Description

ROTARY SHUTTLE DEVICE FOR SEWING MACHINES WITH

UNDER THREAD GUARD

Technical Field

[1] The present invention relates, in general, to rotary shuttle devices for sewing machines and, more particularly, to a rotary shuttle device for sewing machines, in which an under thread guard protrudes from an end of the sidewall of a bobbin case base so as to guide an under thread and prevent the under thread from being hooked by a hook body, thus preventing the under thread from being hooked by a first hook of the hook body and preventing both abrupt cutting of the under thread and interruption of sewing work, thereby causing the sewing work to progress continuously and satisfactorily and increasing the productivity of sewing work. Background Art

[2] As shown in FIG. 1, a conventional sewing machine is provided with a rotary shuttle device 100 for the supply of under thread. The rotary shuttle device 100 comprises a hook body 20, which is mounted to a drive shaft 10, rotatably coupled to a drive unit, and is called an "outer hook" in the art, a bobbin case BC, received in the hook body 20, and a bobbin 40 with an under thread wound around the bobbin 40. The bobbin case BC comprises a bobbin case base 30, which is received in the hook body 20 and is called an "inner hook", and a bobbin case body 50 for holding the bobbin 40 at a location outside the bobbin case base 30.

[3] A stud 31 is axially provided at the center of the bottom of the bobbin case base 30 such that it is perpendicular to the bottom. The bobbin 40 is rotatably fitted over the stud 31.

[4] A track groove 21 is formed in the inner surface of the hook body 20, and a first hook 22 is formed in one end of the track groove 21. A cutout 23, having a gentle radius of curvature, is formed in the sidewall of the hook body 20 at a location near the first hook 22, such that the under thread can pass by the cutout 23 while being in contact therewith.

[5] Further, the bobbin case base 30 is provided around the sidewall thereof with a track rim 32, which is inserted into the track groove 21 in the hook body 20. The bobbin case base 30 is rotatably installed in the hook body 20. Further, a semicircular gib 25 is mounted to half of the outer circumferential part of the hook body 20 using a locking member, such as a locking bolt. Due to the gib 25, the bobbin case base 30 can be rotatably installed in and removed from the hook body 20. The gib 25 is provided with a second hook 25a, corresponding to the first hook 22 of the hook body 20. In

addition, an under thread guard 26 is detachably mounted to the remaining half of the outer circumferential part of the hook body 20 using a locking member, such as a locking bolt, such that the under thread guard 26 and the gib 25 are arranged in succession. The under thread guard 26 is provided with a third hook 26a, which corresponds to the second hook 25 a of the gib 25.

[6] At a location near the bobbin case BC comprising the bobbin case base 30 and the bobbin case body 50, a hook holder bracket 2 is installed in the body of the sewing machine and is inserted into a holding slot 33 in the bobbin case base 30, thus holding the bobbin case BC so as to prevent the bobbin case BC from moving. Further, a needle passing hole 34 is formed in the bobbin case base 30 at a location near the holding slot 33, and allows a needle to pass therethrough when the needle descends.

[7] The bobbin 40 comprises a winding shaft 41, around which the under thread is wound, and opposite flanges 43 and 45, formed in both ends of the winding shaft 41.

[8] The operation of the rotary shuttle device having the above-mentioned construction will be described hereinbelow.

[9] When the sewing machine is operated, the hook body 20 is rotated and, at the same time, both a needle and a thread take-up lever (not shown) for the upper thread execute respective vertical reciprocations. While the hook body 20 is rotated two times, the upper thread needle hooks and lifts the under thread once and pulls a predetermined length of under thread by a thread take-up action, thus preparing for the next under thread hooking and lifting action.

[10] FIG. 2 is a view illustrating a needle in a state in which the needle has been lowered to be hooked by the hook body. FIG. 3 is a view illustrating the moment that the hook body hooks the upper thread. FIG. 4 is a side view of FIG. 3.

[11] Further, FIG. 5 through FIG. 10 are views sequentially illustrating sewing work, in which the drawings accompanied by the characters a, b, c, d, e and f show the rotary shuttle device in front views, and the drawings accompanied by the apostrophized characters a', b', c', d', e' and f show the rotary shuttle device in perspective views with the hook body 20 inverted such that the bottom thereof faces upwards for easy comprehension of the construction thereof.

[12] When the sewing machine is operated, the needle 2, through which the upper thread

3 has been run, is lowered and, at the same time, the hook body 20 is rotated in response to the lowering action of the needle 2, so that the first hook 22 of the hook body 20 hooks and pulls the upper thread downwards (see FIG. 2 through FIG. 6). The above-mentioned action of the first hook 22 of the hook body 20 is realized using a notch 2a, which is formed in one side surface of the needle 2 such that the first hook 22 can hook and pull the upper thread 3, running through the needle 2, downwards. In the above state, if the needle 2 and the first hook 22 are spaced excessively far apart from

each other, the first hook 22 may fail to hook the upper thread 3, thus skipping over one or more stitches on the sewing line or failing to executing the sewing. On the contrary, if the needle 2 and the first hook 22 are excessively close to each other, the needle 2 may collide with the first hook 22 and may break.

[13] As described above, the upper thread 3, which has been hooked and lowered by the first hook 22 of the hook body 20, is guided by the thread guard 26 of the hook body 20 and forms a noose to surround and hook the bobbin case BC, comprising the bobbin case base 30 and the bobbin case body 50, thus hooking and lifting the under thread 4 (see FIG. 7 through FIG. 10). The formation of the noose formed by the upper thread 3, which surrounds the bobbin case BC, is realized by the thread take-up lever, which has pulled a predetermined length of upper thread in a previous stroke.

[14] The length of the upper thread, which has been pulled by the thread take-up lever while the lever reciprocates once, is equal to the length of the thread which is required to surround the bobbin case BC during one rotation of the hook body 20. If the volume of the hook body 20, which has a close relationship with the volume of the under thread, is increased, the length of the upper thread pulled by the thread take-up lever becomes short, so that the upper thread may be cut. Conversely, if the length of the upper thread pulled by the thread take-up lever exceeds a predetermined length so that surplus thread is present, the under thread cannot be tensioned, thus causing a loop phenomenon or a towel phenomenon, in which the under thread becomes loose on the sewing line and forms a fine nap thereon.

[15] At the initial stage in sewing work, a predetermined sufficient length of under thread is released from the bobbin case and droops outside the hook body, thus being hooked by the noose of the upper thread in a later stage.

[16] However, when the under thread 4 droops as described above, the under thread may be hooked between the first hook 22 of the hook body 20 and the third hook 26a of the under thread guard 26, as shown in FIG. 11. When the hook body 20 is rotated in the above state, the under thread 4 is inserted into and caught by the gap between the hook body 20 and the bobbin case base 30, and thus the under thread may be cut during the first rotation of the hook body 20, resulting in the interruption of sewing work and reducing the productivity of the sewing work. Disclosure of Invention Technical Problem

[17] Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and is intended to provide a rotary shuttle device for sewing machines, in which an under thread guard for guiding an under thread so as to prevent the under thread from being hooked by a hook body protrudes from one end

of the sidewall of a bobbin case base, thus preventing the under thread from being hooked by a first hook of the hook body and preventing both abrupt cutting of the under thread and interruption of sewing work, thereby enabling the sewing work to progress continuously and satisfactorily and increasing the productivity of sewing work.

Technical Solution

[18] In an aspect, the present invention provides a rotary shuttle device for sewing machines, comprising: a hook body mounted to a drive shaft and provided with a first hook for hooking an upper thread; a bobbin case comprising a bobbin case base received in the hook body and a bobbin case body for holding a bobbin at a location outside the bobbin case base; and the bobbin installed in the bobbin case and having an under thread wound therearound,

[19] wherein the bobbin case base comprises: a stud axially provided at a center of a bottom of the bobbin case base, a sidewall comprising a first section, defined between a base surface and a track rim, and a second section, defined at a location behind the first section and partially open to have opposite ends; a flange part formed around a top end of the second section of the sidewall such that the flange part protrudes outwards in a radial direction; a holding slot formed on the flange part at a location near the first end of the second section, thus holding the bobbin case base in a body of a sewing machine; and a needle passing hole formed in the bobbin case base at a location near the holding slot and allowing a needle to pass therethrough when the needle descends,

[20] wherein the bobbin case base further comprises an under thread guard, which protrudes from the first end of the sidewall of the bobbin case base and functions to prevent the under thread from being hooked by the hook body.

Advantageous Effects

[21] As described above, the rotary shuttle device for sewing machines according to the present invention is provided with an under thread guard, which protrudes from one end of the sidewall of a bobbin case base so as to guide an under thread and prevent the under thread from being hooked by a hook body, thus preventing the under thread from being hooked by a first hook of the hook body and preventing both the abrupt cutting of the under thread and the interruption of sewing work, thereby causing the sewing work to progress continuously and satisfactorily and increasing the productivity of sewing work. Brief Description of the Drawings

[22] FIG. 1 is an exploded perspective view illustrating a conventional rotary shuttle device for sewing machines;

[23] FIG. 2 is a view illustrating a needle in a state in which the needle has been lowered

to be hooked by a hook body;

[24] FIG. 3 is a view illustrating the moment the hook body hooks an upper thread;

[25] FIG. 4 is a side view of FIG. 3;

[26] FIG. 5 through FIG. 10 are views sequentially illustrating sewing work;

[27] FIG. 11 is a perspective view illustrating the conventional rotary shuttle device in an assembled state; [28] FIG. 12 is an exploded perspective view illustrating a rotary shuttle device for sewing machines according to an embodiment of the present invention; [29] FIG. 13 is a front view of a bobbin case base shown in FIG. 12;

[30] FIG. 14 is a top plan view of the bobbin case base of FIG. 13;

[31] FIG. 15 is a perspective view illustrating the rotary shuttle device of FIG. 12 in an assembled state; [32] FIG. 16 is a sectional view illustrating a part of the rotary shuttle body of FIG. 15 in detail; and [33] FIG. 17 is a perspective view illustrating a rotary shuttle device for sewing machines according to another embodiment of the present invention. [34] *Description of the elements in the drawings*

[35] 1: rotary shuttle device for sewing machines with under thread guard according to the present invention

[36] 2: needle 3: upper thread 4: under thread

[37] 10: drive shaft 20: hook body 22: first hook

[38] 30: conventional bobbin case base

[39] 300: bobbin case base according to the present invention

[40] 30a: sidewall 31 : stud 32: track rim

[41] 33: holding slot 34: needle passing hole

[42] 35: under thread guard

[43] 35a: shoulder part 38: flange part 40: bobbin

[44] 50: bobbin case body

[45] 100: conventional rotary shuttle device

Mode for the Invention [46] Hereinbelow, preferred embodiments of the rotary shuttle device for sewing machines according to the present invention will be described in detail with reference to the accompanying drawings. [47] FIG. 12 is an exploded perspective view illustrating a rotary shuttle device for sewing machines according to an embodiment of the present invention. FIG. 13 is a front view of the bobbin case base shown in FIG. 12. FIG. 14 is a top plan view of the bobbin case base of FIG. 13. FIG. 15 is a perspective view illustrating the rotary

shuttle device of FIG. 12 in an assembled state. FIG. 16 is a sectional view illustrating part of the rotary shuttle body of FIG. 15 in detail.

[48] As shown in FIG. 12 through FIG. 16, the rotary shuttle device 1 for sewing machines with an under thread guard according to a first embodiment of the present invention comprises a hook body 20, which is mounted to a drive shaft 10 and is provided with a first hook 22 for hooking an upper thread, a bobbin case BC comprising a bobbin case base 300, which is received in the hook body 20, and a bobbin case body 50 for holding a bobbin 40 at a location outside the bobbin case base. The bobbin 40 is installed in the bobbin case BC and has an under thread wound therearound. A stud 31 is axially provided at the center of the bottom of the bobbin case base 300 such that it is perpendicular to the bottom. Further, the bobbin case base 300 has a sidewall 30a, which comprises a first section 36, defined between a base surface and a track rim 32, and a second section 37, defined at a location behind the first section and partially open to have opposite ends 37a and 37b. A flange part 38 is formed around the top end of the second section 37 of the sidewall such that the flange part 38 protrudes outwards in a radial direction. To hold the bobbin case base 300 in the body of a sewing machine, the flange part 38 is provided with a holding slot 33 at a location near the first end 37a of the second section 37. Further, a needle passing hole 34 is formed in the bobbin case base 300 at a location near the holding slot 33, and allows a needle to pass therethrough when the needle descends.

[49] Further, according to the present invention, an under thread guard 35 protrudes from the first end 37a of the sidewall 30a of the bobbin case base 300 and functions to prevent an under thread from being hooked by the hook body 20.

[50] Here, it is preferred that the under thread guard 35 be formed on an extension line of the flange part 38, which is formed around the top end of the second section 37 of the sidewall 30a, and that a shoulder part 35a be formed on the end of the under thread guard 35 such that the shoulder part 35a protrudes outwards from the first hook 22 of the hook body 20.

[51] In other words, the under thread guard 35 covers the first hook 22 at a drooping path of the released under thread 4 such that the under thread 4 can be prevented from being hooked by the first hook 22 of the hook body 20.

[52] Here, it is preferred that the shoulder part 35a not protrude from the end of the under thread guard 35 at any position, but that the protrusion of the shoulder part 35a be gradually reduced such that the outside end of the shoulder part 35a is located inside the bobbin case BC.

[53] Further, the under thread guard 35 has a curved shape, which is formed with a predetermined width from the first end 37a of the sidewall 30a in a radial direction of the sidewall 30a such that the under thread guard 35 does not interfere with the rotation of

the hook body 20.

[54] Further, the shoulder part 35a of the under thread guard 35 is formed on an extension line with a degree θ of inclination defined by the end 39 of the sidewall 30a of the bobbin case base 300 extending from the holding slot 33 toward the opposite ends 37a and 37b. In other words, the height of the shoulder part 35a is gradually reduced.

[55] Here, the under thread guard 35 may be integrally formed with the bobbin case base

300.

[56] Alternatively, the under thread guard 35 may be produced separately from the bobbin case base 300 prior to being assembled with the bobbin case base 300, as shown in FIG. 17.

[57] The operation of the rotary shuttle device 1 for sewing machines with the under thread guard according to the present invention will be described hereinbelow.

[58] In the present invention, the under thread guard 35 for guiding the under thread to the outside of the hook body 20 protrudes from the first end 37a of the sidewall 30a of the bobbin case base 300, thus preventing the under thread from being hooked by the first hook 22 of the hook body 20.

[59] Described in detail, the shoulder part 35a of the under thread guard 35 protrudes outwards such that it is located outside the first hook 22 of the hook body 20 in a radial direction, thus covering the first hook 22 such that the first hook 22 can get out of the drooping path of the under thread 4 released from the bobbin case BC.

[60] In other words, the under thread guard 35, which functions as a plate cover, is located at a position above the first hook 22, which may function as obstruction in the drooping path of the under thread 4 released from the bobbin case BC. Thus, the under thread guard 35 allows the under thread 4 to avoid the first hook 22 and prevents interference between the under thread 4 and the first hook 22.

[61] Therefore, the under thread guard 35 of the present invention prevents the under thread 4 from being hooked by the first hook 22 or from being inserted into a gap between the hook body 20 and the bobbin case base 300 regardless of the drooping length of the under thread before sewing work commences, thus preventing both abrupt cutting of the under thread and interruption of sewing work, thereby allowing the sewing work to progress continuously and satisfactorily.

[62] In the above description, the embodiments of the present invention have been disclosed for illustrative purposes with reference to the accompanying drawings. Here, the technical terms and words used in the specification and claims must not be interpreted according to limited definitions thereof, such as ordinary or dictionary meanings, but must be understood to represent meanings and concepts corresponding to the technical scope and spirit of the invention. Thus, those skilled in the art will

appreciate that the construction of the embodiments and drawings of the invention has been disclosed as that of preferred embodiments, and thus various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. Industrial Applicability

[63] As described above, the rotary shuttle device for sewing machines according to the present invention is provided with an under thread guard, which protrudes from an end of the sidewall of a bobbin case base so as to guide an under thread and prevent the under thread from being hooked by a hook body, thus preventing the under thread from being hooked by a first hook of the hook body and preventing both abrupt cutting of the under thread and interruption of sewing work, thereby allowing the sewing work to progress continuously and satisfactorily and increasing the productivity of the sewing work.