[ 1 ] A UNDER THREAD SUPPLY DEVICE OF SEWING MACHINE

[2] TECHNICAL FIELD

[3] The present invention relates to a under thread supply device of a sewing machine, in which a position of withdrawing under thread can be fixedly and stably maintained, thereby improving the sewing quality and workability and, at the same time, reducing the number of components and fabricating processes so that a fabricating cost can be reduced.

[4] BACKGROUND ART

[5] Generally, in the sewing machine, as shown in FIG. 1, there is provided a under thread supply device for supplying the lower thread. The under thread supply device comprises a hook body 120 disposed at a driving shaft 110 which is rotatably connected to a driving apparatus, a bobbin case BC accommodated in the hook body 120 and a bobbin 140 on which the under thread is wound. The bobbin case BC comprises a bobbin case base 130 accommodated in the hook body 120 and a bobbin case body 50 for receiving the bobbin 140 from an outside of the bobbin 140.

[6] At a bottom of the bobbin case base 130, there is upright disposed a stud 131. The bobbin 40 is rotatably disposed at the stud 131. At the bobbin case body 150, there is formed a latch 151 for holding the 140 when being engaged with or released from the stud 131 formed in the bobbin case base 130.

[7] Now, an operation of the under thread supply device as described above will be described below. The hook body 20 is rotated by rotation of the driving shaft 110. The under thread is released from the bobbin while hooking upper thread and forming a loop for enclosing the bobbin case BC, and withdrawn through a under thread withdrawing opening 154. Then, the under thread is hooked up by a loop of the upper thread, thereby performing the sewing operation.

[8] In the sewing operation, firstly, the upper thread can have to smoothly hook up the under thread, and the tension of the hooked under thread has to be balanced with that of the upper thread. If a position of withdrawing the under thread is deviated from a preset position, it is difficult that the loop of the upper thread hooks up the under thread. Therefore, the thread is broken or the thread is dangled down and fluttered roughly, thereby obstructing the sewing operation.

[9] Furthermore, in the sewing machine, there is provided a thread cutting device for automatically cutting the under thread when the sewing operation is completed. Thus, it saves trouble of manually cutting the under thread in every sewing section.

[10] In the sewing operation using the thread cutting device as described above, in the case of a general sewing machine in which a table is immovable, since a position of

withdrawing the under thread is fixed, there is no any problem. However, in the case of an embroidery sewing machine in which the table is movable, since the position of withdrawing the under thread in the next operation after cutting the under thread is not fixed, a under thread guiding means is required.

[11] In a conventional bobbin case body 150 provided with the under thread guiding means, as shown in FIG. 1, a coil spring-shaped guide coil 155 is fixedly provided at the bobbin case body 150 in a direction that a needle comes down, so that the under thread is passed through the guide coil 155, thereby fixing the position of withdrawing the under thread.

[12] In addition, the under thread has to be steadily held at the moment when it is cut.

Therefore, peaks in the form of pincers are disposed at a body of the sewing machine, and comes down at both sides of the guide coil 155 by an action of a lever.

[13] However, since the guide coil 155 formed of the thin coil as described above is deformed by the tension of the under thread, the position of withdrawing the under thread is leaned to either of the right or left side. Therefore, there are some problems that it is hard that the upper thread hooks up the under thread and it also causes one inconvenience in the embroidery sewing operation due to the thread breakage and the tension unbalance.

[14] In addition, since one thin end of the guide coil 155 as a separate member is welded to the bobbin case body 150, the welded portion between the guide coil 155 and the bobbin case body 150 is very weak. Further, the guide coil 155 has to be positioned at a center portion of the peaks so as to prevent interference with the peaks. However, due to the deformation of the guide coil 155, the guide coil 155 is collided with the peaks due to the deformation of the guide coil 155, so that the guide coil is often cut away.

[15] Further, as described above, the guide coil 155 has to be placed at an exact position of the bobbin case body. However, since a separate member is welded thereto, there are also some problems that the number of components is increased, and at the same time, a welding operation required to pay close attention is accompanied, thereby increasing a fabricating cost.

[16] DISCLOSURE OF THE INVENTION

[17] Therefore, an object of the present invention is to provide a under thread supply device of a sewing machine, in which deformation of a under thread guide provided at a latch of a bobbin case body is prevented, so that a position of withdrawing under thread can be fixedly and stably maintained, thereby improving sewing quality and workability and, at the same time, reducing the number of components and fabricating processes so that a fabricating cost can be reduced.

[18] According to the present invention, a under thread supply device of a sewing

machine, comprising a bobbin case body 50 provided with a latch 51, is characterized in that the latch 51 of the bobbin case body 50 is integrally formed with a under thread guide 15a at a side thereof.

[19] BRIEF DESCRIPTION OF DRAWINGS

[20] FIG. 1 is an exploded perspective view of a part of a conventional under thread supply device of a sewing machine; and

[21] FIG. 2 is an exploded perspective view of a part of a under thread supply device of a sewing machine according to the present invention.

[22] BEST MODE FOR CARRYING OUT THE INVENTION

[23] 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.

[24] FIG. 2 is an exploded perspective view of a part of a under thread supply device of a sewing machine according to an embodiment of the present invention.

[25] As shown in FIG. 2, a under thread supply device of a sewing machine according to an embodiment of the present invention comprises a hook body 20 disposed at a driving shaft 10; a bobbin case base 30 having a stud 31 and accommodated in the hook body 20; a bobbin case body 50 receiving a bobbin 40 at an outside of the bobbin and having a latch 51 for holding the bobbin when the bobbin is mounted onto or separated from the stud 31 ; and a bobbin 40 disposed in the bobbin case 30 and 50. The latch 51 of the bobbin case body 50 is integrally formed with a under thread guide 51a at one side thereof.

[26] The under thread guide 5 Ia of the latch 51 is protruded in a direction that a needle comes down. Preferably, the under thread guide 51a is formed into a link-shaped plate having a curved admission passage 51aa.

[27] The bobbin case body 50 is formed with a groove 55 formed in the latch 51 so as to receive the under thread guide 51a. Preferably, the under thread guide 51a is bent to an inside so as not to deviate from an outer line of the bobbin case body 50, so that the under thread guide 51a is not interfered with the driving of the bobbin case body.

[28] Besides the above-mentioned shape, the under thread guide 51a may have various shapes.

[29] According to the present invention as described above, the under thread guide 51a is integrally formed at the latch 51 so as to be prevent the deformation of the under thread guide 51a. Therefore, the under thread can be always withdrawn at a fixed portion so that the upper thread can facilely hooks up the under thread. Thus, the tension balance between the upper thread and the under thread can be stably maintained, thereby improving the quality of embroidery sewing operation and fa-

cilitating the sewing operation.

[30] In addition, since the under thread guide 51a is integrally formed at the latch 51, it is prevented that under thread guide 51a is deformed. Further, since shaking is not occurred at the bobbin case body 50, there is no need of apprehension that the under thread guide 51a is damaged or cut away. Furthermore, since the position of the under thread guide 51a is deviated from that of the peaks, there is no need of apprehension of colliding with the peaks.

[31] Moreover, since the under thread guide 51a is integrally formed into the plate shape at the latch 51, it is unnecessary to provide separate components or separate assembling or bonding processes, thereby considerably improving productivity.

[32] 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.

[33] INDUSTRIAL APPLICABILITY

[34] According to the under thread supply device of a sewing machine as described above, since it is prevented that the under thread guide provided at the latch of the bobbin case body is deformed, the position of withdrawing under thread can be fixedly and stably maintained, thereby improving the sewing quality and workability and, at the same time, reducing the number of components and fabricating processes so that a fabricating cost can be reduced.