[4] BACKGROUND ART [5] Generally, in the sewing machine, there is provided a rotary shuttle device 100 for supplying the lower thread. The rotary shuttle device 100 is disposed at a driving shaft 10 which is rotatably connected to a driving apparatus, and comprised of a hook body 20, a bobbin case BC accommodated in the hook body 20 and a bobbin 40 on which the lower thread is wound. The bobbin case BC comprises a bobbin case base 30 ac- commodated in the hook body 20 and a bobbin case body 50 for receiving the bobbin 40 from an outside of the bobbin 40.

[6] At a bottom of the bobbin case base 30, there is upright disposed a stud 31. The bobbin 40 is rotatably disposed at the stud 31. A track groove 21 is formed in an inner side of the hook body 20. A hook 22 is formed at an end of the hook body 20. In the vicinity of the hook 22, there is formed a groove 23 having a gentle radius of curvature so that the lower thread is passed through the groove 23, while being contacted with the groove 23. On an outer side of the bobbin case base 30 is formed a track portion 32 which is inserted into the track groove 21 of the hook body 20 so that the bobbin case base 30 is disposed in the hook body 20 and the hook body 20 is also capable of being rotated. Meanwhile, a semicircular gib 25 is fixed to one half portion of an outside portion of the hook body 20 by fastening means such as a bolt so that the bobbin case base 30 can be rotatably disposed and the bobbin case base 30 can be inserted therein or separated therefrom. The gib 25 has a hook 25a opposite to the hook 22 formed at the hook body 20. Further, a thread guide 26 is removably fixed to the other half portion of the outside portion of the hook body 20 by the fastening means such as the bolt so as to be continuous with the gib 25. The thread guide 26 also has a hook 26a opposite to the hook 25a of the gib 25.

[7] The bobbin case base (hereinafter, called base) 30 and the bobbin case body (hereinafter, called body) 20 are integrally coupled to each other to form the bobbin case BC. A bracket (not shown) which is adjacent to the bobbin case BC and disposed at a body of the sewing machine is inserted into a concaved portion 33 formed at the base 30 so as to position the bobbin case BC, so that the bobbin case BC is fixedly positioned. Furthermore, in the vicinity of the concaved portion 33, there is formed a through-hole 34 through which a sewing needle is passed when the needle is moved down.

[8] The bobbin 40 comprises a winding shaft 41 on which the lower thread is wound, a first flange 43 formed at one end of the winding shaft 41 and a second flange 45 formed at the other end of the winding shaft 41. Meanwhile, an extended bobbin which further extends the winding shaft 41 and has a partition flange 47 in which a recessed portion having a slope is formed between the first and second flanges 43 and 45 has been filed by the applicant.

[9] Now, an operation of the rotary shuttle device as described above will be described below.

[10] When the sewing machined is operated, the hook body 20 is rotated, and at the same time, a thread take-up lever (not shown) of upper thread and the needle are moved up and down. During two revolutions of the hook body, the needle hooks up the lower thread once. Due to a thread taking-up operation, a desired length of thread is pulled so as to prepare for a next lower thread hooking-up operation.

[11] FIG. 2 is a view in which the bobbin case BC and the bobbin 40 are omitted so as to show a status that the upper thread 3 threaded through the needle 2 is hooked on the hook body 20, when the needle 2 is moved down, FIG. 3 is a view showing a moment that the upper thread is hooked by the hook body 20, and FIG. 4 is a side view of FIG.

3.

[12] Furthermore, FIGs 5 to 10 show in turn a sewing operation, and a), b), c), d), e) and f) of each drawings are views from a front of the rotary shuttle device, and a'), b'), c'), d'), e') and f) are views showing a status that the hook body 10 is reversed so that a bottom of the hook body 20 is directed upward to help the understanding.

[13] If the sewing machine is operated, the needle through which the upper thread 3 is threaded is moved down. At the same tiem, the upper thread is hooked down by the hook 22, while the hook body 20 is rotated with a descent of the needle (referring to FIGs. 2 to 6). Since a slit 2a is formed at a side of the needle 2 so that the upper thread threaded through the needle can be hooked down by the hook 22 of the hook body 20, the above operation can be performed. At this time, if a distance between the needle 2 and the hook 22 is far away, since the upper thread 3 is not hooked onto the hook 22, a sewn line is omitted at times or a sewing operation is not normally performed. If the distance is too close, since the needle is collided with the hook 22, the needle is broken.

[14] As described above, the upper thread 3 hooked down by the hook 22 of the hook body 20 is guided by the thread guide 26 of the hook body 20 so as to form a loop for wrapping the bobbin case BC, thereby hooking up the lower thread 4 (FIGs. 7 to 10).

As described above, the reason why the upper thread 3 can warp the bobbin case BC and form the loop is because the upper thread 3 is previously pulled by the thread take- up lever in the previous stroke.

[15] The length of upper thread pulled by the thread take-up lever, while the thread take- up lever is reciprocated once, is coincident with a length of the upper thread required to wrap the bobbin case BC while the hook body 20 makes one revolution. If a volume of the hook body 20 closely related with a volume of the lower thread is increased, the length of the upper thread pulled by the thread take-up lever is short so that the thread is broken. If the length is too long, a tension of the lower thread is not kept, whereby the lower thread is dangled down and fluttered roughly on the sewn line.

[16] If a winding amount of the lower thread is increased, the number of replacing operations of the bobbin can be reduced, thereby increasing workability. However, if a size of the bobbin case is increased according to the increase in the winding amount of the lower thread, since the length of the upper thread pulled by the thread take-up lever is limited, the length of the upper thread is not enough to wrap the bobbin case. In other words, since the loop of the upper thread having the short length cannot wrap the bobbin case BC, the upper thread is broken. The only answer to solve the problem is that a length of the thread take-up lever is increased. However, since a basic con- struction of the sewing machine, which is globally compatible, has to be changed, it is actually impossible.

[17] The upper thread is broken at an inflection portion 36 in which a maximum tensile force is applied to the upper thread while the loop of the upper thread becomes wider at both sides of the base 30 and the body 50 by the thread guide 26 of the hook body 20 (FIG. 8) and then comes off from the base 30 (FIG. 9), and in which a bottom surface 37 and an upright surface 35 are contacted with each other after a starting point of the track portion 32 formed at the base 30.

[18] As an alternative plan, as shown in FIG. 11, there has been proposed a bobbin case base 30'in which the inflection portion 36 is rounded and a bored portion 38 is formed by cutting away a part of the bottom surface 37 so as to minimize catching of the upper thread and a guide track 39 is also formed at the inflection portion 36 so as to avoid the catching of the upper thread.

[19] However, in order to increase the winding amount of the lower thread 4, the bottom surface 37 of the base 30 is inescapably extended to the outside so as to increase an ac- commodating space. Therefore, an opening of a bored portion 38 between the bottom surface 37 and the upright surface 35 is increased. As shown in FIG. 12, an outer cir- cumference of the first flange 43 of the bobbin 40 is exposed through the opening of the board portion 38.

[20] Furthermore, the more the lower thread is wound on the bobbin 40, the wider the first flange 43 and the second flange or the partition flange 37 is spread to the outside by tension of the lower thread itself.

[21] As described above, since the first flange 43 of the bobbin is exposed through the opening of the bored portion 38 formed at the bottom surface of the base 30, and is spread to the outside by the tensile force of the thread, the outer circumference of the first flange 43 of the bobbin 40 is apart from the upright surface 35 of the base 30. As a result, there is a problem that the upper thread is caught by the first flange 43 that is spread to the outside of the upright surface 35 of the base 30 at a high rotational speed while the loop of the upper thread comes off from the base 30 and is finally broken.

[22] Accordingly, although the upper thread can safely pass the inflection portion 36, since the upper thread is caught by the first flange 43 of the bobbin, it is limited to increase the winding amount of the lower thread.

[23] Thus, since the first flange 43 is irregularly rubbed with the bottom surface 37 of the base 30, there is a problem that the lower thread wound on the bobbin 40 is ir- regularly released whereby the lower thread is entangled or broken. Furthermore, when the bobbin is spun, the thread comes off to the outside of the first flange. And a distal end of the partition flange 47 that is spread to the outside may be collided with the needle.

[24] Meanwhile, the hook 25a of the gib 25 disposed at the hook body 20 functions to hold the upper thread at the final stage so that a tension of the upper thread that is passed as described above can be kept.

[25] As shown in FIG. 13, preferably, the upper thread 3 and the lower thread 4 are crossed at a center portion of objects 5a and 5b to be sewn. When the upper thread 3 and the lower thread 4 are crossed at the center portion of the objects, as shown in FIG.

14, stitches are aligned in a straight line. This result can be obtained only when each tension of the upper thread and the lower thread is coincident with each other.

[26] However, if the tension of the upper thread 3 is not kept, as shown in FIG. 15, the upper thread 3 is drooped downward. If the tension of the upper thread 3 is excessive, as shown in FIG. 16, the upper thread 3 gets loose upward and the lower thread 4 is fluttered roughly.

[27] As described above, the hook 25a of the gib 25 of the hook body 20 keeps the tension of the upper thread, and holds the thread passing the body 50 opposite to the base 30, and release the upper thread at a different point of time according to a thickness and a speed of the objects to be sewn.

[28] For example, if the objects are sewn at a high speed, the hook 25a has to have a long distance to hold the upper thread for longer time. If the objects are thin, the hook 25a also has to keep the upper thread for longer time.

[29] Accordingly, since the gib 25 of the hook body 20 for adjusting the tension may have a different construction according to the objects and the sewing speed, there is a problem that a user has to prepare so many kinds of hook bodies and replace the hook body in every sewing operation. Further, since the hook 25a of the gib 25 holds the upper thread at a lower side, the tension is leaned to one side, and the stitches are not aligned in the straight line, as shown in FIG. 17. Therefore, there is another problem that a sewing quality is lowered.

[30] DISCLOSURE OF THE INVENTION [31] Therefore, an object of the present invention is to provide a rotary shuttle device for a sewing machine, in which an inclined portion is formed at a first flange of a bobbin so as to allow a significant increase in a winding amount of lower thread and prevent a thread breakage and a thread tangle, and also in which a hook body is adapted to have a single model regardless of a sewing speed and a thickness of a sewing material so as to obtain a good sewing quality.

[32] Another object of the present invention is to provide a rotary shuttle device for a sewing machine, in which a replacement of the hook body is not needed regardless of the sewing speed and a thickness of a sewing material so as to obtain a good sewing quality, thereby remarkably reducing a cost of a component and workforce and labor for replacing the component [33] According to the present invention, a rotary shuttle device for a sewing machine, comprising a hook body disposed at a driving shaft; a bobbin case provided with a bobbin case base having a stud rod and accommodated in the hook body and a bobbin case body for holding a bobbin at an outside; and a bobbin formed with a winding shaft which is disposed in the bobbin case and on which lower thread is wound, a first flange formed at one end of the winding shaft so as to be contacted with a bottom surface of the bobbin case base and a second flange formed at the other end of the winding shaft, is characterized in that the bobbin has an inclined portion in which a part of the first flange is inclined toward a winding portion.

[34] Preferably, the first flange of the bobbin is formed with a flat bottom rubbed with a side of the bobbin case base and the inclined portion formed to be inclined toward the winding portion at an outer circumference thereof.

[35] Preferably, the bobbin comprises the first flange having the inclined portion, the winding shaft, the second flange, and a partition flange between the first flange and the second flange, wherein a portion between the first flange and the second flange is extended.

[36] Preferably, the partition flange has an inclined portion which is inclined toward the first flange at an outer circumference thereof.

[37] BRIEF DESCRIPTION OF DRAWINGS [38] FIG. 1 is an exploded perspective view of a conventional rotary shuttle device for a sewing machine; [39] FIG. 2 is a view showing a status that upper thread threaded through a needle is hooked on a hook body when the needle is moved down; [40] FIG. 3 is a view showing a moment that the upper thread is hooked by the hook body; [41] FIG. 4 is a side view of FIG. 3; [42] FIGs. 5 to 10 are views showing a sewing operation; [43] FIG. 11 is a perspective view of an example of a conventional bobbin case base; [44] FIG. 12 is a cross-sectional view showing a conventional mounting status of the hook body, the bobbin case base and the bobbin; [45] FIG. 13 is a cross-sectional view showing a preferable sewn status; [46] FIG. 14 is a plan view of FIG. 13; [47] FIG. 15 is a view showing a defective condition comparing with FIG. 13; [48] FIG. 16 is a view showing other defective condition comparing with FIG. 13; [49] FIG. 17 is a view showing a defective condition comparing with FIG. 14; [50] FIG. 18 is an exploded view of a rotary shuttle device for a sewing machine according to an embodiment of the present invention; [51] FIG. 19 is a cross-sectional view of FIG. 18; [52] FIG. 20 is a perspective view according to another embodiment of the present invention; [53] FIG. 21 is a cross-sectional view of FIG. 20; and [54] FIG. 22 is a view showing a mounting status according to the embodiment of the present invention.

[55] BEST MODE FOR CARRYING OUT THE INVENTION [56] The present invention will now be described in further detail by examples. It would be obvious to those skilled in the art that these examples are intended to be more concretely illustrative and the scope of the present invention as set forth in the appended claims is not limited to or by the examples.

[57] FIG. 18 is an exploded view of a rotary shuttle device for a sewing machine according to an embodiment of the present invention, and FIG. 19 is a cross-sectional view of FIG. 18. A rotary shuttle device 1 for a sewing machine according to an embodiment of the present invention comprises a hook body 25 disposed at a driving shaft 10; a bobbin case BC provided with a bobbin case base 30 having a stud rod 31 and accommodated in the hook body 20 and a bobbin case body 50 for holding a bobbin at an outside; and a bobbin 400 formed with a winding shaft which is disposed in the bobbin case BC and on which lower thread is wound, a first flange formed at one end of the winding shaft so as to be contacted with a bottom surface of the bobbin case base 30 and a second flange formed at the other end of the winding shaft. A part of the first flange 430 is inclined toward a winding portion so as to form an inclined portion 431.

[58] The first flange 430 of the bobbin 400 is formed with a flat bottom 433 rubbed with a side of the bobbin case base 30 and the inclined portion 431 formed to be inclined toward the winding portion at an outer circumference thereof.

[59] The first flange 430 having the inclined portion 431 can be applied to an expanded bobbin 401 in which a portion between the first flange 430 and the second flange 450 is formed to be extended and which has a partition flange 470 between the first flange 430 and the second flange 450 so as to divide the winding portion into two sections, and also applied to a basic bobbin 402 in which the first flange 430 and the second flange 450 are formed at both ends of the winding shaft 410, as shown in FIGs. 20 and 21.

[60] In the case of the expanded bobbin 401, it is preferred that the partition flange 470 has the inclined portion 471 which is inclined toward the first flange 430 at an outer circumference thereof (Referring to FIGs. 18 and 19).

[61] An operation status of the rotary shuttle device for a sewing machine according to the present invention will be described with reference to FIG. 22.

[62] According to the present invention, since the first flange 430 of the bobbin 400 is formed with the flat bottom 433 rubbed with the side of the bobbin case base 30 and the inclined portion 431 formed to be inclined toward the winding portion at an outer circumference thereof, even through the bottom surface 37 of the bobbin case base 30 is convexed so as to increase an inner space thereof, the outer circumference of the first flange 430 is not exposed through a bored portion 38 of the bobbin case base30.

Therefore, through a large quantity of lower thread is wound upon the bobbin 400 and tension of the thread is thus applied, a gap is not formed between an distal end of the first flange 430 and an upright surface 35 of the bobbin case base 30, whereby a loop of upper thread is not caught during a sewing operation and the loop of upper thread can climb over the inclined portion 431 so as to be facilely come off while maintaining tension of the upper thread 3.

[63] As described above, the loop of the upper thread can climb over the inclined portion 431 so as to be facilely come off while maintaining tension of the upper thread, thereby obtaining advantageous effects as follows: [64] First, since the first flange 430 is convexed to the outside due to the inclined portion 431, in other words the flat bottom 433 of the first flange 430 is widened, a length of the winding shaft 410 is extended as long as the flat bottom 433 is widened, thereby remarkably increasing a winding capacity of the bobbin.

[65] In the bobbin, if lmm of the length for the winding shaft is further extended, the winding capacity of thread is increased to 15-20%. Therefore, ifthe first flange 430 is convexed to the outside and the flat bottom 433 is thus widened, the winding capacity can be enormously increased.

[66] Secondly, since a surface area of the flat bottom 433 rubbed with the bottom surface 37 of the bobbin case base 30 is decreased due to the formation of the inclined portion 431, frictional resistance is reduced, and thus the lower thread is equally released.

Since the distal end of the first flange 430 is not exposed to the outside of the bobbin case base 30, it is prevented that the lower thread goes over to the outside of the first flange 430, and thus it is also prevented that the thread is broken or tangled even whenthe bobbin is spun [67] Thirdly, since the loop of the upper thread can smoothly go over the inclined portion 431 and also facilely come off from the bobbin case base, it is prevented that the thread is broken. Further, since the bobbin case body 50 is convexed to the outside so as to increase the inner space of the bobbin, it is possible to extend the length of the winding shaft 410 of the bobbin and also increase the lower thread winding capacity.

[68] On the other hand, the bobbin case body 50 may be also convexed to the outside so as to the inner space. Further, since a convexed portion 55 of the bobbin case body 50 functions to keep the tension of the upper thread until the loop of the upper thread comes off, the existing hook 25a for holding the upper thread is no longer needed.

Therefore, the gib 25 can be commonly used as a single model regardless of a sewing speed and a thickness of a sewing material (Referring to FIG. 22).

[69] Accordingly, since it is not necessary to prepare so many kinds of hook bodies including the gib which has various shapes according to the sewing speed and the thickness of the sewing material, the equipment for operating the sewing machine is simplified. In addition, since the tension is precisely kept, the sewing operation can be exactly performed so that the upper thread 3 and the lower thread 4 are placed at a center portion of the sewing material (referring to FIGs. 13 and 14), thereby obtaining a good sewing quality.

[70] Meanwhile, since the inclined portion 471 is also formed at the distal end of the partition flange 470, though the partition flange 470 is spread to the outside by tension of the wound thread, it is possible to minimize the risk of the collision of the needle 2, thereby improving the safety.

[71] While the present invention has been described in detail, it should be understood that various changes, substitutions and alterations could be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.

[72] INDUSTRIAL APPLICABILITY [73] As described above, the rotary shuttle device for a sewing machine according to the present invention has an inclined portion at a first flange of a bobbin, thereby increasing a winding amount of lower thread and preventing a thread breakage and a thread tangle. Further, the rotary shuttle device for a sewing machine according to the present invention uses a hook body having a single model regardless of a sewing speed and a thickness of a sewing material, thereby obtaining a good sewing quality.

[74] Furthermore, in the rotary shuttle device for a sewing machine according to the present invention, it is not necessary to replace of the hook body regardless of the sewing speed and the thickness of the sewing material, thereby remarkably reducing a cost of a component and workforce and labor for replacing the component.