutch drive source 72 is an electromagnet fixed to the left side of the second crank arm 44. The electromagnet core of the second clutch drive source 72 is arranged opposite the second roller 52 and is located on the left side of the second roller 52. When the second clutch drive source 72 is not in operation, it is in a power-off state. When the second clutch drive source 72 is powered on, its electromagnet core extends to the right, driving the second roller 52 to move rightward, so that the second roller 52 moves to the outer periphery of the seam start and thread trimmer cam 32.

[0062] Furthermore, if Figure 2 and Figure 3 As shown, the thread trimming mechanism of the sewing machine involved in the present application also includes a second thread trimmer 80 disposed on the outer periphery of the lower shaft 110 of the sewing machine. The second thread trimmer 80 is also located behind the sewing machine needle. That is, the second thread trimmer 80 and the movable thread trimmer 20 are located on either side of the sewing machine needle in the front-to-back direction. The second thread trimmer 80 is provided with a second blade 81. The second thread trimmer 80 is used to cooperate with the movable thread trimmer 20 to perform post-thread trimming after sewing is completed. The second thread trimmer 80 can be a fixed fixed blade, in which case the sewing machine thread trimming mechanism has a single movable blade and two fixed blades; the second thread trimmer 80 can also be a movable movable blade, in which case the sewing machine thread trimming mechanism has a double movable blade and single fixed blade structure. In this embodiment, the second thread trimmer 80 is preferably a movable blade that can rotate about the lower shaft 110. Based on this, the thread trimming mechanism of the sewing machine also includes a rear thread trimming cam 33 and a stroke control electromagnet 73. The rear thread trimming cam 33 is fixed on a rotatable shaft component in the sewing machine. The rear thread trimming cam 33 is distributed on the left side of the needle drop drive cam 31. The second thread trimmer 80 is also connected to the thread trimming transmission assembly 60. The stroke control electromagnet 73 acts on the first clutch drive source 71. Figure 6As shown, the movable thread trimming knife 20 is further provided with a rear thread trimming blade 23, which is distributed in front of the front thread trimming blade 22, and the stitch starting and dropping holes 21 are distributed between the front thread trimming blade 22 and the rear thread trimming blade 23 in the front-to-back direction.

[0063] When the thread trimming mechanism of the sewing machine is in a waiting state, the stroke control electromagnet 73 and the first clutch drive source 71 are both powered off, and no power is transmitted between the first roller 51 and the rear thread trimming cam 33 and the needle drop drive cam 31. The second thread trimming knife 80 and the thread trimming movable knife 20 are distributed on both sides of the needle in the sewing machine. Figure 10 As shown. When the thread trimming mechanism of the sewing machine performs the needle drop action, the stroke control electromagnet 73 is powered off, but the first clutch drive source 71 is powered on. Only the first clutch drive source 71 drives the thread trimming cam crank 40 and the first roller 51 to move leftward by a distance of L1, so that the first roller 51 can transmit power to the needle drop drive cam 31. However, the first roller 51 and the rear thread trimming cam 33 are offset in the left and right directions and the two are disengaged. Therefore, there is still no power transmission between the first roller 51 and the rear thread trimming cam 33. The second thread trimming knife 80 and the thread trimming movable knife 20 are still distributed on both sides of the needle in the sewing machine, as shown. Figure 11 When the sewing machine thread trimming mechanism performs the front thread trimming action, the stroke control electromagnet 73 and the first clutch drive source 71 are both powered off, and no power is transmitted between the first roller 51 and the rear thread trimming cam 33 and the needle drop drive cam 31. When the thread trimming mechanism of the sewing machine performs the rear thread trimming action, the stroke control electromagnet 73 and the first clutch driving source 71 are energized, and the stroke control electromagnet 73 and the first clutch driving source 71 simultaneously drive the thread trimming cam crank 40 and the first roller 51 to move leftward, and the leftward movement distance is L2, L2 is greater than L1, so that the first roller 51 can transmit power to the rear thread trimming cam 33, but the first roller 51 and the needle drop driving cam 31 are staggered in the left and right directions and the two are disengaged, so that there is no power transmission between the first roller 51 and the needle drop driving cam 31; at this time, the rear thread trimming cam 33 drives the thread trimming cam crank 40 to rotate through the first roller 51, and then drives the thread trimming movable knife 20 and the second thread trimming knife 80 to move toward each other through the thread trimming transmission assembly 60, that is, the thread trimming movable knife 20 rotates backward, and the second thread trimming knife 80 rotates forward, so that the rear thread trimming blade 23 engages with the second blade 81, as shown in FIG. Figure 13 As shown, the upper thread is cut off, achieving the purpose of automatic thread trimming after sewing is completed.

[0064] Preferably, the connection structure between the stroke control electromagnet 73 and the first clutch drive source 71 is as follows: Figure 3 and Figure 4As shown, the sewing machine thread trimming mechanism further includes a fixed mounting plate 120 and a movable mounting plate 130. The fixed mounting plate 120 is secured to the bottom of the base plate 90 by several screws, and the stroke control electromagnet 73 is secured to the bottom of the fixed mounting plate 120. The movable mounting plate 130 is connected to the electromagnet core of the stroke control electromagnet 73, and the first clutch drive source 71 is secured to the movable mounting plate 130. When the stroke control electromagnet 73 is energized, its electromagnet core extends leftward, pulling the movable mounting plate 130 and the first clutch drive source 71 leftward. When the first clutch drive source 71 is energized, its electromagnet core also extends leftward. Therefore, the distance L1 by which the first roller 51 moves leftward when only the first clutch drive source 71 is energized is smaller than the distance L2 by which the first roller 51 moves leftward when both the stroke control electromagnet 73 and the first clutch drive source 71 are energized.

[0065] Furthermore, the structure of the thread cutting transmission assembly 60 is preferably as follows: Figure 4 and Figure 5 As shown, the left end of the thread trimming cam crank 40 is integrally provided with a third crank arm 45, and the third crank arm 45 is circumferentially staggered with the second crank arm 44; the thread trimming transmission assembly 60 includes a thread trimming slider 61 rotatably mounted at the outer end of the third crank arm 45, a thread trimming shaft 62 extending left and right and rotatably supported in the sewing machine bottom plate 90, a thread trimming crank 63 fixed to the left end of the thread trimming shaft 62, a thread trimming connecting rod 64, a first tool holder 65 rotatably mounted on the outer periphery of the lower shaft 110 through a shaft sleeve, and a thread trimming connecting rod 64. The second tool holder 68 and the trimmer transmission pin 69 fixed to the second tool holder 68, the right end of the trimmer shaft 62 is integrally provided with a shaft arm 621, and the shaft arm 621 is provided with a first trimmer slide 622 that slides and contacts with the trimmer slider 61, the two ends of the trimmer connecting rod 64 are hinged to the trimmer crank 63 and the first tool holder 65 respectively, the trimmer movable knife 20 is fixed to the first tool holder 65, the trimmer crank 63 is provided with a second trimmer slide 631 that slides and contacts with the trimmer transmission pin 69, and the second trimmer knife 80 is fixed to the second tool holder 68.

[0066] Preferably, if Figure 4 and Figure 5 As shown, the thread trimmer transmission assembly 60 also includes a first return torsion spring 66 and a second return torsion spring 67. The first return torsion spring 66 is sleeved on the thread trimmer shaft 62, and the two ends of the first return torsion spring 66 act on the thread trimmer crank 63 and the bottom plate 90 respectively. The sewing machine bottom plate 90 is provided with a support sleeve portion, and the second return torsion spring 67 is sleeved on the support sleeve portion. The two ends of the second return torsion spring 67 act on the thread trimmer cam crank 40 and the bottom plate 90 respectively. After the sewing machine thread trimmer mechanism performs the needle drop action, the spring force of the first return torsion spring 66 and the second return torsion spring 67 drives the thread trimmer crank 63 and the thread trimmer cam crank 40 to reset, thereby driving the various components in the thread trimmer transmission assembly 60 to reset.

[0067] Preferably, if Figure 4 As shown, a spring pin 610 is also fixed to the trimmer crank 63. This spring pin 610 comprises a pin housing fixed to the trimmer crank 63, a compression spring retained in the pin housing, and a positioning bead retractably mounted at the end of the pin housing facing the bottom surface of the base plate 90. The compression spring acts on the positioning bead. When the sewing machine's thread trimming mechanism is in a standby state, the positioning bead, under the action of the compression spring, abuts against the bottom surface of the base plate 90, reliably maintaining the active thread trimming blade 20 and the second thread trimming blade 80 in their respective stationary states.

[0068] Furthermore, if Figure 2 and Figure 3 As shown, the thread trimming mechanism of the sewing machine also includes an anti-jamming knife cam 34, which is fixed to a rotatable shaft component in the sewing machine. When the stroke control electromagnet 73 is powered off and the first clutch drive source 71 and the second clutch drive source 72 are both powered off, the second roller 52 is distributed on the outer peripheral side of the anti-jamming knife cam 34 and can contact and cooperate with the anti-jamming knife cam 34. In this way, after the sewing machine thread trimming mechanism performs the post-thread trimming action, the thread trimming movable knife 20 and the second thread trimming knife 80 are stuck in the Figure 13 When the sewing machine sews the last stitch, the shaft component drives the anti-jamming knife cam 34 to rotate, and the anti-jamming knife cam 34 pushes the trimming cam crank 40 to reset through the second roller 52. The trimming cam crank 40 is pushed in the reverse direction to release the stuck state and then reset to Figure 10 status.

[0069] Furthermore, the present application realizes anti-bird nest thread trimming at the start of sewing and normal thread trimming after the end of sewing by setting a needle drop drive cam 31, a thread trimming cam 32 at the start of sewing, a rear thread trimming cam 33 and an anti-jamming knife cam 34 fixed on an existing rotating shaft component in the sewing machine. The needle drop drive cam 31, the rear thread trimming cam 33, the thread trimming cam 32 at the start of sewing and the anti-jamming knife cam 34 are arranged in sequence from right to left. The needle drop drive cam 31, the rear thread trimming cam 33, the thread trimming cam 32 at the start of sewing and the anti-jamming knife cam 34 can be fixed on the same shaft component or on different shaft components. The four cams of the needle drop drive cam 31, the rear thread trimming cam 33, the thread trimming cam 32 at the start of sewing and the anti-jamming knife cam 34 can be four independent cams or can be integrated into one thread trimming drive cam 30. In this embodiment, if Figure 2 and Figure 3 ,as well as Figure 7 and Figure 8As shown, the needle drop drive cam 31, the seam start and thread trimming cam 32, the rear thread trimming cam 33 and the anti-jamming knife cam 34 are integrated into a thread trimming drive cam 30. The thread trimming drive cam 30 has four cam parts, which respectively constitute the needle drop drive cam 31, the rear thread trimming cam 33, the seam start and thread trimming cam 32 and the anti-jamming knife cam 34 from right to left. The thread trimming drive cam 30 is fixed and locked on the lower shaft 110 by screws. Of course, in other embodiments, the thread trimming drive cam 30 is fixed and locked on the tooth lifting shaft or the feed shaft by screws.

[0070] The present application improves the profile of the peripheral cam surface of the four cam parts on the thread trimming drive cam 30, and controls the feed amount of the thread trimming cam crank 40 through the three electromagnets of the stroke control electromagnet 73, the first clutch drive source 71 and the second clutch drive source 72, so that the first roller 51 and the second roller 52 cooperate with the different cam surfaces on the thread trimming drive cam 30, so that the thread trimming movable knife 20 and the second thread trimming knife 80 have multiple motion trajectories, especially the thread trimming movable knife 20 rotates to multiple different positions, meeting the requirements of the thread trimming movable knife 20 for multiple movement positions required for front thread trimming when starting to sew to prevent bird nests and rear thread trimming when sewing is completed, while also eliminating the need for an additional power source, reducing costs. In this embodiment, the rotation angle relationship between the thread trimming cam crank 40 and the thread trimming drive cam 30 in the cooperative state is as follows: Figure 9 As shown, Figure 9 In the figure, curve P1 is the rotation angle relationship diagram between the thread trimming cam crank 40 and the needle drop driving cam 31, curve P2 is the rotation angle relationship diagram between the thread trimming cam crank 40 and the seam starting thread trimming cam 32, curve P3 is the rotation angle relationship diagram between the thread trimming cam crank 40 and the rear thread trimming cam 33, and curve P4 is the rotation angle relationship diagram between the thread trimming cam crank 40 and the anti-jamming knife cam 34.

[0071] In summary, the working principle of the sewing machine thread trimming mechanism involved in this application is as follows.

[0072] 1. The execution logic of the front thread trimming function is as follows: after the sewing machine is started, the waiting action, needle drop action and front thread trimming action are executed in sequence. The execution process of each action is as follows.

[0073] 1.1. Waiting action: The stroke control electromagnet 73, the first clutch drive source 71 and the second clutch drive source 72 are all powered off, the first roller 51 is disengaged from the thread trimming drive cam 30, the second roller 52 is distributed on the outer periphery of the anti-jamming cam 34 of the thread trimming drive cam 30, and the spring pin 610 is in contact with the bottom surface of the bottom plate 90; at this time, Figure 10 As shown, the front thread trimming movable knife 20 is in a stationary state and is distributed on the front side of the needle together with the first thread trimming knife 10, and the second thread trimming knife 80 is in a stationary state and is distributed on the rear side of the needle.

[0074] 1.2 Needle drop action: The main motor of the sewing machine drives the main shaft to rotate, and the main shaft can be decelerated when the first stitch is sewn; when the lower shaft 110 rotates to a certain angle, the first clutch drive source 71 is energized, and the first roller 51 cooperates with the needle drop drive cam 31 to drive the thread trimming cam crank 40 to rotate, and the needle drop drive cam 31 and the thread trimming cam crank 40 press Figure 9 The curve P1 in the figure drives the thread trimming movable knife 20 to rotate backward until the sewing needle hole 21 is located directly below the needle. Figure 11 In the horizontal straight line section of the curve P1, the thread trimming movable knife 20 always keeps Figure 11 After passing the horizontal straight line section of the curve P1, the first clutch drive source 71 is powered off, the first roller 51 is disengaged from the thread trimming drive cam 30, and the thread trimming movable knife 20 rotates forward and resets to Figure 10 , pull out a portion of the upper thread end to under the needle plate.

[0075] 1.3. Front thread trimming action: After setting the number of stitches at the start of sewing, the main shaft can be decelerated; when the lower shaft 110 rotates to a certain angle, the second clutch drive source 72 is energized, the second roller 52 cooperates with the sewing thread trimming cam 32, driving the thread trimming cam crank 40 to rotate, and the sewing thread trimming cam 32 and the thread trimming cam crank 40 press Figure 9 The curve P2 in the figure moves, when the thread trimming cam 32 exceeds the Figure 10 When the angle of the thread trimming cam crank 40 is in the state, the thread trimming cam crank 40 is pushed in the opposite direction by the seam trimming cam 32, and the thread trimming movable knife 20 rotates forward; at the highest point of the curve P2, the thread trimming movable knife 20 engages with the first thread trimming knife 10, as shown in FIG. Figure 12 As shown, the front thread trimming action is realized; the cut upper thread ends are sucked away by the negative pressure suction device. After the front thread trimming is completed, the second clutch drive source 72 is immediately powered off, and the thread trimming movable knife 20 rotates backward and resets to Figure 10 location.

[0076] 2. The sewing machine sews normally.

[0077] 3. Execution of the rear thread trimming action at the end of sewing: When the lower shaft 110 rotates to a certain angle, the stroke control electromagnet 73 and the first clutch drive source 71 are energized, the first roller 51 cooperates with the rear thread trimming cam 33 to drive the thread trimming cam crank 40 to rotate, and the rear thread trimming cam 33 and the thread trimming cam crank 40 press Figure 9 The curve P3 in the movement drives the thread trimming movable knife 20 to rotate backward and drives the second thread trimming knife 80 to rotate forward; at the highest point of the curve P3, the thread trimming movable knife 20 engages with the second thread trimming knife 80, as shown Figure 13 After the rear trimming is completed, the stroke control electromagnet 73 and the first clutch drive source 71 are immediately powered off, and the trimming movable knife 20 rotates forward and resets to Figure 10The second thread cutter 80 rotates backward and returns to the position Figure 10 location.

[0078] 4. After the rear trimming is completed, the anti-stuck knife action is executed: When the rear trimming is completed, the stroke control electromagnet 73, the first clutch drive source 71 and the second clutch drive source 72 are all in the power-off state, and the second roller 52 is distributed on the outer peripheral side of the anti-stuck knife cam 34. If the thread trimming movable knife 20 and the second thread trimming knife 80 are stuck in the Figure 13 Position, then in the process of sewing the last stitch of the lower shaft 110 rotating, when the anti-jamming knife cam 34 exceeds the curve of the rear thread trimming cam 33, as shown Figure 9 As shown in the curve P4 in FIG, the anti-stuck knife cam 34 pushes the trimming cam crank 40 in the reverse direction, releasing the stuck state of the trimming movable knife 20 and the second trimming knife 80, so that the trimming movable knife 20 and the second trimming knife 80 are reset to Figure 10 location.

[0079] In summary, the present invention effectively overcomes various shortcomings of the prior art and has high industrial utilization value.

[0080] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A thread trimming mechanism for a sewing machine, comprising a first thread trimming knife (10) and a movable thread trimming knife (20) provided on the outer peripheral side of a lower shaft (110) of the sewing machine, wherein the first thread trimming knife (10) is provided with a first blade (11) and is a fixed fixed knife, and the movable thread trimming knife (20) is provided with a through-hole for starting and dropping a sewing needle (21) and a front thread trimming blade (22), characterized in that: The invention also includes a needle drop driving cam (31), a seam start and thread trimming cam (32), a thread trimming cam crank (40) rotatably and movably supported in a sewing machine bottom plate (90), a first roller (51) mounted on the thread trimming cam crank (40), a second roller (52) movably mounted on the thread trimming cam crank (40), a thread trimming transmission assembly (60), a first clutch driving source (71), a second clutch driving source (72), a rear thread trimming cam (33), an anti-jamming knife cam (34), a second thread trimming knife (80) provided on the outer peripheral side of the lower shaft (110) of the sewing machine and movable, and a stroke control electromagnet (73). The needle drop driving cam (31) and the seam start and thread trimming cam (32) are both fixed on a rotatable shaft component in the sewing machine. The first clutch driving source (71) ) is fixed to the sewing machine bottom plate (90) and acts on the thread trimming cam crank (40), the second clutch drive source (72) is fixed to the thread trimming cam crank (40) and acts on the second roller (52), the thread trimming cam crank (40) is connected to the thread trimming movable knife (20) through the thread trimming transmission assembly (60); the rear thread trimming cam (33) is fixed to a rotatable shaft component in the sewing machine, the anti-stuck knife cam (34) is fixed to a rotatable shaft component in the sewing machine, the thread trimming movable knife (20) is provided with a rear thread trimming blade (23), the second thread trimming knife (80) is provided with a second blade (81), the second thread trimming knife (80) is connected to the thread trimming transmission assembly (60), and the stroke control electromagnet (73) acts on the first clutch drive source (71); When the first clutch drive source (71) is not in operation, no power is transmitted between the first roller (51) and the needle drop drive cam (31) and the seam start and thread trimming cam (32); when the first clutch drive source (71) is in operation, the first roller (51) can contact and cooperate with the needle drop drive cam (31); When the second clutch drive source (72) is not in operation, no power is transmitted between the second roller (52) and the needle drop drive cam (31) and the seam start and thread trimming cam (32); when the second clutch drive source (72) is in operation, the second roller (52) can contact and cooperate with the seam start and thread trimming cam (32); When the first clutch drive source (71) and the second clutch drive source (72) are not in operation, the first thread trimmer (10) and the thread trimmer movable knife (20) are distributed on the same side of the needle in the sewing machine; When the stroke control electromagnet (73) is powered off and the first clutch drive source (71) is inactive, no power is transmitted between the first roller (51) and the rear thread trimming cam (33), and the second thread trimming knife (80) and the thread trimming movable knife (20) are distributed on both sides of the needle in the sewing machine; When the stroke control electromagnet (73) is energized and the first clutch drive source (71) is activated, the first roller (51) can contact and cooperate with the rear thread trimming cam (33), and drive the thread trimming movable knife (20) and the second thread trimming knife (80) to move toward each other through the thread trimming cam crank (40) and the thread trimming transmission assembly (60), so that the rear thread trimming blade (23) is engaged with the second blade (81); When the stroke control electromagnet (73) is powered off and both the first clutch drive source (71) and the second clutch drive source (72) are inactive, the second roller (52) is distributed on the outer peripheral side of the anti-knife jam cam (34) and can contact and cooperate with the anti-knife jam cam (34).

2. The thread trimming mechanism for a sewing machine according to claim 1, characterized in that: The shaft component is a lower shaft (110) or a tooth-lifting shaft or a feeding shaft of a sewing machine.

3. The thread trimming mechanism for a sewing machine according to claim 1, characterized in that: The first clutch drive source (71) is an electromagnet, the thread trimming cam crank (40) has a crank shaft (41), a crank body (42) fixed to the crank shaft (41), and a first crank arm (43) and a second crank arm (44) extending integrally from the crank body (42), the crank shaft (41) is rotatably and movably supported in the sewing machine base (90), the electromagnet core of the first clutch drive source (71) is axially opposite to the crank shaft (41), the first roller (51) is mounted on the first crank arm (43), the second roller (52) is movably mounted on the second crank arm (44), the second clutch drive source (72) is an electromagnet fixed to the second crank arm (44), and the electromagnet core of the second clutch drive source (72) is axially opposite to the second roller (52).

4. The thread trimming mechanism for a sewing machine according to claim 1, characterized in that: The thread trimming cam crank (40) is fixed with a third crank arm (45), and the thread trimming transmission assembly (60) includes a thread trimming slider (61) rotatably mounted on the third crank arm (45), a thread trimming shaft (62) rotatably supported in the sewing machine bottom plate (90), a thread trimming crank (63) fixed at one end of the thread trimming shaft (62), a thread trimming connecting rod (64), and a first knife holder (65) rotatably assembled on the outer periphery of the lower shaft (110), the other end of the thread trimming shaft (62) is integrally provided with a shaft arm (621), and the shaft arm (621) is provided with a first thread trimming slot (622) that is slidably matched with the thread trimming slider (61) and in surface contact, the two ends of the thread trimming connecting rod (64) are respectively hinged to the thread trimming crank (63) and the first knife holder (65), and the thread trimming movable knife (20) is fixed to the first knife holder (65).

5. The thread trimming mechanism for a sewing machine according to claim 4, characterized in that: The thread trimmer transmission assembly (60) further comprises a first return torsion spring (66) and a second return torsion spring (67), wherein the first return torsion spring (66) is sleeved on the thread trimmer shaft (62) and acts on the thread trimmer crank (63), a support sleeve is provided on the sewing machine bottom plate (90), and the second return torsion spring (67) is sleeved on the support sleeve and acts on the thread trimmer cam crank (40).

6. The thread trimming mechanism for a sewing machine according to claim 1, characterized in that: The thread trimming cam crank (40) is fixedly provided with a third crank arm (45), and the thread trimming transmission assembly (60) includes a thread trimming slider (61) rotatably mounted on the third crank arm (45), a thread trimming shaft (62) rotatably supported in a sewing machine bottom plate (90), a thread trimming crank (63) fixed to one end of the thread trimming shaft (62), a thread trimming connecting rod (64), a first knife holder (65) rotatably mounted on the outer periphery of the lower shaft (110), a second knife holder (68) rotatably mounted on the outer periphery of the lower shaft (110), and a thread trimming transmission pin (69) fixed to the second knife holder (68). The other end of the thread trimming shaft (62) is integrally provided with a shaft arm (621), and the shaft arm (621) is provided with a first thread trimming slot (622) that is in sliding engagement with the thread trimming slider (61) and in surface contact engagement. The two ends of the thread trimming connecting rod (64) are respectively hinged to the thread trimming crank (63) and the first tool holder (65). The thread trimming movable knife (20) is fixed to the first tool holder (65). The thread trimming crank (63) is provided with a second thread trimming slot (631) that is in sliding engagement with the thread trimming transmission pin (69). The second thread trimming knife (80) is fixed to the second tool holder (68).

7. The thread trimming mechanism for a sewing machine according to claim 1, characterized in that: The needle drop driving cam (31), the seam start thread trimming cam (32), the rear thread trimming cam (33) and the anti-stuck knife cam (34) are integrated into a thread trimming driving cam (30).

8. A method for preventing bird nests from cutting seams, characterized by: Using the sewing machine thread trimming mechanism according to claim 1, the seam starter and bird nest prevention thread trimming method comprises the following steps in sequence: S1. Before the sewing machine starts sewing the first stitch, or during the process of the needle moving downward when the sewing machine starts sewing the first stitch, the first clutch drive source (71) is activated and the second clutch drive source (72) is not activated. The first clutch drive source (71) drives the thread trimming cam crank (40) to move, so that the first roller (51) moves to the outer peripheral side of the needle drop drive cam (31). The shaft component of the sewing machine drives the needle drop drive cam (31) to rotate, and drives the thread trimming movable knife (20) to move through the first roller (51), the thread trimming cam crank (40) and the thread trimming transmission assembly (60), so that the stitch start and needle drop hole (21) is located directly below the needle. S2, the sewing machine's first needle moves downward, the needle passes through the sewing start needle hole (21), and under the action of the rotary hook in the sewing machine, the upper thread end on one side of the needle is brought to the bottom of the thread trimming movable knife (20); S3, the first needle of the sewing machine moves upward, the first clutch drive source (71) is reset, the thread trimming cam crank (40), the first roller (51) and the thread trimming movable knife (20) are reset, the thread trimming movable knife (20) extracts at least a part of the upper thread end, and the first roller (51) and the needle drop drive cam (31) and the sewing start thread trimming cam (32) are all without power transmission; S4, setting the number of stitches for sewing machine to start sewing; S5, the second clutch drive source (72) is activated and the first clutch drive source (71) is not activated, the second clutch drive source (72) drives the second roller (52) to move to the outer peripheral side of the seam start and thread trimming cam (32), the shaft component of the sewing machine drives the seam start and thread trimming cam (32) to rotate, and drives the thread trimming movable knife (20) to move through the second roller (52), the thread trimming cam crank (40) and the thread trimming transmission assembly (60) until the front thread trimming blade (22) engages with the first blade (11) to cut the upper thread end; S6. The second clutch drive source (72) is reset, and the thread trimming cam crank (40), the second roller (52), and the thread trimming movable knife (20) are reset.

9. A sewing machine, characterized in that: The sewing machine is equipped with the sewing machine thread trimming mechanism according to any one of claims 1 to 7.

Images