Trimming structure of double-cam type sewing machine

Abstract

The invention provides a thread trimming structure of a double-cam type 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 further comprises a movable cutter cam and an auxiliary cutter cam, the movable cutter cam and the auxiliary cutter cam are arranged in parallel in a spaced mode and fixedly connected to the driving shaft, and the working circumferential face of the movable 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. The first convex arc section BC is provided with a section of trimming arc surface concentric with the driving shaft; when the thread trimming arc surface on the movable cutter cam slides over the abutting part I, the movable cutter stops at the position where the cutting edge of the movable cutter is located under the needle falling hole; and in the process, a needle raising and thread trimming peach tip a on the auxiliary knife cam can slide over the abutting part II, so that the auxiliary knife moves towards the edge of the movable knife and is engaged with the edge of the movable knife. The device has the advantages of being stable in work and good in bird nest prevention effect.

Description

Technical Field

[0001] The invention belongs to the technical field of sewing machines and relates to a thread trimming structure of a double-cam 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 the fabric, so that two or more layers of fabric are interwoven or sewn together. In order to improve sewing efficiency, a thread cutting mechanism is usually provided on the sewing machine, which automatically cuts off the needle thread remaining on the fabric at the beginning of the sewing stitch. Otherwise, there will be long thread ends, which will form a "bird's nest" phenomenon after clumping and look poor. After the last stitch is sewn, the tail needle thread and the bottom thread also need to be cut off.

[0003] The existing thread trimming structure of the sewing machine, such as the thread trimming method of the patented double-moving knife thread trimming mechanism disclosed in the patent document (application number: 202411329869.0), includes a thread trimming moving knife 1 and a thread trimming moving knife 2, which are respectively mounted on a first ring portion and a second ring portion, and the first ring portion and the second ring portion are rotatably arranged on the sewing machine base, so that the thread trimming moving knife and the thread trimming moving knife can rotate around the center of the first ring portion and the second ring portion respectively, and the needle thread is cut when the thread trimming moving knife 1 and the thread trimming moving knife 2 are close to each other. The thread trimming structure has the following shortcomings in actual use: 1. When the needle thread needs to be cut, the first thread cutting knife moves downward from the second position (swings upward to the position below the needle) and engages with the second thread cutting knife to cut the needle thread. The thread cutting position of the thread cutting structure is far from the needle drop hole of the needle plate, so that the end of the needle thread that is cut is far away from the fabric, that is, the needle thread ends left on the fabric are long, and the anti-bird nest effect is poor.

[0004] 2. It adopts a method of sleeve-mounting a transmission rod 2 on the outside of a transmission rod 1, and drives the transmission rod 1 and the transmission rod 2 to rotate through the first driving member and the second driving member, respectively, and then drives the thread cutting movable knife 1 and the thread cutting movable knife 2 to swing up and down, that is, the thread cutting structure adopts two motors to drive the thread cutting movable knife 1 and the thread cutting movable knife 2 to swing. At this time, since the two motors operate independently, the two motors need a more complex control algorithm to coordinate the matching relationship between the thread cutting movable knife 1 and the thread cutting movable knife 2. This complexity is likely to increase the risk of potential failures, and easily cause the matching relationship between the thread cutting movable knife 1 and the thread cutting movable knife 2 to change, thereby affecting the working stability and reliability of the thread cutting. Summary of the invention

[0005] The purpose of the present invention is to address the above-mentioned problems in the existing technology and propose a double-cam sewing machine thread trimming structure. The present invention solves the problem that the bird-proof groove of the existing thread trimming structure is insufficient and improves the working stability of the thread trimming structure.

[0006] The object of the present invention can be achieved through the following technical solutions: a double-cam sewing machine thread trimming structure, the sewing machine includes a machine base and a needle plate with a needle drop hole, the thread trimming structure includes a moving knife and an auxiliary knife both arranged below the needle plate, the machine base is also provided with a driving shaft, a moving knife connecting rod assembly connected to the moving knife, and an auxiliary knife connecting rod assembly connected to the auxiliary knife, characterized in that the thread trimming structure also includes a moving knife cam and an auxiliary knife cam, the moving knife cam and the auxiliary knife cam are arranged in parallel and spaced apart and are both fixedly connected to the driving shaft, the moving knife connecting rod assembly has a first abutting portion abutting against the working circumference of the moving knife cam, and the auxiliary knife connecting rod assembly has a second abutting portion abutting against the working circumference of the auxiliary knife cam; The working circumference of the movable knife cam 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, and the first convex arc segment BC has a cutting arc surface which is concentric with the driving shaft; The working circumferential surface of the auxiliary knife cam has a needle starter thread trimming peach tip a and a tail needle thread trimming peach tip c arranged in sequence along the circumferential direction, and the distance between the needle starter thread trimming peach tip a and the tail needle thread trimming peach tip c and the axis of the driving shaft is greater than the distance between the other surfaces and the axis of the driving shaft; When the thread trimming arc surface on the moving knife cam slides over the abutment portion 1, the moving knife stops at a position where the moving knife edge is located directly below the needle drop hole, and in this process, the needle-starting thread trimming peach tip a on the auxiliary knife cam can slide over the abutment portion 2 to make the auxiliary knife move toward the moving knife edge and engage with the moving knife edge of the moving knife; When the second convex arc segment DA on the moving knife cam slides over the abutment portion 1, the tail needle thread trimming peach tip c on the auxiliary knife cam can slide over the abutment portion 2 to make the auxiliary knife move toward the moving knife edge and engage with the moving knife edge of the moving knife.

[0007] In this thread trimming structure, since the moving knife cam and the auxiliary knife cam are fixedly connected to the driving shaft, the moving knife cam and the auxiliary knife cam can be driven to rotate by one motor. This can eliminate the error accumulation that may occur between the two motors when they are driven separately by two motors, and simplify the control algorithm, so that the movement of the moving knife and the auxiliary knife is more coordinated, thereby improving the working stability and reliability of the thread trimming structure.

[0008] 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.

[0009] 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.

[0010] 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: When the thread trimming arc surface on the moving knife cam slides over the abutment part 1, the needle thread trimming peach tip a on the auxiliary knife cam slides over the abutment part 2, so that the auxiliary knife moves toward the moving knife edge and engages with the moving knife edge of the moving knife to cut the needle thread. When the second convex arc segment DA on the moving knife cam slides over the abutment part 1, the tail needle thread cutting peach tip c on the auxiliary knife cam slides over the abutment part 2, so that the auxiliary knife moves toward the moving knife edge and engages with the moving knife edge of the moving knife to cut the tail needle surface thread and the bottom thread.

[0011] In the above-mentioned double-cam sewing machine thread trimming structure, the second convex arc segment DA is an arc surface concentric with the drive shaft, and the distance from the starting needle thread trimming peach tip a to the axis of the drive shaft is equal to the distance from the tail needle thread trimming peach tip c to the axis of the drive shaft. This structure allows the auxiliary knife to swing to the same position when the starting needle thread trimming and the tail needle thread trimming are performed. 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 over the abutment portion 1, the moving knife will also stop at a position where the moving knife edge is located directly below the needle drop hole, and the auxiliary knife can also move to a position that engages with the moving knife edge, so that the thread trimming position is closer to the needle drop hole, so that after sewing, the tail needle surface thread and the bottom thread after cutting are as short as possible, thereby improving the bird's nest sewing effect.

[0012] In the above-mentioned double-cam sewing machine thread trimming structure, the sewing machine further includes a rotary hook, the movable knife swings up and down around the outer circumference of the rotary hook, and the movable knife swings downward when the working circumference of the movable knife cam pushes the abutting portion in a direction away from the axis of the drive shaft. This design utilizes the space around the rotary hook for the movable knife to swing, which is not only compact in structure, but also because the movable knife is always close to the rotary hook, it is convenient to accurately cut the bottom thread on the rotary hook after the sewing work is completed, so that the thread trimming structure works stably and reliably.

[0013] In the above-mentioned double-cam sewing machine thread trimming structure, the movable knife has a lower needle hole, and the movable knife cutting edge is located in front of the lower needle hole along the swinging direction of the movable knife. 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 are both greater than the distance from the thread trimming arc surface to the axis of the drive shaft. When the concave inflection point of the first concave arc segment AB abuts against the abutment portion 1, the lower needle hole on the movable knife and the needle drop hole on the needle plate are directly opposite to each other.

[0014] Before inserting the first stitch, the driving shaft drives the movable knife cam to rotate to the concave turning point of the first concave arc segment AB and abuts against the abutment portion. At this time, the lower needle hole on the movable knife and the needle hole on the needle plate are directly opposite each other. The needle first passes through the lower needle hole downward, then leaves the lower needle hole upward and is lifted to above the needle plate, completing the first stitch insertion action of the needle, and the surface thread on the needle remains in the lower needle hole.

[0015] Then, the driving shaft drives the moving knife cam to rotate. At this time, the first concave arc segment AB will push the abutting part to move away from the axis of the driving shaft, causing the moving knife to swing downward with the needle thread until the starting point B of the first convex arc segment BC abuts against the abutting part. At this time, since the distance from the starting point B to the axis of the driving shaft is greater than the distance from the thread cutting arc surface to the axis of the driving shaft, the position of the moving knife is lower than the position to be cut, and the moving knife can avoid the needle lowering position of the needle, so that the needle lowering will not hit the moving knife.

[0016] After that, the needle performs the second needle insertion action, and the upper thread on the needle is locked with the lower thread in the rotary hook mechanism, and the needle sews the set number of stitches, such as two, three or four stitches. The driving shaft drives the movable knife to continue to swing, and when the trimming arc surface on the first convex arc segment BC abuts against the abutment portion 1, the movable knife stops at a position where its movable knife edge is located directly below the needle drop hole. At this time, the auxiliary knife moves toward the movable knife edge and bites with the movable knife edge of the movable knife, thereby cutting the upper thread.

[0017] After the surface thread is cut, the driving 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 portion. At this time, since the distance from the end point C to the axis of the driving shaft is also greater than the distance from the thread cutting arc surface to the axis of the driving shaft, the moving knife swings downward from the thread cutting position during the process, so that the moving knife can avoid the needle lowering position of the machine needle, so that the needle lowering will not hit the moving knife, and the sewing machine can continue to perform subsequent sewing until the last stitch is completed.

[0018] In the above-mentioned double-cam sewing machine thread trimming structure, the thread trimming structure also includes a thread pressing piece located beside the rotary hook. When the starting point B of the first convex arc segment BC abuts against abutting portion 1, the lower side surface of the movable knife abuts against the thread pressing piece to clamp the suture thread passing through the lower needle hole.

[0019] After completing the first stitch of the needle and lifting the needle upward, the movable knife swings downward with the start-up thread until the starting point B of the first convex arc segment BC abuts against the abutting portion. At this time, the movable knife swings to the lower dead point (i.e. the lowest point). At this position, the lower side surface of the movable knife can abut against the thread pressing plate, clamping the stitch thread passing through the lower needle hole (this stitch thread is the start-up thread), and can position the start-up thread to prevent the start-up thread from flying around at will, making it easier for the movable knife and the auxiliary knife to complete the thread cutting action cleanly and avoid thread cutting failure.

[0020] In the above-mentioned double-cam sewing machine thread cutting structure, the movable knife also has a thread hooking groove located between the movable knife blade and the lower needle hole. When the inward inflection point of the second concave arc segment CD abuts against the abutment portion, the thread hooking groove on the movable knife is directly opposite to the needle hole on the needle plate.

[0021] When the last stitch is completed, the driving shaft rotates with the moving knife cam. In the process of the moving knife cam sticking to the abutment part 1 from the end point C of the first convex arc segment BC to the concave turning point of the second concave arc segment CD, the moving knife will swing upward and rely on the dividing line tip at the front end of the moving knife to push one of the tail needle surface threads in the bottom thread and surface thread loop to the side of the dividing line tip. As the moving knife continues to swing upward, the tail needle surface thread and the bottom thread will slide along the side wall of the moving knife until the concave turning point of the second concave arc segment CD abuts against the abutment part 1, the thread hook groove on the moving knife is exactly opposite to the needle drop hole on the needle plate, and the tail needle surface thread and the bottom thread can enter the thread hook groove smoothly. Afterwards, as the movable knife cam continues to rotate, the movable knife cam sticks to the abutment portion - in the process of reaching the starting point D of the second convex arc segment DA from the concave turning point of the second concave arc segment CD, the movable knife will swing downward, so that the movable knife edge of the movable knife approaches the bottom of the needle drop hole, and at the same time, the movable knife edge of the movable knife also approaches the tail needle surface thread and the bottom thread, making it easier for the auxiliary knife to approach and cut the tail needle surface thread and the bottom thread.

[0022] In the above-mentioned double-cam sewing machine thread trimming structure, the length of the second convex arc segment DA is less than the length of the first convex arc segment BC. Since the movable knife remains stationary during the process of the second convex arc segment DA sliding over the abutment portion 1, the second convex arc segment DA is only used to cut the tail needle surface thread and the bottom thread. At this time, the length of the second convex arc segment DA is short relative to the length of the first convex arc segment BC, which can complete the sewing work. After the tail needle surface thread and the bottom thread are cut, the movable knife can quickly reset to the initial state and wait for the next sewing work, which can improve the thread trimming efficiency and the working efficiency of the sewing machine.

[0023] In the above-mentioned double-cam sewing machine thread trimming structure, the auxiliary knife swings up and down around the outer circumference of the rotary shuttle, and when the working circumference of the auxiliary knife cam pushes the abutment part to move in the direction away from the axis of the driving shaft, the auxiliary knife swings upward; the working circumference of the auxiliary knife cam also has a thread trimming peach tip b, and the starting needle thread trimming peach tip a, the thread trimming peach tip b and the tail needle thread trimming peach tip c are arranged in sequence along the working circumference of the auxiliary knife cam.

[0024] Because when the second convex arc segment DA on the moving knife cam slides over the abutment portion 1, the tail needle thread cutting peach tip c on the auxiliary knife cam can slide over the abutment portion 2, so that the auxiliary knife moves toward the moving knife edge and bites with the moving knife edge of the moving knife, and the tail needle upper thread and the lower thread are cut. Therefore, before cutting the tail needle upper thread and the lower thread, the thread cutting peach tip b will slide over the abutment portion 2, so that the auxiliary knife can move close to the thread cutting position in advance, instead of instantly approaching the moving knife from a far position to cut the thread. This design can improve the thread cutting stability of the auxiliary knife, improve the thread cutting effect, and avoid the phenomenon of thread pulling or uneven breakage.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] Compared with the prior art, the double cam sewing machine thread trimming structure has the following advantages: 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.

[0029] 2. In this thread trimming structure, since the moving knife cam and the auxiliary knife cam are both fixedly connected to the driving shaft, the moving knife cam and the auxiliary knife cam can be driven to rotate by one motor, which can eliminate the error accumulation that may occur between the two motors when they are driven separately by two motors, and simplify the control algorithm, so that the movement of the moving knife and the auxiliary knife is more coordinated. In addition, since the geometric shapes of the moving knife cam and the auxiliary knife cam are pre-designed and both are driven by the same driving shaft, the respective positions of the moving knife and the auxiliary knife and the matching relationship between the two depend on the rotation angle of the driving shaft. That is to say, when the motor drives the driving shaft to rotate to a specific angle, the moving knife and the auxiliary knife will reach the corresponding position and form a corresponding matching relationship. This design enables the moving knife and the auxiliary knife to perform actions such as thread trimming and resetting after thread trimming more accurately, thereby improving the working stability and reliability of the thread trimming structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a structural schematic diagram of the thread trimming structure installed on the machine base.

[0031] Figure 2 It is a three-dimensional structural schematic diagram of the wire cutting structure.

[0032] Figure 3 It is a schematic diagram of the transmission structure of the moving knife.

[0033] Figure 4 It is a three-dimensional structural diagram of the moving knife cam.

[0034] Figure 5 It is a schematic diagram of the corresponding parts of the working surface of the moving knife cam.

[0035] Figure 6 It is a schematic diagram of the auxiliary knife cam.

[0036] Figure 7 It is a front view of the thread trimming structure in an initial state.

[0037] Figure 8 It is a partial schematic diagram of the thread trimming structure in an initial state.

[0038] Fig. 9 It is a schematic diagram of the motion relationship between the moving knife cam and the auxiliary knife cam when the thread trimming structure is in the initial state.

[0039] Fig.10 It is a front view of the thread trimming structure when it is in the thread pressing state.

[0040] Fig.11 It is a schematic diagram of the motion relationship between the moving knife cam and the auxiliary knife cam when the thread trimming structure is in the thread pressing state.

[0041] Fig.12It is a front view of the process of the thread trimming structure cutting the needle thread.

[0042] Fig.13 It is a partial schematic diagram of the process of cutting the needle thread of the thread cutting structure.

[0043] Fig.14 The present invention is a schematic diagram of the motion relationship between the moving knife cam and the auxiliary knife cam in the process of cutting the needle thread of the thread trimming structure.

[0044] Fig.15 It is a front view of the thread-hooking state process of the thread trimming structure.

[0045] Fig.16 It is a partial schematic diagram of the thread-hooking state process of the thread trimming structure.

[0046] Fig.17 It is a schematic diagram of the motion relationship between the moving knife cam and the auxiliary knife cam during the thread hooking state of the thread trimming structure.

[0047] Fig.18 It is a front view of the process of the thread trimming structure cutting off the upper thread and the lower thread of the tail needle.

[0048] Fig.19 It is a partial schematic diagram of the process of the thread cutting structure cutting off the tail needle upper thread and the lower thread.

[0049] Fig. 20 The present invention is a schematic diagram of the motion relationship between the moving knife cam and the auxiliary knife cam in the process of cutting the tail needle upper thread and the lower thread of the thread trimming structure.

[0050] In the figure, 1, machine base; 2, needle plate; 21, needle drop hole; 3, moving knife; 31, moving knife edge; 32, lower needle hole; 33, thread hook groove; 4, auxiliary knife; 41, auxiliary knife edge; 5, driving shaft; 6, moving knife connecting rod assembly; 61, abutment part 1; 7, auxiliary knife connecting rod assembly; 71, abutment part 2; 8, moving knife cam; 81, thread trimming arc surface; 9, auxiliary knife cam; 10, rotary shuttle; 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 DESCRIPTION

[0051] The following is a specific embodiment of the present invention and combined with the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to this embodiment.

[0052] like Figure 1 and Figure 2As shown, in the thread trimming structure of the double cam sewing machine, the sewing machine includes a machine base 1, a rotary hook 10 and a needle plate 2 with a needle drop hole 21. The thread trimming structure includes a moving knife cam 8, an auxiliary knife cam 9, a thread pressing 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 surface of the auxiliary knife 4 near one end of the needle forms an auxiliary knife edge 41. Further, the machine base 1 is also provided with a driving shaft 5, a moving knife connecting rod assembly 6 connected to the moving knife 3, and an auxiliary knife connecting rod assembly 7 connected to the auxiliary knife 4. 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 bottom of the frame is fixedly connected with a servo motor 12 that can drive the driving shaft 5 to rotate.

[0053] like Figure 2 and Figure 3 As shown, the movable knife connecting rod assembly 6 and the auxiliary knife connecting rod assembly 7 both include an annular knife holder 13, a lower connecting rod 14 and an upper connecting rod 15. The movable knife 3 and the auxiliary knife 4 are respectively mounted on the corresponding knife holder 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 sewing machine hook 10. In the movable knife connecting rod assembly 6, one end of the upper connecting rod 15 is hinged to the knife holder 13 corresponding to the movable 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 movable knife connecting rod assembly 6 has a contact portion 61 that contacts the working circumference of the movable knife cam 8. When the servo motor 12 drives the driving shaft 5 to rotate, the movable knife 3 can be driven to swing up and down around the outer circumference of the rotary shuttle 10 by relying on the movable knife cam 8 and the movable knife connecting rod assembly 6 for power transmission, and the movable knife 3 can be driven to swing up and down around the outer circumference of the rotary shuttle 10, and when the working circumferential surface of the movable knife cam 8 pushes the abutment portion 61 to move in the direction away from the axis of the driving shaft 5, the movable knife 3 swings downward, and vice versa.

[0054] like Figure 2 As shown, in the auxiliary knife connecting rod assembly 7, one end of the 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 the hinge shaft 16. The middle part of the lower connecting rod 14 of the auxiliary knife connecting rod assembly 7 has a second abutment portion 71 that abuts against the working circumference of the auxiliary knife cam 9. When the driving 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 periphery of the rotary shuttle 10 above the thread pressing piece 11 by power transmission by the auxiliary knife cam 9 and the auxiliary knife connecting rod assembly 7, and when the working circumference of the auxiliary knife cam 9 pushes the second abutment 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.

[0055] like Figure 4 and Figure 5As shown, the working circumference of the movable 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 which are connected end to end in sequence. Figure 5 From the perspective, the driving shaft 5 drives the movable knife cam 8 to rotate clockwise in a 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 sequentially slide over the abutment portion 61. The auxiliary knife cam 9 and the movable knife cam 8 rotate synchronously and in the same direction.

[0056] Specifically, 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 shear arc surface 81 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 center of the drive shaft 5 are both greater than the distance from the shear arc surface 81 to the axis center of the drive shaft 5.

[0057] like Figure 6 As shown, the working circumference of the auxiliary knife cam 9 has a needle thread cutting peach tip a, a to-be-cut peach tip b and a tail needle thread cutting peach tip c arranged in sequence along the circumferential direction, the distance from the needle thread cutting peach tip a to the axis of the drive shaft 5 is equal to the distance from the tail needle thread cutting peach tip c to the axis of the drive shaft 5, and the distances from the 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 remaining surfaces to the axis of the drive shaft 5 except the two, and of course, are greater than the distance from the to-be-cut peach tip b to the axis of the drive shaft 5. The needle thread cutting peach tip a and the to-be-cut peach tip b are connected by a connecting concave arc segment ab, the surface of the to-be-cut peach tip b is an arc surface concentric with the drive shaft 5, the to-be-cut peach tip b and the tail needle thread cutting peach tip c are smoothly transitionally connected, and the tail needle thread cutting peach tip c and the needle thread cutting peach tip a are connected by a connecting convex arc segment ca.

[0058] The thread trimming method of the thread trimming structure comprises the following steps: 1. Initial state: Figure 7 , Figure 8 and Fig. 9 As shown, before the first needle is inserted, the driving shaft 5 drives the movable knife cam 8 to rotate to the concave turning point of the first concave arc segment AB and abut against the abutment part 1 61. At this time, the lower needle hole 32 on the movable knife 3 is directly opposite to the needle hole 21 on the needle plate 2, and the front half of the connecting convex arc segment ca on the auxiliary knife cam 9 abuts against the abutment part 2 71, so that the position of the auxiliary knife 4 is lower than the thread cutting position to avoid the needle insertion track. The needle first passes through the lower needle hole 32 on the movable knife 3 downward, then leaves the lower needle hole 32 upward and is lifted above the needle plate 2, completing the first needle insertion action of the needle, and the upper thread on the needle remains in the lower needle hole 32.

[0059] 2. Pressing line: Fig.10 and Fig.11As shown, after the first needle insertion action of the machine needle is completed and the machine needle is lifted upward, the driving shaft 5 continues to drive the movable knife cam 8 to rotate. At this time, the second half of the first concave arc segment AB will push the abutment portion 61 to move away from the axis of the driving shaft 5, so that the movable knife 3 swings downward with the needle thread until the starting point B of the first convex arc segment BC abuts against the abutment portion 61. At this time, the movable knife 3 swings to the lower dead point, and the lower side surface of the movable knife 3 abuts against the thread pressing sheet 11 to clamp the needle thread passing through the lower needle hole 32. In this process, the auxiliary knife 4 will also swing downward for a stroke to avoid the movable knife 3 from biting with the movable knife 3 and cutting the surface thread in advance during the downward swing of the movable knife 3.

[0060] 3. Cut the upper thread: The needle starts the second stitch, and the upper thread on the needle is locked with the lower thread in the rotary hook 10 mechanism. After the needle sews the set number of stitches, such as two, three or four stitches, the drive shaft 5 drives the movable knife 3 to continue to swing. Fig.12 , Fig.13 and Fig.14 As shown, when the thread trimming arc surface 81 on the first convex arc segment BC slides over the abutment portion 1 61, the movable knife 3 stops at a position where its movable knife edge 31 is located directly below the needle drop hole 21, and in this process, the needle thread trimming peach tip a on the auxiliary knife cam 9 can slide over the abutment portion 2 71 to make the auxiliary knife 4 move toward the movable knife edge 31 and engage with the movable knife edge 31 of the movable knife 3 to cut the needle thread. In addition, in this process, before the needle thread is cut, the suction pipe 17 is already in the suction state and the thread pressing piece 11 has released the needle thread, so that the cut needle thread head is directly sucked away by the suction pipe 17.

[0061] 4. Continue sewing: After the needle thread is cut, the drive shaft 5 continues to drive the movable 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 abutment part 1 61, and the auxiliary knife cam 9 slides from the needle thread cutting peach tip a to the concave turning point connecting the concave arc segment ab along the abutment part 2 71. In this process, the movable knife 3 and the auxiliary knife 4 are both swung downward from the thread cutting position, so that the movable knife 3 and the auxiliary knife 4 can avoid the needle lowering position of the machine needle, and the needle lowering will not hit the movable knife 3 and the auxiliary knife 4, so that the sewing machine continues to perform subsequent sewing until the last stitch is sewn.

[0062] 5. Line drawing: Fig.15 , Fig.16 and Fig.17As shown, when the last stitch is completed, the driving shaft 5 rotates with the moving knife cam 8 and the auxiliary knife cam 9. When the moving knife cam 8 is close to the abutment part 1 61 from the end point C of the first convex arc segment BC to the concave turning point of the second concave arc segment CD, the moving knife 3 will swing upward and rely on the line dividing tip at the front end of the moving knife 3 to push one of the tail needle surface threads in the bottom line and the surface thread loop to the side of the line dividing tip. When the moving knife 3 continues to swing upward, the tail needle surface thread and the bottom line will slide along the side wall of the moving knife 3 until the concave turning point of the second concave arc segment CD abuts against the abutment part 1 61, and the thread hooking groove 33 on the moving knife 3 is aligned with the needle drop hole 21 on the needle plate 2. At this time, the tail needle surface thread and the bottom line can smoothly enter the thread hooking groove 33. In this process, the auxiliary knife cam 9 slides from the concave turning point connecting the concave arc segment ab close to the abutment part 2 71 to the direction of the peach tip b to be cut, so that the auxiliary knife 4 swings upward to the position to be cut.

[0063] 6. Cutting the tail needle surface thread and the bottom thread: The moving knife cam 8 and the auxiliary knife cam 9 continue to rotate. When the moving knife cam 8 is close to the abutment part 1 61 from the concave turning point 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 moving knife edge 31 of the moving knife 3 is close to the lower part of the needle drop hole 21, and the moving knife edge 31 of the moving knife 3 is also close to the tail needle surface thread and the bottom thread. In this process, the auxiliary knife cam 9 slides close to the peach tip b to be cut. Since the surface of the peach tip b to be cut is a circular arc surface concentric with the driving shaft 5, the auxiliary knife 4 stops and waits for cutting when the peach tip b to be cut slides over the abutment part 2 71.

[0064] As the moving knife cam 8 and the auxiliary knife cam 9 continue to rotate, Fig.18 , Fig.19 and Fig. 20 As shown, in the process that the second convex arc segment DA on the moving knife cam 8 slides over the abutment part 1 61, the tail needle thread cutting peach tip c on the auxiliary knife cam 9 can slide over the abutment part 2 71, so that the auxiliary knife 4 moves toward the moving knife edge 31 and engages with the moving knife edge 31 of the moving knife 3 to cut the tail needle surface thread and the bottom thread. In 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 over the abutment part 1 61, the moving knife 3 will also stop at a position where its moving knife edge 31 is located directly below the needle drop hole 21, so that the thread cutting position is closer to the needle drop hole 21, so that after sewing, the tail needle surface thread and the bottom thread after cutting are as short as possible, thereby improving the bird's nest sewing effect.

[0065] 7. Reset: The moving knife cam 8 and the auxiliary knife cam 9 continue to rotate, so that the moving knife 3 and the auxiliary knife 4 are reset to the Figure 7 , Figure 8 and Fig. 9Of course, in the actual sewing process, the movable knife 3 and the auxiliary knife 4 can be reset to other positions. When the sewing machine is started for the next sewing, the control system controls the servo motor 12 to move so that the movable knife 3 and the auxiliary knife 4 first swing to the position shown in the figure. Figure 7 , Figure 8 and Fig. 9 The initial state is shown.

[0066] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

[0067] Although the following terms are used more frequently in this article, such as 1, base; 2, needle plate; 21, needle drop hole; 3, moving knife; 31, moving knife edge; 32, lower needle hole; 33, thread hook groove; 4, auxiliary knife; 41, auxiliary knife edge; 5, driving shaft; 6, moving knife connecting rod assembly; 61, abutment part 1; 7, auxiliary knife connecting rod assembly; 71, abutment part 2; 8, moving knife cam; 81, thread trimming arc surface; 9, auxiliary knife cam; 10, rotary shuttle; 11, thread pressing piece; 12, servo motor; 13, knife holder; 14, lower connecting rod; 15, upper connecting rod; 16, hinge shaft; 17, air suction pipe, etc., the possibility of using other terms is not excluded. These terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional restrictions 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, and the first convex arc segment BC has a cutting arc surface (81) which is concentric with 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); 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 thread cutting arc surface (81) to the axis of the drive shaft (5); when the inner concave inflection 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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