A double-cam type sewing machine thread cutting structure

Abstract

The present invention provides a double-cam type sewing machine thread cutting structure, belonging to the technical field of sewing machines. It solves the problem of insufficient anti-bird nest groove effect of the existing thread cutting structure. This thread cutting structure further includes a moving knife cam and an auxiliary knife cam. The moving knife cam and the auxiliary knife cam are arranged in parallel at intervals and are both fixedly connected to the driving shaft. The working peripheral surface of the moving knife 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 that are sequentially connected end to end. There is a thread cutting arc surface concentric with the driving shaft on the first convex arc segment BC; when the thread cutting arc surface on the moving knife cam slides past the first abutting part, the moving knife stops at a position where its moving knife edge is directly below the needle dropping hole, and during this process, the starting needle thread cutting tip a on the auxiliary knife cam can slide past the second abutting part to make the auxiliary knife move towards the moving knife edge direction and engage with the moving knife edge of the moving knife. The present invention has the advantages of stable operation and good anti-bird nest effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewing machines and relates to a thread cutting structure of a double-cam type sewing machine. Background Art

[0002] A sewing machine is a device that uses one or more sewing threads to form one or more stitches on fabric, so as to interweave or sew two or more layers of fabric together. In order to improve sewing efficiency, a thread cutting structure is usually provided on the sewing machine. The thread cutting structure automatically cuts the starting end of the sewing thread of the fabric left on the fabric surface of the starting stitch, otherwise there will be a relatively long thread end, which will form a "bird's nest" phenomenon after knotting, resulting in poor aesthetics. After the last stitch is sewn, it is also necessary to cut the end needle upper thread and the bobbin thread.

[0003] The thread cutting structure of an existing sewing machine, such as the thread cutting method of the thread cutting mechanism of a double-acting knife disclosed in a patent document (application number: 202411329869.0), includes a first thread cutting moving knife and a second thread cutting moving knife. The thread cutting moving knives are respectively installed on a first ring part and a second ring part. The first ring part and the second ring part are rotatably arranged on the sewing machine base, so that the thread cutting moving knives can respectively rotate around the centers of the first ring part and the second ring part. When the first thread cutting moving knife and the second thread cutting moving knife approach each other, the starting end upper thread is cut. In the actual use process of this thread cutting structure, there are the following deficiencies:

[0004] 1. When the starting end upper thread needs to be cut, during the process of the first thread cutting moving knife retracting downward from the second position (the position swinging upward below the sewing needle), it engages with the second thread cutting moving knife to cut the starting end upper thread. The thread cutting position of this thread cutting structure is relatively far from the needle drop hole of the needle plate, so that the cut end of the upper thread is relatively long from the fabric, that is, the starting end upper thread end left on the fabric is relatively long, and the anti-bird's nest effect is poor.

[0005] 2. It is provided with a second transmission rod sleeved outside the first transmission rod, and the first driving member and the second driving member respectively drive the first transmission rod and the second transmission rod to rotate, and then respectively drive the first thread cutting moving knife and the second thread cutting moving knife to swing up and down. That is, this thread cutting structure uses two motors to respectively drive the first thread cutting moving knife and the second thread cutting moving knife to swing. At this time, since the two motors operate independently, the two motors require more complex control algorithms to coordinate the cooperation relationship between the first thread cutting moving knife and the second thread cutting moving knife. This complexity is likely to increase the risk of potential failures, and it is easy to cause a change in the cooperation relationship between the first thread cutting moving knife and the second thread cutting moving knife, thereby affecting the working stability and reliability of thread cutting. Summary of the Invention

[0006] The purpose of the present invention is to address the above problems existing in the prior art and propose a thread cutting structure of a double-cam type sewing machine. The present invention solves the problem of insufficient anti-bird's nest effect of the existing thread cutting structure and improves the working stability of the thread cutting structure.

[0007] The object of the present invention can be achieved by the following technical solutions: A double-cam type sewing machine thread cutting structure. The sewing machine includes a machine base and a needle plate with a needle dropping hole. This thread cutting structure includes a moving knife and an auxiliary knife both arranged below the needle plate. The machine base is further provided with a driving shaft, a moving knife link assembly connected to the moving knife, and an auxiliary knife link assembly connected to the auxiliary knife. It is characterized in that this thread cutting structure further includes a moving knife cam and an auxiliary knife cam. The moving knife cam and the auxiliary knife cam are arranged in parallel at intervals and are both fixedly connected to the driving shaft. The moving knife link assembly has a first abutting portion that abuts against the working peripheral surface of the moving knife cam, and the auxiliary knife link assembly has a second abutting portion that abuts against the working peripheral surface of the auxiliary knife cam;

[0008] The working peripheral surface of the moving knife 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 that are sequentially connected end to end. There is a thread cutting arc surface concentric with the driving shaft on the first convex arc segment BC;

[0009] The working peripheral surface of the auxiliary knife cam has a starting needle thread cutting peach tip a and a tail needle thread cutting peach tip c arranged in sequence along the circumference. The distances from the starting needle thread cutting peach tip a and the tail needle thread cutting peach tip c to the axis of the driving shaft are greater than the distances from the surfaces at other places to the axis of the driving shaft;

[0010] When the thread cutting arc surface on the moving knife cam slides past the first abutting portion, the moving knife stops at a position where its moving knife edge is directly below the needle dropping hole. And during this process, the starting needle thread cutting peach tip a on the auxiliary knife cam can slide past the second abutting portion to make the auxiliary knife move towards the moving knife edge direction and bite with the moving knife edge of the moving knife;

[0011] When the second convex arc segment DA on the moving knife cam slides past the first abutting portion, the tail needle thread cutting peach tip c on the auxiliary knife cam can slide past the second abutting portion to make the auxiliary knife move towards the moving knife edge direction and bite with the moving knife edge of the moving knife.

[0012] In this thread cutting structure, since both the moving knife cam and the auxiliary knife cam are fixedly connected to the driving shaft, a single motor can be used to drive the rotation of the moving knife cam and the auxiliary knife cam. In this way, the error accumulation that may occur between the two motors when two motors are used to drive separately can be eliminated, and the control algorithm can be simplified, making the movements of the moving knife and the auxiliary knife more coordinated and consistent, and improving the working stability and reliability of the thread cutting structure.

[0013] As a further improvement, in the present thread trimming structure, a thread trimming arc surface is also provided on the first convex arc segment BC, which is concentric with the drive shaft. Since the distance from the abutment portion 1 to the drive shaft (or the rotation center of the moving knife cam) does not change during the process of the thread trimming arc surface sliding over the abutment portion 1, the moving knife can remain stationary during the process. Therefore, the design of the thread trimming arc surface enables the auxiliary knife cam to rotate and drive the auxiliary knife to move toward the moving knife to trim the thread. Even if the moving knife cam must rotate with the drive shaft, the moving knife can remain in a stopped state and wait for the auxiliary knife to approach to trim the thread. Compared with the situation where both the moving knife and the auxiliary knife move to engage, the present thread trimming method uses a "static and dynamic" method to trim the thread, which can more accurately control the thread trimming position below the needle plate needle hole, thereby making the thread trimming position closer to the needle hole, thereby shortening the needle thread remaining on the fabric as much as possible, thereby achieving a better anti-bird nest effect.

[0014] Furthermore, since the position of the moving knife is directly controlled by the shape of the moving knife cam, after a thread-cutting arc surface concentric with the drive shaft is provided on the moving knife cam, even if the motor that drives the drive shaft to rotate has a slight error in the rotation angle, it will not affect the final position of the moving knife, thereby ensuring that the moving knife is always located directly below the needle drop hole waiting for thread cutting. Relatively speaking, if a motor is used to directly drive the moving knife to move through a connecting rod, the rotation angle error of the motor will be directly transmitted to the moving knife, so any slight error will cause a change in the position of the moving knife, and therefore it is impossible to ensure that the engagement position of the moving knife and the auxiliary knife is always directly below the needle drop hole. Therefore, the thread cutting method of the present invention can tolerate a certain error in the motor without affecting the precise position of the thread cutting, thereby being able to more accurately control the thread cutting position below the needle drop hole of the needle plate, achieving a better anti-bird nest effect.

[0015] During sewing, the driving shaft drives the movable knife cam to rotate in a clockwise unidirectional cycle, so that 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 slide over the abutment portion 1 in sequence. The auxiliary knife cam and the movable knife cam rotate synchronously and in the same direction. Since the working circumference of the movable knife 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 in sequence, the shape of the working circumference is designed so that when the movable knife cam rotates one circle, it can drive the movable knife to swing up and down twice. Similarly, since the distance from the needle thread cutting peach tip a and the tail needle thread cutting peach tip c on the working circumference of the auxiliary knife cam to the axis of the driving shaft is greater than the distance from the other surfaces to the axis of the driving shaft, when the auxiliary knife cam rotates one circle, it also has two movements of approaching and moving away from the movable knife, so that the driving shaft drives the movable knife cam and the auxiliary knife cam to rotate one circle, so that the needle thread can be cut, and the tail needle thread and the bottom thread can be cut after sewing. Specifically:

[0016] During the process that the thread-cutting arc surface on the moving knife cam slides past the first abutting part, the starting needle thread-cutting cam tip a on the auxiliary knife cam slides past the second abutting part, causing the auxiliary knife to move towards the cutting edge of the moving knife and engage with the cutting edge of the moving knife, thus cutting the starting needle upper thread.

[0017] During the process that the second convex arc segment DA on the moving knife cam slides past the first abutting part, the end needle thread-cutting cam tip c on the auxiliary knife cam slides past the second abutting part, causing the auxiliary knife to move towards the cutting edge of the moving knife and engage with the cutting edge of the moving knife, thus cutting the end needle upper thread and the bobbin thread.

[0018] In the above-mentioned double-cam type sewing machine thread-cutting structure, the second convex arc segment DA is an arc surface concentric with the drive shaft, and the distances from the starting needle thread-cutting cam tip a to the axis of the drive shaft and from the end needle thread-cutting cam tip c to the axis of the drive shaft are equal. This structure enables the auxiliary knife to swing to the same position both when cutting the starting needle thread and when cutting the end needle thread. At the same time, since the second convex arc segment DA is an arc surface concentric with the drive shaft, when the second convex arc segment DA slides past the first abutting part, the moving knife will also stop at a position where its cutting edge is directly below the needle dropping hole, and the auxiliary knife can also move to a position where it engages with the cutting edge of the moving knife. In this way, the thread-cutting position is closer to the needle dropping hole, so that after sewing is completed, the cut end needle upper thread and bobbin thread are as short as possible, improving the sewing nest effect.

[0019] In the above-mentioned double-cam type sewing machine thread-cutting structure, the sewing machine further includes a rotary hook, the moving knife swings up and down around the outer periphery of the rotary hook, and when the working peripheral surface of the moving knife cam pushes the first abutting part to move away from the axis of the drive shaft, the moving knife swings downward. This design utilizes the space outside the rotary hook for the moving knife to swing, not only making the structure compact, but also because the moving knife is always close to the rotary hook, so after the sewing work is completed, it is convenient to accurately cut the bobbin thread on the rotary hook, making the thread-cutting structure work stably and reliably.

[0020] In the above-mentioned double-cam type sewing machine thread-cutting structure, the moving knife has a lower needle hole, along the swinging direction of the moving knife, the cutting edge of the moving knife is located on the front side of the lower needle hole, and the distances from the starting point B and the ending point C of the first convex arc segment BC to the axis of the drive shaft are both greater than the distance from the thread-cutting arc surface to the axis of the drive shaft. When the inner concave inflection point of the first concave arc segment AB abuts against the first abutting part, the lower needle hole on the moving knife is vertically aligned with the needle dropping hole on the needle plate.

[0021] Before the first needle is inserted downward, the drive shaft drives the moving knife cam to rotate until the inner concave inflection point of the first concave arc segment AB abuts against the first abutting part. At this time, the lower needle hole on the moving knife is vertically aligned with the needle dropping hole on the needle plate. The sewing needle first penetrates downward through the lower needle hole, then moves upward away from the lower needle hole and is lifted above the needle plate, completing the first needle insertion action of the sewing needle. The upper thread on the sewing needle remains in the lower needle hole.

[0022] Then, the drive shaft drives the moving knife cam to rotate. At this time, since the first concave arc segment AB will push the abutting part 1 to move away from the axis of the drive shaft, the moving knife drives the needle-threading upper thread to swing downward until the starting point B of the first convex arc segment BC abuts against the abutting part 1. At this time, since the distance from the starting point B to the axis of the drive shaft is greater than the distance from the thread-cutting arc surface to the axis of the drive shaft, the position of the moving knife is lower than the position of the thread to be cut at this time, and the moving knife can avoid the needle-inserting position of the needle, so that the needle-inserting of the needle will not hit the moving knife.

[0023] After that, the needle performs the needle-inserting action of the second needle, and the upper thread on the needle is locked with the bobbin thread in the rotary hook mechanism. After the needle sews the set number of stitches, such as two stitches, three stitches or four stitches, etc. The drive shaft drives the moving knife to continue to swing. When the thread-cutting arc surface on the first convex arc segment BC abuts against the abutting part 1, the moving knife stops at the position where its cutting edge is directly below the needle drop hole. At this time, the auxiliary knife moves towards the cutting edge of the moving knife and engages with the cutting edge of the moving knife, thereby cutting the upper thread.

[0024] After the upper 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 abutting part 1. At this time, since the distance from the end point C to the axis of the drive shaft is also greater than the distance from the thread-cutting arc surface to the axis of the drive shaft, during this process, the moving knife swings downward from the thread-cutting position, so that the moving knife can avoid the needle-inserting position of the needle, so that the needle-inserting of the needle will not hit the moving knife, and then the sewing machine continues to perform subsequent sewing until the last stitch is sewn.

[0025] In the above-mentioned thread-cutting structure of the double-cam sewing machine, the thread-cutting structure further includes a wire pressing piece located beside the rotary hook. When the starting point B of the first convex arc segment BC abuts against the abutting part 1, the lower side surface of the moving knife abuts against the wire pressing piece to clamp the sewing thread passing through the lower needle hole.

[0026] After the first needle-inserting action of the needle is completed and the needle is lifted upward, the moving knife drives the needle-threading upper thread to swing downward until the starting point B of the first convex arc segment BC abuts against the abutting part 1. At this time, the moving knife swings to the lower dead center (i.e., the lowest point), and the lower side surface of the moving knife at this position can abut against the wire pressing piece to clamp the sewing thread passing through the lower needle hole (this sewing thread is the needle-threading upper thread), which can position the needle-threading upper thread, prevent the needle-threading upper thread from flying randomly, facilitate the moving knife and the auxiliary knife to complete the thread-cutting action cleanly, and avoid the situation of thread-cutting failure.

[0027] In the above-mentioned thread-cutting structure of the double-cam sewing machine, the moving knife further has a hook-shaped groove located between the cutting edge of the moving knife and the lower needle hole. When the inner concave inflection point of the second concave arc segment CD abuts against the abutting part 1, the hook-shaped groove on the moving knife is directly opposite to the needle drop hole on the needle plate up and down.

[0028] When the last stitch is sewn, the drive shaft rotates with the moving knife cam. As the moving knife cam moves along the abutting part 1 from the end point C of the first convex arc segment BC to the inner concave inflection point of the second concave arc segment CD, the moving knife will swing upward, and the dividing tip at the front end of the moving knife will deflect one of the tail needle upper threads in the bobbin thread and the upper thread loop to one side of the dividing tip. During the continuous upward swing of the moving knife, the tail needle upper thread and the bobbin thread will slide along the side wall of the moving knife until the inner concave inflection point of the second concave arc segment CD abuts against the abutting part 1, at which time the hook thread groove on the moving knife is directly aligned with the needle drop hole on the needle plate, and the tail needle upper thread and the bobbin thread can smoothly enter the hook thread groove. After that, as the moving knife cam continues to rotate, when the moving knife cam moves along the abutting part 1 from the inner concave inflection point of the second concave arc segment CD to the starting point D of the second convex arc segment DA, the moving knife will swing downward, so that the cutting edge of the moving knife approaches below the needle drop hole, and at the same time, the cutting edge of the moving knife approaches the tail needle upper thread and the bobbin thread, facilitating the auxiliary knife to approach and cut the tail needle upper thread and the bobbin thread.

[0029] In the above-mentioned double-cam type sewing machine thread cutting structure, the length of the second convex arc segment DA is less than the length of the first convex arc segment BC. Since the moving knife remains stationary during the process of the second convex arc segment DA sliding past the abutting part 1, the function of setting the second convex arc segment DA is only to cut the tail needle upper thread and the bobbin thread. At this time, the length of the second convex arc segment DA is shorter than the length of the first convex arc segment BC, which can enable the sewing work to end. After the tail needle upper thread and the bobbin thread are cut, the moving knife can quickly return to the initial state and wait for the next sewing work, thus improving the thread cutting efficiency and the working efficiency of the sewing machine.

[0030] In the above-mentioned double-cam type sewing machine thread cutting structure, the auxiliary knife swings up and down around the outer circumference of the rotary hook, and when the working surface of the auxiliary knife cam pushes the abutting part 2 to move away from the axis of the drive shaft, the auxiliary knife swings upward; the working surface of the auxiliary knife cam also has a thread-to-be-cut peach tip b, and the starting needle thread-cutting peach tip a, the thread-to-be-cut peach tip b, and the tail needle thread-cutting peach tip c are arranged in sequence along the working surface of the auxiliary knife cam.

[0031] Since when the second convex arc segment DA on the moving knife cam slides past the abutting part 1, the tail needle thread-cutting peach tip c on the auxiliary knife cam can slide past the abutting part 2 to move the auxiliary knife towards the cutting edge of the moving knife and engage with the cutting edge of the moving knife to cut the tail needle upper thread and the bobbin thread. Therefore, before cutting the tail needle upper thread and the bobbin thread, the thread-to-be-cut peach tip b will slide past the abutting part 2, enabling the auxiliary knife to move closer to the thread cutting position in advance, rather than approaching the moving knife from a far position instantaneously for thread cutting. Such a design can improve the thread cutting stability of the auxiliary knife, improve the thread cutting effect, and avoid phenomena such as thread pulling or uneven breakage.

[0032] In the above-mentioned double cam sewing machine thread trimming structure, the surface of the thread trimming peach tip b is a circular arc surface concentric with the driving shaft, and the thread trimming peach tip b is smoothly transitionally connected with the tail needle thread trimming peach tip c. Since the surface of the thread trimming peach tip b is a circular arc surface concentric with the driving shaft, the auxiliary knife stops and waits for thread trimming when the thread trimming peach tip b slides over the abutment part 2, until the moving knife edge of the moving knife moves to the bottom of the needle drop hole on the needle plate, and then swings upward to cut the tail needle upper thread and the lower thread, so that the auxiliary knife can approach the moving knife in a better posture to trim the thread, improve the stability and accuracy of thread trimming, and avoid the phenomenon of uneven thread breakage or thread trimming failure.

[0033] In the above-mentioned double cam sewing machine thread trimming structure, the needle thread trimming peach tip a and the to-be-trimmed peach tip b are connected by a connecting concave arc segment ab. This design enables the auxiliary knife cam to slide from the needle thread trimming peach tip a to the to-be-trimmed peach tip b against the abutment portion 2, and the auxiliary knife will first swing downward and then swing upward. By swinging downward, the auxiliary knife avoids the machine needle, so that the machine needle does not hit the auxiliary knife, so that the machine needle can perform the second stitch, the third stitch, etc. sewing action; by swinging upward, the auxiliary knife swings upward to the to-be-trimmed position.

[0034] In the above-mentioned double cam sewing machine thread trimming structure, the tail needle thread trimming peach c is connected to the starting needle thread trimming peach a by the connecting convex arc segment ca. Since the distances from each point of the connecting convex arc segment ca to the axis of the drive shaft are smaller than the distances from the tail needle thread trimming peach c (and the starting needle thread trimming peach a) to the axis of the drive shaft, after the tail needle upper thread and the lower thread are cut, the auxiliary knife will first swing downward and then swing upward in the process of the connecting convex arc segment ca sliding over the abutment portion 2, and the machine needle can be avoided by the downward swing so that the machine needle can pass downward through the lower needle hole on the moving knife to achieve the first stitch sewing, and the upper thread of the starting needle is cut by the upward swing to engage with the moving knife edge of the moving knife.

[0035] Compared with the prior art, the double cam sewing machine thread trimming structure has the following advantages:

[0036] 1. In this thread trimming structure, a thread trimming arc surface concentric with the drive shaft is provided on the first convex arc segment BC. The design of the thread trimming arc surface enables the auxiliary knife cam to rotate and drive the auxiliary knife to move toward the movable knife to trim the thread. The movable knife can remain in a stopped state and wait for the auxiliary knife to approach to trim the thread. Therefore, this thread trimming method adopts a "one static and one dynamic" method to trim the thread, which can more accurately control the thread trimming position below the needle drop hole of the needle plate, so that the thread trimming position is closer to the needle drop hole, thereby shortening the needle thread remaining on the fabric as much as possible, thereby achieving a better anti-bird nest effect.

[0037] 2. In this thread cutting structure, since both the moving knife cam and the auxiliary knife cam are fixedly connected to the drive shaft, a single motor can be used to drive the rotation of both the moving knife cam and the auxiliary knife cam. This eliminates the possible error accumulation between the two motors when two separate motors are used for driving, simplifies the control algorithm, and makes the movements of the moving knife and the auxiliary knife more coordinated. Moreover, since the geometric shapes of the moving knife cam and the auxiliary knife cam are pre-designed and they are driven by the same drive shaft, the respective positions of the moving knife and the auxiliary knife and their cooperation relationship depend on the rotation angle of the drive shaft. That is to say, when the motor drives the drive shaft to rotate to a specific angle, the moving knife and the auxiliary knife will reach their corresponding positions and form a corresponding cooperation relationship. This design enables the moving knife and the auxiliary knife to perform thread cutting and post-cutting reset actions more precisely, improving the working stability and reliability of the thread cutting structure. Brief Description of the Drawings

[0038] Figure 1 is a schematic structural view of this thread cutting structure installed on the machine base.

[0039] Figure 2 is a schematic three-dimensional structural view of this thread cutting structure.

[0040] Figure 3 is a schematic transmission structure view of the moving knife.

[0041] Figure 4 is a schematic three-dimensional structural view of the moving knife cam.

[0042] Figure 5 is a schematic view of the corresponding part of the working surface of the moving knife cam.

[0043] Figure 6 is a schematic view of the auxiliary knife cam.

[0044] Figure 7 is a front view of this thread cutting structure in the initial state.

[0045] Figure 8 is a partial schematic view of this thread cutting structure in the initial state.

[0046] Figure 9 is a schematic view of the movement relationship between the moving knife cam and the auxiliary knife cam of this thread cutting structure in the initial state.

[0047] Figure 10 is a front view of this thread cutting structure in the wire pressing state.

[0048] Figure 11 is a schematic view of the movement relationship between the moving knife cam and the auxiliary knife cam of this thread cutting structure in the wire pressing state.

[0049] Figure 12It is the front view of the process of the thread cutting structure cutting the starting needle upper thread.

[0050] Figure 13 It is a partial schematic diagram of the process of the thread cutting structure cutting the starting needle upper thread.

[0051] Figure 14 It is a schematic diagram of the motion relationship between the moving knife cam and the auxiliary knife cam during the process of the thread cutting structure cutting the starting needle upper thread.

[0052] Figure 15 It is the front view of the process of the thread hooking state of the thread cutting structure.

[0053] Figure 16 It is a partial schematic diagram of the process of the thread hooking state of the thread cutting structure.

[0054] Figure 17 It is a schematic diagram of the motion relationship between the moving knife cam and the auxiliary knife cam during the process of the thread hooking state of the thread cutting structure.

[0055] Figure 18 It is the front view of the process of the thread cutting structure cutting the end needle upper thread and the bobbin thread.

[0056] Figure 19 It is a partial schematic diagram of the process of the thread cutting structure cutting the end needle upper thread and the bobbin thread.

[0057] Figure 20 It is a schematic diagram of the motion relationship between the moving knife cam and the auxiliary knife cam during the process of the thread cutting structure cutting the end needle upper thread and the bobbin thread.

[0058] In the figure, 1. Machine base; 2. Needle plate; 21. Needle dropping hole; 3. Moving knife; 31. Moving knife edge; 32. Lower needle hole; 33. Thread hooking groove; 4. Auxiliary knife; 41. Auxiliary knife edge; 5. Driving shaft; 6. Moving knife connecting rod assembly; 61. First abutting part; 7. Auxiliary knife connecting rod assembly; 71. Second abutting part; 8. Moving knife cam; 81. Thread cutting arc surface; 9. Auxiliary knife cam; 10. Rotating shuttle; 11. Pressing piece; 12. Servo motor; 13. Tool rest; 14. Lower connecting rod; 15. Upper connecting rod; 16. Hinge shaft; 17. Suction air duct. Detailed implementation manners

[0059] The following are specific embodiments of the present invention and in combination with the attached drawings, the technical solutions of the present invention are further described, but the present invention is not limited to this embodiment.

[0060] As Figure 1 and Figure 2As shown in the figure, in the thread trimming structure of this double-cam sewing machine, the sewing machine includes a machine base 1, a rotary hook 10, and a needle plate 2 with a needle dropping hole 21. This thread trimming structure includes a moving knife cam 8, an auxiliary knife cam 9, a presser piece 11 located beside the rotary hook 10, and a moving knife 3 and an auxiliary knife 4 both arranged below the needle plate 2. The moving knife 3 has a moving knife edge 31, a lower needle hole 32, and a thread hooking groove 33 located between the moving knife edge 31 and the lower needle hole 32. The lower edge of the end face of the auxiliary knife 4 near the sewing needle forms an auxiliary knife edge 41. Further, a driving shaft 5, a moving knife link assembly 6 connected to the moving knife 3, and an auxiliary knife link assembly 7 connected to the auxiliary knife 4 are also provided on the machine base 1. The moving knife cam 8 and the auxiliary knife cam 9 are arranged in parallel at intervals and are both fixedly connected to the driving shaft 5. A servo motor 12 capable of driving the driving shaft 5 to rotate is fixedly connected to the bottom of the machine frame.

[0061] As Figure 2 and Figure 3 shown, both the moving knife link assembly 6 and the auxiliary knife link 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 installed on the corresponding knife holders 13. The annular knife holder 13 is rotatably arranged on the machine base 1, and the rotation center line coincides with the center line of the rotary hook 10 of the sewing machine. In the moving knife link assembly 6, one end of its 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 link assembly 6 has a first abutting portion 61 that abuts against the working peripheral surface of the moving knife cam 8. When the servo motor 12 drives the driving shaft 5 to rotate, relying on the power transmission of the moving knife cam 8 and the moving knife link assembly 6, the moving knife 3 can be driven to swing up and down around the outer periphery of the rotary hook 10. When the working peripheral surface of the moving knife cam 8 pushes the first abutting portion 61 to move in a direction away from the axis of the driving shaft 5, the moving knife 3 swings downward, and vice versa, it swings upward.

[0062] As Figure 2 shown, in the auxiliary knife link assembly 7, one end of its upper connecting rod 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 connecting rod 14. The other end of the lower connecting rod 14 is also hinged to the machine base 1 through a hinge shaft 16. The middle part of the lower connecting rod 14 of the auxiliary knife link assembly 7 has a second abutting portion 71 that abuts against the working peripheral surface of the auxiliary knife cam 9. When the driving shaft 5 drives the auxiliary knife cam 9 to rotate, relying on the power transmission of the auxiliary knife cam 9 and the auxiliary knife link assembly 7, the auxiliary knife 4 can be driven to swing up and down around the outer periphery of the rotary hook 10 above the presser piece 11. When the working peripheral surface of the auxiliary knife cam 9 pushes the second abutting portion 71 to move in a direction away from the axis of the driving shaft 5, the auxiliary knife 4 swings upward, and vice versa, it swings downward.

[0063] As Figure 4 and Figure 5As shown, the working peripheral surface of the moving knife 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 that are sequentially connected end to end. At Figure 5 From the perspective of Figure 5 , the drive shaft 5 drives the moving knife cam 8 to rotate clockwise in a one-way cycle, so that 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 sequentially slide past the first abutting portion 61. The auxiliary knife cam 9 rotates synchronously and in the same direction as the moving knife cam 8.

[0064] Specifically, as Figure 5 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. There is a thread-cutting arc surface 81 concentric with the drive shaft 5 on the first convex arc segment BC. The distances from the starting point B and the 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 thread-cutting arc surface 81 to the axis of the drive shaft 5.

[0065] As Figure 6 shown, the working peripheral surface of the auxiliary knife cam 9 has a starting needle thread-cutting peach tip a, a to-be-thread-cut peach tip b, and a tail needle thread-cutting peach tip c arranged sequentially along the circumferential direction. The distances from the starting needle thread-cutting peach tip a to the axis of the drive shaft 5 and from the tail needle thread-cutting peach tip c to the axis of the drive shaft 5 are equal, and the distances from the starting needle thread-cutting peach tip a and the tail needle thread-cutting peach tip c to the axis of the drive shaft 5 are greater than the distances from the surfaces at other positions except these two to the axis of the drive shaft 5. Of course, they are also greater than the distance from the to-be-thread-cut peach tip b to the axis of the drive shaft 5. The starting needle thread-cutting peach tip a and the to-be-thread-cut peach tip b are connected by a connecting concave arc segment ab. The surface of the to-be-thread-cut peach tip b is an arc surface concentric with the drive shaft 5. The to-be-thread-cut peach tip b and the tail needle thread-cutting peach tip c are smoothly connected in a transitional manner. The tail needle thread-cutting peach tip c and the starting needle thread-cutting peach tip a are connected by a connecting convex arc segment ca.

[0066] The thread-cutting method of this thread-cutting structure includes the following steps:

[0067] 1. Initial state: As Figure 7 , Figure 8 and Figure 9 shown, before the first needle is inserted downward, the drive shaft 5 drives the moving knife cam 8 to rotate to the inner concave inflection point of the first concave arc segment AB to abut against the first abutting portion 61. At this time, the needle insertion hole 32 on the moving knife 3 is directly opposite to the needle dropping hole 21 on the needle plate 2 up and down. The first half of the connecting convex arc segment ca on the auxiliary knife cam 9 abuts against the second abutting portion 71, so that the position of the auxiliary knife 4 is lower than the thread-cutting position at this time to avoid the needle insertion trajectory of the sewing needle. The sewing needle first passes downward through the needle insertion hole 32 on the moving knife 3, then leaves the needle insertion hole 32 upward and rises above the needle plate 2, completing the first needle insertion action of the sewing needle. The thread on the sewing needle remains in the needle insertion hole 32.

[0068] 2. Pressing the thread: As Figure 10 andFigure 11 As shown, after the first downward needle insertion action of the sewing needle is completed and the sewing needle is lifted upward, the drive shaft 5 continues to drive the moving knife cam 8 to rotate. At this time, the latter half of the first concave arc segment AB will push against the abutting portion 61 to move in a direction away from the axis of the drive shaft 5, causing the moving knife 3 to swing downward with the starting surface thread, until the starting point B of the first convex arc segment BC abuts against the abutting portion 61. At this time, the moving knife 3 swings to the lower dead point, and the lower side surface of the moving knife 3 abuts against the wire pressing piece 11 to clamp the starting surface thread passing through the lower needle hole 32. During this process, the auxiliary knife 4 will also swing downward for a certain stroke to prevent the moving knife 3 from biting and cutting the surface thread in advance during the downward swing of the moving knife 3.

[0069] 3. Cut the starting surface thread: The sewing needle performs the downward needle insertion action of the second needle, and the surface thread on the sewing needle is locked with the bottom thread in the rotary hook 10 mechanism. After the sewing needle sews the set number of stitches, such as two stitches, three stitches or four stitches, etc. The drive shaft 5 drives the moving knife 3 to continue to swing, as Figure 12 、 Figure 13 and Figure 14 shown, when the thread cutting arc surface 81 on the first convex arc segment BC slides past the abutting portion 61, the moving knife 3 stops at a position where its moving knife edge 31 is directly below the needle dropping hole 21. And during this process, the starting thread cutting peach tip a on the auxiliary knife cam 9 can slide past the abutting portion 71 to make the auxiliary knife 4 move towards the moving knife edge 31 of the moving knife 3 and bite with the moving knife edge 31 of the moving knife 3 to cut the starting surface thread. In addition, during this process, before cutting the starting surface thread, the suction air pipe 17 is already in the suction state and the wire pressing piece 11 has released the starting surface thread, so that the cut surface thread end is directly sucked away by the suction air pipe 17.

[0070] 4. Continue sewing: After the starting surface thread is cut, the drive shaft 5 continues to drive the moving knife cam 8 and the auxiliary knife cam 9 to rotate until the end point C of the first convex arc segment BC abuts against the abutting portion 61, and the auxiliary knife cam 9 slides from the starting thread cutting peach tip a to the inner concave inflection point of the connecting concave arc segment ab along the abutting portion 71. During this process, both the moving knife 3 and the auxiliary knife 4 swing downward from the thread cutting position, so that the moving knife 3 and the auxiliary knife 4 can avoid the downward needle insertion position of the sewing needle, and the downward needle insertion of the sewing needle will not hit the moving knife 3 and the auxiliary knife 4, so that the sewing machine can continue the subsequent sewing until the last stitch is sewn.

[0071] 5. Hook the thread: As Figure 15 、 Figure 16 and Figure 17As shown, when the last stitch is completed, the drive shaft 5 rotates, driving the moving knife cam 8 and the auxiliary knife cam 9. During the process that the moving knife cam 8 abuts against the first abutting portion 61 and moves from the end point C of the first convex arc segment BC to the inflection point of the concave part of the second concave arc segment CD, the moving knife 3 will swing upward, and rely on the thread separating tip at the front end of the moving knife 3 to deflect one of the end needles of the bobbin thread and the loop formed by the needle thread to one side of the thread separating tip. During the process that the moving knife 3 continues to swing upward, the end needle of the needle thread and the bobbin thread will slide along the side wall of the moving knife 3 until when the inflection point of the concave part of the second concave arc segment CD abuts against the first abutting portion 61, the thread hook groove 33 on the moving knife 3 is directly opposite to the needle dropping hole 21 on the needle plate 2 vertically. At this time, the end needle of the needle thread and the bobbin thread can smoothly enter the thread hook groove 33. During this process, the auxiliary knife cam 9 abuts against the second abutting portion 71 and slides from the inflection point of the concave part of the connecting concave arc segment ab towards the starting point b of the peach tip for waiting to cut the thread, causing the auxiliary knife 4 to swing upward to the position for waiting to cut the thread.

[0072] 6. Cutting the end needle of the needle thread and the bobbin thread: The moving knife cam 8 and the auxiliary knife cam 9 continue to rotate. During the process that the moving knife cam 8 abuts against the first abutting portion 61 and moves from the inflection point of the concave part of the second concave arc segment CD to the starting point D of the second convex arc segment DA, the moving knife 3 will swing downward, so that the cutting edge 31 of the moving knife 3 approaches below the needle dropping hole 21, and at the same time, the cutting edge 31 of the moving knife 3 also approaches the end needle of the needle thread and the bobbin thread. During this process, the auxiliary knife cam 9 slides along the peach tip b for waiting to cut the thread. Since the surface of the peach tip b for waiting to cut the thread is a circular arc surface concentric with the drive shaft 5, the auxiliary knife 4 stops moving and waits to cut the thread during the process that the peach tip b for waiting to cut the thread slides past the second abutting portion 71.

[0073] As the moving knife cam 8 and the auxiliary knife cam 9 continue to rotate, as Figure 18 、 Figure 19 and Figure 20 shown, during the process that the second convex arc segment DA on the moving knife cam 8 slides past the first abutting portion 61, the end needle cutting peach tip c on the auxiliary knife cam 9 can slide past the second abutting portion 71, causing the auxiliary knife 4 to move towards the cutting edge 31 of the moving knife 3 and engage with the cutting edge 31 of the moving knife 3, cutting the end needle of the needle thread and the bobbin 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 abutting portion 61, the moving knife 3 will also stop at the position where its cutting edge 31 is directly below the needle dropping hole 21. In this way, the cutting position is closer to the needle dropping hole 21, so that after sewing is completed, the cut end needle of the needle thread and the bobbin thread are as short as possible, improving the sewing nest effect.

[0074] 7. Resetting: The moving knife cam 8 and the auxiliary knife cam 9 continue to rotate, causing the moving knife 3 and the auxiliary knife 4 to reset to the state as shown in Figure 7 、 Figure 8 and Figure 9The initial state shown, waiting for the next sewing. Of course, during the actual sewing process, the moving knife 3 and the auxiliary knife 4 can be reset to other positions. When starting the sewing machine for the next sewing, the control system controls the servo motor 12 to act, so that the moving knife 3 and the auxiliary knife 4 first swing to the initial state as shown in Figure 7 , Figure 8 and Figure 9 .

[0075] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways to replace them, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

[0076] Although terms such as 1, machine base; 2, needle plate; 21, needle dropping hole; 3, moving knife; 31, cutting edge of moving knife; 32, lower needle hole; 33, thread hooking groove; 4, auxiliary knife; 41, cutting edge of auxiliary knife; 5, drive shaft; 6, moving knife link assembly; 61, first abutting part; 7, auxiliary knife link assembly; 71, second abutting part; 8, moving knife cam; 81, thread cutting arc surface; 9, auxiliary knife cam; 10, rotary hook; 11, presser; 12, servo motor; 13, tool holder; 14, lower link; 15, upper link; 16, hinge shaft; 17, air suction pipe are used more in this article, the possibility of using other terms is not excluded. Using these terms is only for more convenient description and explanation of the essence of the present invention; interpreting them as any additional limitation is contrary to the spirit of the present invention.

Claims

1. A double-cam sewing machine thread trimming structure, the sewing machine comprising a machine base (1) and a needle plate (2) having a needle drop hole (21), the thread trimming structure comprising a movable knife (3) and an auxiliary knife (4) both arranged below the needle plate (2), the machine base (1) further comprising a driving shaft (5), a movable knife connecting rod assembly (6) connected to the movable knife (3), and an auxiliary knife connecting rod assembly (7) connected to the auxiliary knife (4), characterized in that: The thread trimming structure further comprises a moving knife cam (8) and an auxiliary knife cam (9), wherein the moving knife cam (8) and the auxiliary knife cam (9) are arranged in parallel and spaced apart and are both fixedly connected to the driving shaft (5), the moving knife connecting rod assembly (6) comprises a first abutting portion (61) abutting against a working circumferential surface of the moving knife cam (8), and the auxiliary knife connecting rod assembly (7) comprises a second abutting portion (71) abutting against a working circumferential surface of the auxiliary knife cam (9); The working circumference of the movable 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 which are connected end to end in sequence, the first convex arc segment BC having a trimming arc surface (81) which is concentric with the drive shaft (5), and the distances from the starting point B and the end 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 trimming arc surface (81) to the axis of the drive shaft (5); The working circumferential surface of the auxiliary knife cam (9) has a needle thread trimming peach tip a and a tail needle thread trimming peach tip c arranged in sequence along the circumferential direction, and the distances from the needle thread trimming peach tip a and the tail needle thread trimming peach tip c to the axis of the drive shaft (5) are greater than the distances from the other surfaces to the axis of the drive shaft (5); When the thread trimming arc surface (81) on the movable knife cam (8) slides over the abutment portion 1 (61), the movable knife (3) stops at a position where the movable knife edge (31) is located directly below the needle drop hole (21), and during this process, the needle thread trimming peach tip a on the auxiliary knife cam (9) can slide over the abutment portion 2 (71) so that the auxiliary knife (4) moves toward the movable knife edge (31) and engages with the movable knife edge (31) of the movable knife (3); When the second convex arc segment DA on the movable knife cam (8) slides over the abutment portion 1 (61), the tail needle thread trimming peach tip c on the auxiliary knife cam (9) can slide over the abutment portion 2 (71), causing the auxiliary knife (4) to move toward the movable knife edge (31) and engage with the movable knife edge (31) of the movable knife (3).

2. The double cam sewing machine thread trimming structure according to claim 1, characterized in that: The second convex arc segment DA is an arc surface concentric with the drive shaft (5), and the distance from the starting needle thread trimming peach tip a to the axis of the drive shaft (5) is equal to the distance from the tail needle thread trimming peach tip c to the axis of the drive shaft (5).

3. The double cam sewing machine thread trimming structure according to claim 1 or 2, characterized in that: The sewing machine further comprises a rotary shuttle (10), the movable knife (3) swings up and down around the outer circumference of the rotary shuttle (10), and the movable knife (3) swings downward when the working circumferential surface of the movable knife cam (8) pushes against abutment portion (61) in a direction away from the axis of the drive shaft (5).

4. The double cam sewing machine thread trimming structure according to claim 3, characterized in that: The movable knife (3) has a lower needle hole (32), and the movable knife edge (31) is located in front of the lower needle hole (32) along the swinging direction of the movable knife (3). When the inner concave turning point of the first concave arc segment AB abuts against the abutment portion 1 (61), the lower needle hole (32) on the movable knife (3) and the needle drop hole (21) on the needle plate (2) are vertically aligned.

5. The double cam sewing machine thread trimming structure according to claim 4, characterized in that: The movable knife (3) further comprises a thread hooking groove (33) located between the movable knife edge (31) and the lower needle hole (32); when the inner concave turning point of the second concave arc segment CD abuts against the abutment portion 1 (61), the thread hooking groove (33) on the movable knife (3) and the needle drop hole (21) on the needle plate (2) are vertically aligned.

6. The double cam sewing machine thread trimming structure according to claim 1 or 2, characterized in that: The length of the second convex arc segment DA is smaller than the length of the first convex arc segment BC.

7. The thread trimming structure of a double cam sewing machine according to claim 3, characterized in that: The auxiliary knife (4) swings up and down around the outer circumference of the rotary hook (10), and when the working circumferential surface of the auxiliary knife cam (9) pushes the second abutment portion (71) to move in a direction away from the axis of the drive shaft (5), the auxiliary knife (4) swings upward; the working circumferential surface of the auxiliary knife cam (9) also has a thread cutting peach tip b, and the starting needle thread cutting peach tip a, the thread cutting peach tip b and the tail needle thread cutting peach tip c are arranged in sequence along the circumference of the auxiliary knife cam (9).

8. The double cam sewing machine thread trimming structure according to claim 7, characterized in that: The surface of the to-be-trimmed peach tip b is an arc surface concentric with the drive shaft (5), and the to-be-trimmed peach tip b is smoothly transitionally connected to the tail needle thread trimming peach tip c.

9. The thread trimming structure of a double cam sewing machine according to claim 7, characterized in that: The needle starting and thread trimming peach tip a and the thread trimming peach tip b are connected by a connecting concave arc segment ab.

10. The double cam sewing machine thread trimming structure according to claim 1 or 2, characterized in that: The tail needle thread trimming peach tip c is connected with the starting needle thread trimming peach tip a through a connecting convex arc segment ca.

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