Thread trimming structure of sewing machine

Abstract

The utility model provides a thread trimming structure of a sewing machine, and belongs to the technical field of sewing machines. The problem that an existing thread trimming structure is insufficient in anti-bird groove effect is solved. The thread trimming structure of the sewing machine comprises an auxiliary cutter arranged below a needle plate and a movable cutter with a movable cutter edge, a driving shaft, a movable cutter connecting rod assembly connected with the movable cutter, an auxiliary cutter connecting rod assembly connected with the auxiliary cutter, a movable cutter cam and an auxiliary cutter cam, the movable cutter cam and the auxiliary cutter cam are arranged in parallel at an interval and are fixedly connected to the driving shaft, and the movable cutter connecting rod assembly is provided with an abutting part I abutting against the working circumferential surface of the movable cutter cam; the working circumferential surface of the moving cutter cam comprises a first concave arc section AB, a first convex arc section BC, a second concave arc section CD and a second convex arc section DA which are sequentially connected end to end. According to the utility model, the needle-starting upper thread remaining on the cloth can be shortened, so that a better bird nest prevention effect is achieved.

Description

Technical Field

[0001] This utility model belongs to the field of sewing machine technology and relates to a thread-cutting structure for a sewing machine. Background Technology

[0002] A sewing machine is a device that uses one or more threads to create one or more stitches on fabric, allowing two or more layers of fabric to interweave or sew together. To improve sewing efficiency, sewing machines are usually equipped with a thread-cutting mechanism. This mechanism automatically cuts off the starting thread left on the fabric at the beginning of the sewing stitch; otherwise, long thread ends will remain, forming clumps and creating an unsightly "bird's nest" effect. After the last stitch is completed, the tail thread and bobbin thread also need to be cut.

[0003] Existing thread-cutting structures in sewing machines, such as the thread-cutting method of the double-moving-blade thread-cutting mechanism disclosed in patent literature (application number: 202411329869.0), include a first thread-cutting blade and a second thread-cutting blade. The first and second rings are respectively mounted on a first ring and a second ring, which are rotatably mounted on the sewing machine base, allowing the first and second thread-cutting blades to rotate around their respective centers. The thread is cut when the first and second thread-cutting blades approach each other. However, this thread-cutting structure has the following shortcomings in practical use:

[0004] 1. When it is necessary to cut the starting thread, the first cutting blade engages with the second cutting blade as it retracts from the second position (swinging upwards to the position below the needle) to cut the starting thread. The cutting position of this cutting structure is relatively far from the needle hole on the needle plate, resulting in a longer distance between the cut end of the thread and the fabric, meaning a longer starting thread tail remains on the fabric, leading to poor bird's nest prevention.

[0005] 2. This design employs a second transmission rod sleeved outside the first transmission rod. A first driving component and a second driving component respectively drive the first and second transmission rods to rotate, which in turn drives the first and second wire-cutting blades to swing up and down. In other words, this wire-cutting structure uses two motors to drive the first and second wire-cutting blades to swing. Since the two motors operate independently, they require more complex control algorithms to coordinate the operation of the first and second wire-cutting blades. This complexity increases the risk of potential malfunctions and can easily lead to changes in the coordination between the two blades, thus affecting the stability and reliability of the wire-cutting operation. Summary of the Invention

[0006] The purpose of this invention is to address the aforementioned problems in existing technologies by proposing a thread-cutting structure for sewing machines. This invention solves the problem of insufficient bird-proofing effect of existing thread-cutting structures and improves the working stability of the thread-cutting structure.

[0007] The objective of this utility model can be achieved through the following technical solution: a thread-cutting structure for a sewing machine, the sewing machine including a machine base and a needle plate with needle holes, the thread-cutting structure including an auxiliary knife and a movable knife with a moving blade edge, both disposed below the needle plate, the machine base also being provided with a drive shaft, a movable knife linkage assembly connected to the movable knife, and an auxiliary knife linkage assembly connected to the auxiliary knife, characterized in that the thread-cutting structure further includes a movable knife cam and an auxiliary knife cam, the movable knife cam and the auxiliary knife cam being arranged in parallel and spaced apart and both fixedly connected to the drive shaft, the movable knife linkage assembly having a contacting part that abuts against the working circumferential surface of the movable knife cam;

[0008] The working circumferential surface of the moving cam includes a first concave arc segment AB, a first convex arc segment BC, a second concave arc segment CD, and a second convex arc segment DA connected end to end in sequence. The first convex arc segment BC has a shearing arc surface concentric with the drive shaft.

[0009] As the shearing arc surface on the moving blade cam slides past the abutment part, the moving blade stops at a position where its cutting edge is directly below the needle drop hole. During this process, the auxiliary blade cam can drive the auxiliary blade to move towards the cutting edge of the moving blade through the auxiliary blade linkage assembly and engage with the cutting edge of the moving blade.

[0010] In this wire shearing structure, since both the moving blade cam and the auxiliary blade cam are fixedly connected to the drive shaft, they can be driven to rotate by a single motor. This eliminates the potential error accumulation between the two motors when driven separately, simplifies the control algorithm, and makes the movements of the moving blade and the auxiliary blade more coordinated, thereby improving the working stability and reliability of the wire shearing structure.

[0011] As a further improvement, this thread-cutting structure also includes a thread-cutting arc surface concentric with the drive shaft on the first convex arc segment BC. Since the distance between the abutment part and the drive shaft (or the rotation center of the moving blade cam) remains unchanged as the thread-cutting arc surface slides past the abutment part, the moving blade remains stationary during this process. Therefore, this thread-cutting arc surface design allows the moving blade to remain stationary while the auxiliary blade cam rotates and moves towards the moving blade for thread cutting. Even though the moving blade cam must rotate with the drive shaft, the moving blade remains stationary, waiting for the auxiliary blade to approach and cut the thread. Compared to the case where both the moving blade and the auxiliary blade move and engage, this thread-cutting method uses a "one stationary, one moving" approach, which more precisely controls the thread-cutting position below the needle hole on the needle plate, thus bringing the thread-cutting position closer to the needle hole and minimizing the amount of thread remaining on the fabric, thereby achieving a better anti-bird's nest effect.

[0012] Furthermore, since the position of the moving blade is directly controlled by the shape of the moving blade cam, the presence of a wire-cutting arc surface concentric with the drive shaft on the moving blade cam ensures that even slight errors in the rotation angle of the motor driving the drive shaft will not affect the final position of the moving blade, guaranteeing that the moving blade is always positioned directly below the needle hole, awaiting wire cutting. In contrast, if the motor directly drives the moving blade via a connecting rod, the motor's rotation angle error will be directly transmitted to the moving blade. Therefore, any slight error will cause a change in the moving blade's position, making it impossible to guarantee that the engagement position of the moving blade and the auxiliary blade is always directly below the needle hole. Thus, the wire-cutting method of this invention can tolerate certain motor errors without affecting the precise wire-cutting position, thereby more accurately controlling the wire-cutting position below the needle hole on the needle plate, achieving a better anti-bird's nest effect.

[0013] During sewing, the drive shaft drives the moving cutter cam to rotate clockwise in a unidirectional cycle, causing the first concave arc segment AB, the first convex arc segment BC, the second concave arc segment CD, and the second convex arc segment DA to slide sequentially over the abutment part. The auxiliary cutter cam and the moving cutter cam rotate synchronously and in the same direction. Because the working circumference of the moving cutter cam includes the first concave arc segment AB, the first convex arc segment BC, the second concave arc segment CD, and the second convex arc segment DA connected end-to-end, the design of this working circumference allows the moving cutter to swing up and down twice during one rotation of the moving cutter cam. This allows the drive shaft to drive the moving cutter cam to rotate one full rotation, effectively cutting the starting thread and simultaneously cutting the end thread and bobbin thread after sewing.

[0014] In the thread-cutting structure of the sewing machine described above, the sewing machine also includes a rotary hook. The moving blade swings up and down around the outer periphery of the rotary hook. When the working circumferential surface of the moving blade cam pushes against the abutment in a direction away from the drive shaft axis, the moving blade swings downward. This thread-cutting structure also includes a pressure plate located next to the rotary hook. When the starting point B of the first convex arc segment BC abuts against the abutment, the moving blade swings downward to the lowest point and the lower side of the moving blade abuts against the pressure plate. After the first stitch is inserted and the needle is lifted, the moving blade swings downwards with the starting thread until the starting point B of the first convex arc segment BC comes into contact with the abutment. At this point, the moving blade swings to the lower stop point (the lowest point). At this position, the lower side of the moving blade can abut against the pressure plate, clamping the thread (the starting thread) that passes through the lower needle hole. This allows the starting thread to be positioned, preventing it from flying around and facilitating a clean and efficient thread-cutting action by the moving blade and the auxiliary blade, thus avoiding thread-cutting failure.

[0015] In the thread-cutting structure of the sewing machine described above, a suction pipe is also provided beside the pressure plate. When the moving blade swings upward, it can detach from the pressure plate. Before cutting the starting thread, the suction pipe is already in suction mode. Since the moving blade can detach from the pressure plate after swinging upward, the thread end will be directly sucked away by the suction pipe after the starting thread is cut, avoiding the situation where the thread end is scattered everywhere.

[0016] In the thread-cutting structure of the sewing machine described above, the auxiliary knife connecting rod assembly has a second abutting part that abuts against the working circumferential surface of the auxiliary knife cam. The working circumferential surface of the auxiliary knife cam (9) has a starting needle thread-cutting tip a and a tail needle thread-cutting tip c arranged sequentially along the circumferential direction. The distance from the starting needle thread-cutting tip a and the tail needle thread-cutting tip c to the center of the drive shaft is greater than the distance from the other surfaces to the center of the drive shaft.

[0017] As the wire-cutting arc surface on the moving blade cam slides past the first abutment, the starting wire-cutting tip a on the auxiliary blade cam can slide past the second abutment, causing the auxiliary blade to move toward the moving blade edge and engage with the moving blade edge.

[0018] As the second convex arc segment DA on the moving blade cam slides past the first abutment, the tail needle cutting tip c on the auxiliary blade cam can slide past the second abutment, causing the auxiliary blade to move toward the moving blade edge and engage with the moving blade edge.

[0019] Because the distances from the starting thread cutting tip (a) and the ending thread cutting tip (c) on the working surface of the auxiliary knife cam to the drive shaft center are greater than the distances from other surfaces to the drive shaft center, the auxiliary knife cam also has two movements of approaching and then moving away from the moving knife when it rotates one revolution. This causes the drive shaft to drive the moving knife cam and the auxiliary knife cam to rotate one revolution, thus achieving the cutting of the starting thread and simultaneously cutting the ending thread and the bobbin thread after sewing. Specifically:

[0020] As the shearing arc surface on the moving blade cam slides past the first abutment, the starting shearing tip a on the auxiliary blade cam slides past the second abutment, causing the auxiliary blade to move toward the moving blade edge and engage with the moving blade edge, thus cutting the starting shearing thread.

[0021] As the second convex arc segment DA on the moving blade cam slides past the first abutment, the tail needle cutting tip c on the auxiliary blade cam slides past the second abutment, causing the auxiliary blade to move toward the moving blade edge and engage with the moving blade edge, cutting off the tail needle face thread and bottom thread.

[0022] In the thread-cutting structure of the sewing machine described above, the second convex arc segment DA is an arc surface concentric with the drive shaft, and the distances from the starting needle thread-cutting tip a and the ending needle thread-cutting tip c to the center of the drive shaft are equal. This structure ensures that the auxiliary blade swings to the same position during both the starting needle thread-cutting and the ending needle thread-cutting. Simultaneously, because the second convex arc segment DA is an arc surface concentric with the drive shaft, as the second convex arc segment DA slides past the abutment part, the moving blade will stop at a position where its cutting edge is directly below the needle hole, and the auxiliary blade can also move to a position where it engages with the cutting edge of the moving blade. This makes the thread-cutting position closer to the needle hole, ensuring that the cut end needle thread and bottom thread are as short as possible after sewing, improving the "bird's nest" effect.

[0023] In the thread-cutting structure of the sewing machine described above, the moving blade also has a lower needle hole. The blade edge of the moving blade is located in front of the lower needle hole along the swing direction of the moving blade. The distance from the starting point B and the ending point C of the first convex arc segment BC to the center of the drive shaft is greater than the distance from the thread-cutting arc surface to the center of the drive shaft. When the concave inflection point of the first concave arc segment AB abuts against the abutting part, the lower needle hole on the moving blade and the needle drop hole on the needle plate are vertically aligned.

[0024] Before the first needle is inserted, the drive shaft drives the moving knife cam to rotate to the concave inflection point of the first concave arc segment AB and abut against the abutment part. At this time, the needle hole on the moving knife and the needle drop hole on the needle plate are directly aligned. The needle first passes through the needle hole downwards, then leaves the needle hole upwards and is lifted above the needle plate, completing the first needle insertion action. The surface thread on the needle remains inside the needle hole.

[0025] Then, the drive shaft drives the moving cutter cam to rotate. At this time, the first concave arc segment AB will push the abutment part to move away from the drive shaft axis, causing the moving cutter to swing downward with the starting thread until the starting point B of the first convex arc segment BC abuts against the abutment part. At this time, since the distance from the starting point B to the drive shaft axis is greater than the distance from the cutting arc surface to the drive shaft axis, the position of the moving cutter is lower than the position of the thread to be cut. The moving cutter can avoid the needle's down-needle position, so that the needle will not hit the moving cutter when it goes down.

[0026] Afterward, the needle performs the second stitch, locking the top thread on the needle with the bottom thread in the rotary hook mechanism. Once the needle has been sewn to the set number of stitches, such as two, three, or four, the drive shaft drives the moving blade to continue oscillating. When the thread-cutting arc surface on the first convex segment BC abuts against the abutment, the moving blade stops at a position where its cutting edge is directly below the needle hole. At this point, the auxiliary blade moves towards the cutting edge and engages with it, thus cutting the top thread.

[0027] After the thread is cut, the drive shaft continues to drive the moving knife cam to rotate until the end point C of the first convex arc segment BC abuts against the abutment part. At this time, since the distance from the end point C to the center of the drive shaft is also greater than the distance from the thread-cutting arc surface to the center of the drive shaft, the moving knife swings downward from the thread-cutting position during this process, so that the moving knife can avoid the needle's down-needle position, so that the needle will not hit the moving knife, and the sewing machine can continue to perform subsequent sewing until the last stitch is completed.

[0028] In the thread-cutting structure of the sewing machine described above, the moving blade also has a hook groove located between the blade edge and the lower needle hole. When the concave inflection point of the second concave arc segment CD abuts against the abutting part, the hook groove on the moving blade is vertically aligned with the needle drop hole on the needle plate.

[0029] After the last stitch is completed, the drive shaft rotates the moving knife cam. As the moving knife cam moves from the end point C of the first convex arc segment BC to the concave inflection point of the second concave arc segment CD, the moving knife swings upward and uses the thread-separating tip at the front of the moving knife to push one of the needle thread loops of the bobbin thread and the top thread towards the side of the thread-separating tip. As the moving knife continues to swing upward, the needle thread and the bobbin thread slide along the side wall of the moving knife until the concave inflection point of the second concave arc segment CD comes into contact with the abutment. At this point, the hook groove on the moving knife is aligned vertically with the needle drop hole on the needle plate, and the needle thread and the bobbin thread can smoothly enter the hook groove. Subsequently, as the moving cam continues to rotate, the moving cam moves from the concave inflection point of the second concave arc segment CD to the starting point D of the second convex arc segment DA along the abutment part. During this process, the moving cam swings downward, causing the moving blade edge to move closer to the bottom of the needle hole. At the same time, the moving blade edge moves closer to the tail needle face line and bottom line, making it easier for the auxiliary knife to approach and cut the tail needle face line and bottom line.

[0030] In the thread-cutting structure of the sewing machine described above, the length of the second convex arc segment DA is less than the length of the first convex arc segment BC. Since the moving blade remains stationary as the second convex arc segment DA slides past the abutment part, its function is solely to cut the top and bottom threads of the needle. At this point, the shorter length of the second convex arc segment DA compared to the first convex arc segment BC allows the moving blade to quickly return to its initial state after the sewing work is completed and the top and bottom threads are cut, ready for the next sewing operation. This improves thread-cutting efficiency and the overall efficiency of the sewing machine.

[0031] In the thread-cutting structure of the sewing machine described above, the auxiliary knife swings up and down around the outer periphery of the rotary hook above the pressure plate, and the auxiliary knife swings upward when the working circumferential surface of the auxiliary knife cam pushes against the abutment in a direction away from the axis of the drive shaft; the working circumferential surface of the auxiliary knife cam also has a thread-cutting tip b, a starting needle thread-cutting tip a, a thread-cutting tip b, and a tail needle thread-cutting tip c arranged sequentially along the working circumferential surface of the auxiliary knife cam.

[0032] As the second convex arc segment DA on the moving blade cam slides past the first abutment, the tail needle cutting tip c on the auxiliary blade cam can slide past the second abutment, causing the auxiliary blade to move towards the moving blade's cutting edge and engage with it, cutting the tail needle's surface thread and bottom thread. Therefore, before cutting the tail needle's surface thread and bottom thread, the thread-to-be-cutting tip b will slide past the second abutment, allowing the auxiliary blade to move closer to the cutting position beforehand, rather than instantly approaching the moving blade from a great distance. This design improves the auxiliary blade's cutting stability, enhances the cutting effect, and avoids uneven thread ends or breakage.

[0033] In the thread-cutting structure of the sewing machine described above, the surface of the thread tip b to be cut is an arc surface concentric with the drive shaft, and the thread tip b to be cut and the thread-cutting tip c of the tail needle are smoothly connected. Because the surface of the thread tip b to be cut is an arc surface concentric with the drive shaft, the auxiliary knife stops moving and waits to cut the thread as the thread tip b slides past the second abutment. It continues until the moving blade edge moves to below the needle hole on the needle plate, then swings upward to cut the thread on the tail needle and the bottom thread. This allows the auxiliary knife to approach the moving knife in a better posture for cutting the thread, improving the stability and accuracy of thread cutting and avoiding uneven thread breaks or failed thread cutting.

[0034] In the thread-cutting structure of the sewing machine described above, the starting thread-cutting tip a and the thread-to-be-cutting tip b are connected by a connecting concave arc segment ab. This design allows the auxiliary blade cam to slide from the starting thread-cutting tip a across the connecting concave arc segment ab to the thread-to-be-cutting tip b, while the auxiliary blade first swings downwards and then upwards. The downward swing allows the auxiliary blade to avoid the needle, preventing the needle from hitting the auxiliary blade and allowing the needle to perform the second, third, and subsequent sewing actions. The upward swing allows the auxiliary blade to swing upwards to the position where the thread is to be cut.

[0035] In the thread-cutting structure of the sewing machine described above, the tail needle thread-cutting tip c and the starting needle thread-cutting tip a are connected by a connecting convex arc segment ca. Since the distance from each point of the connecting convex arc segment ca to the center of the drive shaft is less than the distance from the tail needle thread-cutting tip c (and the starting needle thread-cutting tip a) to the center of the drive shaft, after the tail needle top thread and bottom thread are cut, as the connecting convex arc segment ca slides past the abutment part two, the auxiliary blade will first swing downward and then upward. This downward swing avoids the needle, allowing the needle to pass downward through the lower needle hole on the moving blade to achieve the first stitch. The upward swing engages with the moving blade edge to cut the starting needle top thread.

[0036] Compared with existing technologies, the thread-cutting structure of this sewing machine has the following advantages:

[0037] 1. In this thread-cutting structure, a thread-cutting arc surface concentric with the drive shaft is also provided on the first convex arc segment BC. The design of this thread-cutting arc surface allows the auxiliary knife cam to rotate and drive the auxiliary knife to move towards the moving knife to cut the thread, while the moving knife remains stationary and waits for the auxiliary knife to approach to cut the thread. Therefore, this thread-cutting method adopts a "one stationary and one moving" approach to cut the thread, which can more accurately control the thread-cutting position below the needle hole of the needle plate, so that the thread-cutting position is closer to the needle hole, thereby shortening the starting thread remaining on the fabric as much as possible, thus achieving a better anti-bird nest effect.

[0038] 2. In this wire-cutting structure, since both the moving blade cam and the auxiliary blade cam are fixedly connected to the drive shaft, a single motor can drive both cams to rotate. This eliminates the potential error accumulation that can occur when using two separate motors, simplifies the control algorithm, and makes the movements of the moving blade and the auxiliary blade more coordinated. Furthermore, because the geometry of the moving blade cam and the auxiliary blade cam is pre-designed and they are driven by the same drive shaft, their respective positions and their engagement relationship depend on the rotation angle of the drive shaft. In other words, when the motor drives the drive shaft to a specific angle, the moving blade and the auxiliary blade will reach the corresponding position and form the corresponding engagement relationship. This design allows the moving blade and the auxiliary blade to perform wire cutting and post-cutting resetting actions more precisely, improving the working stability and reliability of the wire-cutting structure. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the wire shearing structure installed on the machine base.

[0040] Figure 2 This is a schematic diagram of the three-dimensional structure of the shear wire structure.

[0041] Figure 3 This is a schematic diagram of the transmission structure for the moving tool.

[0042] Figure 4 This is a three-dimensional structural diagram of the moving cam.

[0043] Figure 5 This is a schematic diagram of the corresponding part of the working circumferential surface on the moving cam.

[0044] Figure 6 This is a schematic diagram of the auxiliary tool cam.

[0045] Figure 7 This is a front view of the shear wire structure in its initial state.

[0046] Figure 8 This is a partial schematic diagram of the shear wire structure in its initial state.

[0047] Figure 9This is a schematic diagram showing the motion relationship between the moving cam and the auxiliary cam when the wire shearing structure is in its initial state.

[0048] Figure 10 This is a front view of the sheared wire structure when it is in the pressing state.

[0049] Figure 11 This is a schematic diagram showing the motion relationship between the moving cam and the auxiliary cam when the wire shearing structure is in the wire pressing state.

[0050] Figure 12 This is a front view of the process of cutting the starting thread of this thread-cutting structure.

[0051] Figure 13 This is a partial schematic diagram of the process of cutting the starting thread of this thread-cutting structure.

[0052] Figure 14 This is a schematic diagram showing the motion relationship between the moving cam and the auxiliary cam during the process of cutting the starting thread of this thread-cutting structure.

[0053] Figure 15 This is a front view of the process of hooking the wire in this wire-cutting structure.

[0054] Figure 16 This is a partial schematic diagram of the hooking process of this wire-cutting structure.

[0055] Figure 17 This is a schematic diagram showing the motion relationship between the moving cam and the auxiliary cam during the hooking process of this wire-cutting structure.

[0056] Figure 18 This is a front view of the process of cutting the top and bottom threads of the tail needle in this thread-cutting structure.

[0057] Figure 19 This is a partial schematic diagram of the process by which the shearing structure cuts the top and bottom threads of the tail needle.

[0058] Figure 20 This is a schematic diagram showing the motion relationship between the moving cam and the auxiliary cam during the process of this wire-cutting structure cutting the top and bottom threads of the tail needle.

[0059] In the diagram: 1. Base; 2. Needle plate; 21. Needle drop hole; 3. Moving knife; 31. Moving knife cutting edge; 32. Lower needle hole; 33. Thread hook groove; 4. Auxiliary knife; 41. Auxiliary knife cutting edge; 5. Drive shaft; 6. Moving knife linkage assembly; 61. First abutment part; 7. Auxiliary knife linkage assembly; 71. Second abutment part; 8. Moving knife cam; 81. Thread cutting arc surface; 9. Auxiliary knife cam; 10. Rotary hook; 11. Thread pressing plate; 12. Servo motor; 13. Knife holder; 14. Lower connecting rod; 15. Upper connecting rod; 16. Hinge shaft; 17. Suction pipe. Detailed Implementation

[0060] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0061] like Figure 1 and Figure 2 As shown, the thread-cutting structure of this sewing machine includes a base 1, a rotary hook 10, and a needle plate 2 with a needle drop hole 21. The thread-cutting structure includes a moving blade cam 8, an auxiliary blade cam 9, a thread pressing plate 11 located beside the rotary hook 10, and a moving blade 3 and an auxiliary blade 4, both positioned below the needle plate 2. The moving blade 3 has a moving blade edge 31, a needle drop hole 32, and a thread hook groove 33 located between the moving blade edge 31 and the needle drop hole 32. The lower edge of the auxiliary blade 4 near the needle end forms an auxiliary blade edge 41. Furthermore, the base 1 also includes a drive shaft 5, a moving blade linkage assembly 6 connected to the moving blade 3, and an auxiliary blade linkage assembly 7 connected to the auxiliary blade 4. The moving blade cam 8 and the auxiliary blade cam 9 are arranged parallel to each other and are both fixedly connected to the drive shaft 5. A servo motor 12, capable of driving the drive shaft 5 to rotate, is fixedly connected to the bottom of the frame.

[0062] like Figure 2 and Figure 3 As shown, both the moving knife linkage assembly 6 and the auxiliary knife linkage assembly 7 include an annular knife holder 13, a lower connecting rod 14, and an upper connecting rod 15. The moving knife 3 and the auxiliary knife 4 are respectively mounted on their respective knife holders 13. The annular knife holder 13 is rotatably mounted on the machine base 1, and its rotation center line coincides with the center line of the sewing machine shuttle 10. In the moving knife linkage assembly 6, one end of the upper connecting rod 15 is hinged to the knife holder 13 corresponding to the moving knife 3, and the other end is hinged to one end of the lower connecting rod 14. The other end of the lower connecting rod 14 is hinged to the machine base 1 through a hinge shaft 16. The middle part of the lower connecting rod 14 of the moving knife linkage assembly 6 has a contacting part 61 that abuts against the working circumferential surface of the moving knife cam 8. When the servo motor 12 drives the drive shaft 5 to rotate, the power is transmitted through the moving blade cam 8 and the moving blade connecting rod assembly 6, which can drive the moving blade 3 to swing up and down around the outer periphery of the rotary shuttle 10. When the working circumferential surface of the moving blade cam 8 pushes against the abutment part 61 and moves away from the axis of the drive shaft 5, the moving blade 3 swings downward, and vice versa.

[0063] like Figure 2As shown, in the auxiliary knife linkage assembly 7, one end of the upper linkage 15 is hinged to the knife holder 13 corresponding to the auxiliary knife 4, and the other end is hinged to one end of the lower linkage 14. The other end of the lower linkage 14 is also hinged to the machine base 1 via the hinge shaft 16. The middle part of the lower linkage 14 of the auxiliary knife linkage assembly 7 has a second abutting part 71 that abuts against the working circumferential surface of the auxiliary knife cam 9. When the drive shaft 5 drives the auxiliary knife cam 9 to rotate, the auxiliary knife 4 can be driven to swing up and down around the outer circumference of the rotary hook 10 above the pressure plate 11 by power transmission through the auxiliary knife cam 9 and the auxiliary knife linkage assembly 7. When the working circumferential surface of the auxiliary knife cam 9 pushes against the second abutting part 71 and moves away from the axis of the drive shaft 5, the auxiliary knife 4 swings upward, and vice versa.

[0064] like Figure 4 and Figure 5 As shown, the working circumferential surface of the moving cam 8 includes a first concave arc segment AB, a first convex arc segment BC, a second concave arc segment CD, and a second convex arc segment DA connected end to end in sequence. Figure 5 From the perspective of the drive shaft 5, the moving cam 8 rotates clockwise in a unidirectional cycle, causing the first concave arc segment AB, the first convex arc segment BC, the second concave arc segment CD, and the second convex arc segment DA to slide sequentially over the abutment part 61. The auxiliary cam 9 and the moving cam 8 rotate synchronously and in the same direction.

[0065] Specifically, such as Figure 5 As shown, the second convex arc segment DA is an arc surface concentric with the drive shaft 5. The length of the second convex arc segment DA is less than the length of the first convex arc segment BC. The first convex arc segment BC has a sheared arc surface 81 concentric with the drive shaft 5. The distances from the starting point B and ending point C of the first convex arc segment BC to the axis of the drive shaft 5 are both greater than the distance from the sheared arc surface 81 to the axis of the drive shaft 5.

[0066] like Figure 6 As shown, the working circumferential surface of the fixed-blade cam has a starting needle cutting tip a, a thread cutting tip b, and a tail needle cutting tip c arranged sequentially along the circumference. The starting needle cutting tip a and the tail needle cutting tip are equidistant from the center of the drive shaft 5, and the distances from the starting needle cutting tip a and the tail needle cutting tip c to the center of the drive shaft 5 are greater than the distances from all other surfaces to the center of the drive shaft 5, and therefore greater than the distance from the thread cutting tip b to the center of the drive shaft 5. The starting needle cutting tip a and the thread cutting tip b are connected by a concave arc segment ab. The surface of the thread cutting tip b is an arc surface concentric with the drive shaft 5. The thread cutting tip b and the tail needle cutting tip c are smoothly connected, and the tail needle cutting tip c and the starting needle cutting tip a are connected by a convex arc segment ca.

[0067] The wire-cutting method of this wire-cutting structure includes the following steps:

[0068] 1. Initial state: such as Figure 7 , Figure 8 and Figure 9 As shown, before the first stitch is inserted, the drive shaft 5 drives the moving cutter cam 8 to rotate to the concave inflection point of the first concave arc segment AB, where it abuts against the first abutment part 61. At this time, the needle hole 32 on the moving cutter 3 is vertically aligned with the needle drop hole 21 on the needle plate 2, while the first half of the connecting convex arc segment ca on the auxiliary cutter cam 9 abuts against the second abutment part 71, making the position of the auxiliary cutter 4 lower than the thread cutting position to avoid the needle's insertion trajectory. The needle first passes downward through the needle hole 32 on the moving cutter 3, then moves upward away from the needle hole 32 and is lifted above the needle plate 2, completing the first stitch insertion action of the needle. The thread on the needle remains within the needle hole 32.

[0069] 2. Pressing lines: such as Figure 10 and Figure 11 As shown, after the first stitch of the needle is inserted and the needle is lifted, the drive shaft 5 continues to drive the moving blade cam 8 to rotate. At this time, the latter half of the first concave arc segment AB pushes the abutment part 61 to move away from the axis of the drive shaft 5, causing the moving blade 3 to swing downward with the starting thread until the starting point B of the first convex arc segment BC abuts against the abutment part 61. At this time, the moving blade 3 swings to the lower stop point, and the lower side of the moving blade 3 abuts against the thread clamping plate 11 to hold the starting thread passing through the lower needle hole 32. During this process, the auxiliary blade 4 also swings downward for a certain distance to prevent it from engaging with the moving blade 3 during the downward swing and prematurely cutting the thread.

[0070] 3. Cut the starting thread: As the needle begins its second stitch, the top thread on the needle locks with the bottom thread in the rotary hook 10 mechanism. After the needle has been sewn to the set number of stitches, such as two, three, or four stitches, the drive shaft 5 drives the moving blade 3 to continue oscillating. Figure 12 , Figure 13 and Figure 14 As shown, during the process of the shearing arc surface 81 on the first convex arc segment BC sliding past the abutment part 61, the moving blade 3 stops at a position where its moving blade edge 31 is directly below the needle drop hole 21. During this process, the needle-starting shearing tip a on the auxiliary blade cam 9 slides past the abutment part 71, causing the auxiliary blade 4 to move towards the moving blade edge 31 and engage with it, thus cutting the starting needle thread. Furthermore, during this process, before cutting the starting needle thread, the suction pipe 17 is already in suction mode and the thread clamping plate 11 has released the starting needle thread, allowing the cut thread end to be directly sucked away by the suction pipe 17.

[0071] 4. Continue sewing: After the starting thread is cut, the drive shaft 5 continues to drive the moving blade cam 8 and the auxiliary blade cam 9 to rotate until the end point C of the first convex arc segment BC abuts against the first abutment part 61. Meanwhile, the auxiliary blade cam 9 slides along the second abutment part 71 from the starting thread cutting tip a to the concave inflection point connecting the concave arc segment ab. During this process, both the moving blade 3 and the auxiliary blade 4 swing downward from the thread cutting position, allowing them to avoid the needle's insertion position. The needle will not collide with the moving blade 3 and the auxiliary blade 4, thus enabling the sewing machine to continue sewing until the last stitch is completed.

[0072] 5. Outlining: such as Figure 15 , Figure 16 and Figure 17 As shown, after the last stitch is completed, the drive shaft 5 rotates the moving knife cam 8 and the auxiliary knife cam 9. As the moving knife cam 8 moves from the end point C of the first convex arc segment BC to the concave inflection point of the second concave arc segment CD, against the abutment part 61, the moving knife 3 swings upwards and, relying on the thread-separating tip at its front end, pushes one of the bottom thread and top thread loops towards the side of the thread-separating tip. As the moving knife 3 continues to swing upwards, the bottom thread and top thread slide along the side wall of the moving knife 3 until the concave inflection point of the second concave arc segment CD abuts against the abutment part 61. At this point, the hook groove 33 on the moving knife 3 aligns vertically with the needle hole 21 on the needle plate 2, allowing the bottom thread and top thread to smoothly enter the hook groove 33. During this process, the auxiliary knife cam 9 slides against the abutment part 71 from the concave inflection point of the connecting concave arc segment ab towards the tip b of the thread to be cut, causing the auxiliary knife 4 to swing upwards to the position of the thread to be cut.

[0073] 6. Cutting the tail needle face and bottom thread: The moving blade cam 8 and the auxiliary blade cam 9 continue to rotate. As the moving blade cam 8 moves from the concave inflection point of the second concave arc segment CD to the starting point D of the second convex arc segment DA, it slides downwards, causing the moving blade edge 31 of the moving blade 3 to move closer to the needle drop hole 21. At the same time, the moving blade edge 31 of the moving blade 3 moves closer to the tail needle face and bottom thread. During this process, the auxiliary blade cam 9 slides along the tip b of the thread to be cut. Since the surface of the tip b of the thread to be cut is a circular arc surface concentric with the drive shaft 5, the auxiliary blade 4 stops and waits to cut the thread as the tip b of the thread to be cut slides past the second abutment part 71.

[0074] As the moving tool cam 8 and the auxiliary tool cam 9 continue to rotate, Figure 18 , Figure 19 and Figure 20As shown, during the process of the second convex arc segment DA on the moving blade cam 8 sliding past the first abutment part 61, the tail needle cutting tip c on the auxiliary blade cam 9 can slide past the second abutment part 71, causing the auxiliary blade 4 to move towards the moving blade edge 31 and engage with the moving blade edge 31 of the moving blade 3, cutting the tail needle top thread and bottom thread. During this process, since the second convex arc segment DA is an arc surface concentric with the drive shaft 5, when the second convex arc segment DA slides past the first abutment part 61, the moving blade 3 will also stop at a position where its moving blade edge 31 is directly below the needle drop hole 21. This makes the thread cutting position closer to the needle drop hole 21, so that after sewing, the cut tail needle top thread and bottom thread are as short as possible, improving the sewing bird's nest effect.

[0075] 7. Reset: The moving tool cam 8 and the auxiliary tool cam 9 continue to rotate, causing the moving tool 3 and the auxiliary tool 4 to reset to their original positions. Figure 7 , Figure 8 and Figure 9 The initial state shown indicates that the machine is waiting for the next sewing session. Of course, during actual sewing, the moving blade 3 and the auxiliary blade 4 can be reset to other positions. When the sewing machine needs to be started for the next sewing session, the control system controls the servo motor 12 to move the moving blade 3 and the auxiliary blade 4 to their respective positions. Figure 7 , Figure 8 and Figure 9 The initial state is shown.

[0076] The specific embodiments described herein are merely illustrative examples illustrating the spirit of this utility model. Those skilled in the art to which this utility model pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of this utility model or exceeding the scope defined by the appended claims.

[0077] Although this document frequently uses terms such as 1. base; 2. needle plate; 21. needle drop hole; 3. moving knife; 31. moving knife cutting edge; 32. lower needle hole; 33. hook groove; 4. auxiliary knife; 41. auxiliary knife cutting edge; 5. drive shaft; 6. moving knife linkage assembly; 61. first abutment; 7. auxiliary knife linkage assembly; 71. second abutment; 8. moving knife cam; 81. thread cutting arc surface; 9. auxiliary knife cam; 10. rotary hook; 11. thread pressing plate; 12. servo motor; 13. knife holder; 14. lower linkage; 15. upper linkage; 16. hinge shaft; 17. suction pipe, etc., the possibility of using other terms is not excluded. The use of these terms is merely for the convenience of describing and explaining the essence of this utility model; interpreting them as any additional limitation would contradict the spirit of this utility model.

Claims

1. A thread trimming structure of a sewing machine, the sewing machine comprising a machine base (1) and a needle plate (2) having a needle drop hole (21), the thread trimming structure comprising an auxiliary cutter (4) and a movable cutter (3) having a movable cutter blade edge (31) which are both arranged below the needle plate (2), a driving shaft (5), a movable cutter link assembly (6) connected to the movable cutter (3) and an auxiliary cutter link assembly (7) connected to the auxiliary cutter (4) are further arranged on the machine base (1), characterized in that, The shearing line structure further comprises a moving knife cam (8) and an auxiliary knife cam (9), which are arranged in parallel and are fixedly connected to the driving shaft (5), and the moving knife connecting rod assembly (6) has a first abutting part (61) abutting against the working peripheral surface of the moving knife cam (8); The working peripheral surface of the moving knife cam (8) comprises a first concave arc segment AB, a first convex arc segment BC, a second concave arc segment CD and a second convex arc segment DA connected in sequence, and the first convex arc segment BC has a shearing line arc surface (81) concentric with the driving shaft (5); When the shearing line arc surface (81) on the moving knife cam (8) slides through the first abutting part (61), the moving knife (3) stops at a position where the moving knife edge (31) is located directly below the needle falling hole (21), and in this process, the auxiliary knife cam (9) can drive the auxiliary knife (4) to move towards the moving knife edge (31) and engage with the moving knife edge (31) through the auxiliary knife connecting rod assembly (7).

2. The thread trimming structure of the sewing machine according to claim 1, characterized by The sewing machine further comprises a rotating hook (10), the moving knife (3) swings up and down around the outer periphery of the rotating hook (10), and when the working peripheral surface of the moving knife cam (8) pushes the first abutting part (61) to move away from the axis of the driving shaft (5), the moving knife (3) swings downward, and the shearing line structure further comprises a thread pressing piece (11) located beside the rotating hook (10), when the starting point B of the first convex arc segment BC abuts against the first abutting part (61), the moving knife (3) swings downward to the lowest point, and the lower side of the moving knife (3) abuts against the thread pressing piece (11).

3. The thread trimming structure of the sewing machine according to claim 2, characterized by, The side of the thread pressing piece (11) is further provided with an air suction pipe (17), and when the moving knife (3) swings upward, the moving knife (3) can be separated from the thread pressing piece (11).

4. The thread trimming structure of the sewing machine according to claim 2 or 3, characterized in that, The auxiliary knife connecting rod assembly (7) has a second abutting part (71) abutting against the working peripheral surface of the auxiliary knife cam (9), the working peripheral surface of the auxiliary knife cam (9) has a needle starting shearing line peach tip a and a needle ending shearing line peach tip c arranged in sequence along the circumference, and the distance from the needle starting shearing line peach tip a and the needle ending shearing line peach tip c to the axis of the driving shaft (5) is greater than the distance from the rest of the surface to the axis of the driving shaft (5); When the shearing line arc surface (81) on the moving knife cam (8) slides through the first abutting part (61), the needle starting shearing line peach tip a on the auxiliary knife cam (9) can slide through the second abutting part (71) to make the auxiliary knife (4) move towards the moving knife edge (31) and engage with the moving knife edge (31); When the second convex arc segment DA on the moving knife cam (8) slides through the first abutting part (61), the needle ending shearing line peach tip c on the auxiliary knife cam (9) can slide through the second abutting part (71) to make the auxiliary knife (4) move towards the moving knife edge (31) and engage with the moving knife edge (31).

5. The thread trimming structure of the sewing machine according to claim 4, wherein The second convex arc segment DA is a circular arc surface concentric with the driving shaft (5), and the distance from the needle starting shearing line peach tip a and the needle ending shearing line peach tip c to the axis of the driving shaft (5) is equal.

6. The thread trimming structure of the sewing machine according to claim 2 or 3, characterized by The moving knife (3) also has a lower needle hole (32), the moving knife edge (31) is located in front of the lower needle hole (32) in the swinging direction of the moving knife (3), the distance from the starting point B and the ending point C of the first convex arc segment BC to the axis of the driving shaft (5) is greater than the distance from the shearing line circular surface (81) to the axis of the driving shaft (5), and the lower needle hole (32) on the moving knife (3) is vertically opposite to the needle falling hole (21) on the needle plate (2) when the inflection point of the first concave arc segment AB abuts against the abutting part one (61).

7. The thread trimming structure of the sewing machine according to claim 6, wherein The moving knife (3) also has a hooking line groove (33) between the moving knife edge (31) and the lower needle hole (32), the hooking line groove (33) on the moving knife (3) is vertically opposite to the needle falling hole (21) on the needle plate (2) when the inflection point of the second concave arc segment CD abuts against the abutting part one (61).

8. The thread trimming structure of the sewing machine according to claim 1 or 2, characterized by The length of the second convex arc segment DA is less than the length of the first convex arc segment BC.

9. The thread trimming structure of the sewing machine according to claim 4, wherein The auxiliary knife (4) swings up and down around the outer periphery of the rotating hook (10) above the pressing line piece (11), and the auxiliary knife (4) swings upward when the working peripheral surface of the auxiliary knife cam (9) pushes the abutting part two (71) to move away from the axis of the driving shaft (5); the working peripheral surface of the auxiliary knife cam (9) also has a to-be-cut line peach tip b, and the starting needle cutting line peach tip a, the to-be-cut line peach tip b and the tail needle cutting line peach tip c are sequentially arranged along the circumference of the auxiliary knife cam (9).

10. The thread trimming structure of the sewing machine according to claim 9, wherein The surface of the to-be-cut line peach tip b is a circular surface concentric with the driving shaft (5), and the to-be-cut line peach tip b and the tail needle cutting line peach tip c are smoothly connected.

Images