Lockstitch sewing machine with function to prevent incorrect stitching

Abstract

To prevent a hitch stitch from occurring and remarkably improve sewing performance and significantly improve quality of a sewn product.SOLUTION: In a lock stitch sewing machine, a needle rotates at an arbitrary angle on a flat surface perpendicular to a driving direction during a period from a phase in which the needle 5 passes through a sewn product to a top dead center phase of the needle, and returns to an original attitude position of the needle by reversely rotating during a period from a phase in which the needle is almost stuck in the sewn product to a bottom dead center phase of the needle.SELECTED DRAWING: Figure 20

Description

[Technical field]

[0001] This technology relates to the structure of sewing machines and sewing techniques. Summary of the Invention Problems to be Solved by the Invention

[0002] Conventionally, hitch stitches, as shown in Figure 1, which have a detrimental effect on the quality of stitching, which greatly affects the quality of sewn products, have been accepted as "a phenomenon that does not occur continuously but occurs occasionally, and when the sewing thread slackens, it becomes unruly, and the uncontrollable thread unruly affects the stitching, so it is an unpredictable and uncontrollable sudden phenomenon," and quality control has been based on an evaluation standard of a certain number of hitch stitches per certain length. A normal stitch (perfect stitch) is shown in Figure 2. Means to solve the problem

[0003] The present invention theoretically analyzes the mechanism by which imperfect stitches occur, and prevents the occurrence of imperfect stitches by changing and controlling the thread paths (thread paths) of the upper and lower threads under sewing conditions that cause imperfect stitches.

[0004] In the case of an incorrect stitch (hitch stitch) shown in Figure 1, the upper thread 1 is wrapped around the lower thread 2 by half a turn compared to the normal stitch (perfect stitch) shown in Figure 2. The occurrence of an incorrect stitch significantly reduces the quality of the sewn product by causing variations in the sewing force, disturbing the stitch line, and sometimes causing sewing thread breakage, etc., in terms of sewing performance, such as "upsetting the tension balance of the stitches," "causing thread breakage," "affecting the mutual supply of thread between stitches," and "variation in the amount of thread between stitches."

[0005] In conventional sewing machines, hitch stitches had to be accepted as an "uncontrollable, sudden phenomenon." However, the present invention elucidates the mechanism by which hitch stitches occur, and based on that, establishes a method for preventing hitch stitches from occurring, significantly improving sewing performance and, ultimately, the quality of sewn products.

[0006] The mechanism by which imperfect stitches occur will be explained.

[0007] The arrangement of the shuttle 3 in a lockstitch sewing machine can be classified into a side shuttle type (see Figure 3), in which the drive direction of the shuttle blade point 4 is parallel to the sewing direction (fabric feed direction), and a front shuttle type (see Figure 4), in which the shuttle blade point 4 is perpendicular to the sewing direction (fabric feed direction).

[0008] In addition, depending on the function of the hook tip 4, the hook 3 can be classified into a shuttle type hook, in which the hook tip 4 passes through the upper thread loop 8 together with the bobbin 7 storing the lower thread 2, and a hook type hook, in which the hook tip 4 only assists the bobbin 7 to pass through the upper thread loop 8, but does not pass through the upper thread loop 8.

[0009] The behavior of the upper thread 1 and lower thread 2 during the stitch formation process is almost the same whether it is a side hook type, front hook type, shuttle type hook or hook type hook. Therefore, we will explain the stitch formation process (normal stitch) with a side hook type and shuttle type hook, and the mechanism of occurrence of imperfect stitches with a front hook type and shuttle type hook.

[0010] Figures 5 to 8 show the process of stitch formation (normal stitch), and Figure 8A shows an enlarged view of the entanglement of the upper and lower threads that form the stitch.

[0011] Figures 9 to 12 show the process of forming an incorrect stitch, and Figure 12B shows an enlarged view of the tangle of the upper and lower threads that form the stitch.

[0012] From the explanatory diagram of the process of forming both stitches, it can be seen that when the needle 5 (needle thread loop) passes on the right side of the lower thread 2 that connects from the bobbin 7 to the previous stitch 9, it becomes a normal stitch (perfect stitch), and when it passes on the left side, it becomes an incorrect stitch (hitch stitch).

[0013] There is an illegal stitch (hitch stitch) that cannot be explained by the above stitch formation process. It occurs frequently in backstitching with a front-hook machine. With a front-hook machine, if the needle 5 passes to the right of the upper thread 1 that connects from the previous stitch 9 to the needle thread eye 6, it is a normal stitch (perfect stitch), and if it passes to the left, it is an illegal stitch (hitch stitch). This illegal stitch is normally called an "upper thread hitch." Figure 13 is an explanatory diagram of the entanglement of the upper and lower threads in backstitching with a front-hook machine, showing a normal stitch and Figure 14 an illegal stitch.

[0014] The above two types of incorrect stitches (hitch stitches) seem to be different phenomena, however, an analysis of the mechanism by which incorrect stitches occur, which is the basis of this invention, has revealed that the mechanism by which both types of incorrect stitches occur is the same, and that this is determined by the path of the lower thread 2 that connects from the previous stitch 9 to the bobbin 7, and the path of the upper thread 1 that connects from the previous stitch 9 to the needle thread eye 6.

[0015] Figure 15 is an explanatory diagram of a normal stitch (perfect stitch), showing the state of the needle 5 and the needle eye 6 as seen from above, and the paths of the upper thread 1 and lower thread 2. The needle 5 is shown penetrating the fabric. I to V are the positions of the previous stitch 9. Position I is the position of the stitch 9 before the forward stitch of the front hook, and the needle entry point is to the right of the lower thread 2. In this state, if the previous stitch 9 is rotated left so that the upper and lower threads do not cross the needle 5, II is the position of the forward stitch of the side hook (position in Figure 5), III is the position of the stitch 9 before the backstitch of the front hook, and the needle 5 passes to the right of the upper thread 1. IV is the position of the stitch 9 before the backstitch of the side hook, and the upper thread 1 is wrapped around the needle 5 as shown in Figure 16. V is the position of the previous stitch 9 that occurs in zigzag stitching and cycle sewing machines. A normal stitch (perfect stitch) in this position can also be obtained in Figure 17 by rotating I to the right.

[0016] Figure 18 is an explanatory diagram of an incorrect stitch (hitch stitch), showing the state of the needle 5 and needle eye 6 as seen from above, and the paths of the upper thread 1 and lower thread 2, with the needle 5 penetrating the fabric. I to V are the positions of the previous stitch 9. Position I is the position of the stitch 9 before the forward stitch in the front hook, and the needle entry point is to the left of the lower thread 2. In this state, if the previous stitch 9 is rotated to the right so that the upper and lower threads do not cross the needle 5, V is the position of the previous stitch 9 that occurs in zigzag stitching and cycle sewing machines, IV is the position of the stitch 9 before the backstitch in the side hook, and the upper thread 1 is connected in a straight line from the needle eye 6 to the position of the previous stitch 9 as shown in Figure 19. III is the position of the stitch 9 before the backstitch in the front hook, and the needle 5 passes to the left of the upper thread 1. II is the position of the stitch 9 before the forward stitch in the side hook.

[0017] Here, the question is why the occurrence of hitch stitches is less frequent in the backstitching of the side hook than in the backstitching of the front hook. The upper thread path from the needle thread hole 6 to the previous stitch 9 is more natural in IV of Fig. 18 than in IV of Fig. 15. This phenomenon occurs when the upper thread 1, which becomes loose as the needle 5 descends, falls to the left due to the thread twist, and this phenomenon results in the upper thread 1 being wrapped around the needle 5, resulting in the thread path shown in IV of Fig. 15.

[0018] So why does a hitch stitch occur with a front-facing hook? This is due to the relationship between the orientation of the needle thread hole 6 and the drive plane of the thread take-up lever. The slack in the upper thread 1 caused by the needle's downward movement occurs at the same time as the upper thread 1 is loosened by the downward movement of the thread take-up lever. This slack in the upper thread 1 is absorbed by the thread take-up spring. In a front-facing hook type, where the needle thread hole 6 is oriented parallel to the drive plane of the thread take-up lever, the slack in the thread caused by the needle 5's downward movement is absorbed by the thread take-up spring without resistance, but in a side-facing hook, the needle thread hole 6 is oriented perpendicular to the drive plane of the thread take-up lever, so there is only a slight resistance and the slack in the upper thread 1 is absorbed later than the slack in the upper thread 1 loosened by the thread take-up lever. During that time, the slack in the upper thread 1 from the needle thread hole 6 to the previous stitch 9 is greater than in a front-facing hook, causing the slack to fall over.

[0019] In this way, the occurrence of an incorrect stitch is determined by the path of the lower thread 2 that connects from the previous stitch 9 to the bobbin 7 and the path of the upper thread 1 that connects from the previous stitch 9 to the thread eye 6 of the needle.

[0020] The present invention is devised to provide a function for changing the paths of the upper thread 1 and the lower thread 2 to paths that result in a normal stitch under sewing conditions that result in the position of the previous stitch 9 where there is a possibility of an incorrect stitch occurring.

[0021] The first function is to rotate the needle 5 so that the needle thread 1 leading from the needle thread hole 6 to the position of the previous stitch 9 is in a natural state after the needle 5 rises and passes through the fabric, as shown in Fig. 20, and then rotate the needle 5 in the reverse direction to return the needle thread loop 8 to the correct position (the position before rotation) where it is captured by the hook point 4, between the time when the needle 5 descends and penetrates the fabric again and the time when it reaches the bottom dead point of the needle bar, thereby preventing an incorrect stitch. In other words, by rotating the needle 5, the needle thread 1 is wound around the needle 5, creating the V state in Fig. 15. This is the function of [Claim 1].

[0022] The second function is that "when the needle 5 (needle thread loop) passes on the right side of the bobbin thread 2 that connects from the bobbin 7 to the previous stitch 9, a normal stitch (perfect stitch) is produced, but when it passes on the left side, an incorrect stitch (hitch stitch) is produced," so that the bobbin thread handling piece member 10 is actuated as the needle 5 passes the fabric as shown in Figure 21, changing the path of the bobbin thread 2 that connects from the bobbin 7 to the previous stitch 9, and the needle 5 is made to pass on the "right side" of this changed bobbin thread path, thereby preventing an incorrect stitch. In other words, the state of Figure 17 is produced. This is the function of [Claim 2].

[0023] In Figure 21, the hook lower thread exit 11 is shown, which is not shown in the stitch formation explanatory diagrams from Figure 5 to Figure 12, but in reality, in each type of hook, the hook lower thread exit 11 is installed as a thread path for the lower thread, and the relative position of the needle 5 and the hook lower thread exit 11 varies depending on the hook type, and generally, as shown in Figure 13 and subsequent figures, the hook lower thread exit 11 is located in front of the needle 5, to the left. The hook lower thread exit 11 is not shown in the stitch formation explanatory diagrams from Figure 5 to Figure 12 because the route of the lower thread 2 via the hook lower thread exit 11 does not affect the explanation of stitch formation, and therefore the explanation has been simplified to make it easier to understand. An example of an actual hook installation is shown in Figure 22.

[0024] Also, in Figure 21, there is a concern that the operation and shape of the lower thread handling piece member 10 may cause interference with the needle 5 as it passes through, but the explanation that "when the needle 5 (needle thread loop) passes to the right of the lower thread 2 that connects from the bobbin 7 to the previous stitch 9, it is a normal stitch (perfect stitch)" can also be said from the explanations so far that "when the lower thread 2 that connects from the bobbin 7 to the previous stitch 9 passes behind the needle 5 (needle thread loop), it is a normal stitch (perfect stitch)", and this can be avoided by having the lower thread handling piece member 10 move in the direction of movement of the lower thread handling piece member 11, from arrow 13 to arrow 14, as shown in Figure 23, which is viewed from above the needle.

[0025] The movement path and shape of the lower thread separating member 10 vary depending on the type of the shuttle and the position of the shuttle's lower thread outlet 11, but all of these are within the scope of the present invention and will not be described in this description.

[0026] Although both the first and second functions can prevent hitch stitches independently, depending on the position of the previous stitch 9, there is a possibility that excessive load may be applied to the thread path, i.e., the upper thread 1 or the lower thread 2, which may adversely affect the sewing quality. This is due to the correlation and angle between the position of the previous stitch 9 and the direction of the needle thread eye 6. For this reason, better sewing quality can be obtained by switching between the first and second functions depending on the angle of the position of the previous stitch 9 relative to the needle thread eye 6. This is the function of [Claim 3]. [Brief description of the drawings]

[0027] [Figure 1] This is a diagram of an incorrect stitch (hitch stitch). [Diagram 2] This is a diagram of a perfect stitch. [Diagram 3] The figure shows the concept of a side-mounted kettle. [Figure 4] The figure shows the concept of a front-type kettle. [Diagram 5] This is an explanatory diagram of the stitch formation process (normal stitch) (1) [Figure 6] This is an explanatory diagram of the stitch formation process (normal stitch) (2) [Figure 7] This is an explanatory diagram of the stitch formation process (normal stitch) (3) [Figure 8] is an explanatory diagram of the stitch formation process (normal stitch) (4), and A is an enlarged view of the entanglement of the upper and lower threads that form the stitch. [Figure 9] The diagram shows the process of forming irregular stitches (1). [Figure 10] The diagram shows the process of forming irregular stitches (2). [Figure 11] This is an explanatory diagram of the process of forming irregular stitches (3). [Figure 12] A is an explanatory diagram of the process of forming an incorrect stitch (4), and B is an enlarged view of the entanglement of the upper and lower threads that form the stitch. [Figure 13] This is an explanatory diagram of the tangle of the upper and lower threads in a normal backstitch with a front bobbin type sewing machine. [Figure 14] This is an explanatory diagram of the tangle of upper and lower threads in an incorrect stitch when backstitching with a front bobbin type sewing machine. [Figure 15] This is an explanatory diagram of a perfect stitch (1) [Figure 16] is an explanatory diagram of the state of needle 5 and needle thread 1 at IV in Fig. 15. [Figure 17] A diagram of a perfect stitch (2) [Figure 18] This is an explanatory diagram of an incorrect stitch (hitch stitch) [Figure 19] is an explanatory diagram of the state of needle 5 and needle thread 1 at IV in Fig. 18. [Figure 20]This is an explanatory diagram of how to rotate the needle to get a perfect stitch. [Figure 21] FIG. 1 is an explanatory diagram of a state in which the lower thread separating member 10 is in operation. [Figure 22] This is an example of the bobbin thread outlet 11 of the hook being installed in an actual hook. [Diagram 23] 1 is an explanatory diagram of the operation of the lower thread separating member 10. [Explanation of symbols]

[0028] 1... Upper thread, 2... Lower thread, 2'... Lower thread when thread handling member 10 is not operating, 3... Hook, 4... Hook blade point, 5... Needle, 5'... Needle in middle position for zigzag stitching, 5"... Needle in left position for zigzag stitching, 6... Needle thread hole, 7... Bobbin, 8... Upper thread loop, 9... Previous stitch, 10... Lower thread handling member, 11... Lower thread outlet of hook, 12... Thread hole in needle plate, 13... Direction of movement of thread handling member, 14... Direction of movement of thread handling member

Claims

1. This lockstitch sewing machine has a needle rotation function, which detects the previous stitch position, rotates the needle on a plane perpendicular to the drive direction by an arbitrary angle related to the previous stitch position between the phase where the needle leaves the sewing material and the top dead point phase of the needle, and rotates in the opposite direction between the phase where the needle almost pierces the sewing material and the bottom dead point phase of the needle to return to the original needle posture and position.

2. This lockstitch sewing machine has a bobbin thread path changing function having a bobbin thread handling piece member for changing the thread path of the bobbin thread leading from the previous stitch to the bobbin until the needle penetrates the fabric and reaches the bottom dead point, detects the previous stitch position, and automatically selects whether to operate the bobbin thread path changing function or not depending on the relative position between the previous stitch position and the position of the needle about to form the stitch.

3. A lock stitch sewing machine having a function of automatically selecting and operating the function of claim 1 or the function of claim 2 depending on the relative position of the needle about to form a stitch and the previous stitch.

Images