Patent Application
20100126398
The present invention relates to a bobbin thread feeder of sewing machine comprising a horizontal rotary hook that removably contains a lower thread bobbin, wherein a lower thread can be easily set during a sewing operation.
As sewing machines for household use, a model comprising a horizontal rotary hook in which a lower thread bobbin does not have to be contained in a bobbin case when being attached is becoming a mainstream instead of the one comprising a vertical rotary hook. In the case of sewing machines comprising a horizontal rotary hook, the lower thread bobbin need only to be set through an opening above the horizontal rotary hook into a rotary hook, and thus a bobbin thread feeder is provided so that a lower thread can be reliably fed.
For example, in Patent Document 1, a bobbin thread feeder is consisted such that a containing portion of a rotary hook in the shape of a cylindrical container is positioned below an opening for containing a lower thread bobbin provided at a needle plate. The lower thread bobbin is contained when a user directly sets the lower thread bobbin from above through the opening for containing the lower thread bobbin into the rotary hook. Accordingly, the lower thread bobbin does not have to be contained in a bobbin case when being set into the rotary hook as in the case of using a vertical rotary hook, and thus an operation that sets the lower thread bobbin can be easily performed.
The bobbin thread feeder comprises a tension generating portion in order to impart a resistance to a lower thread being pulled out which is guided from the lower thread bobbin. The tension generating portion is attached to a recessed portion formed along part of the inner circumferential face of the containing portion of the rotary hook, in a state where a thread tension plate and a thread tension spring are overlapped. The user sets the lower thread bobbin as described above, and then performs an operation to put a lower thread pulled out of the lower thread bobbin through the tension generating portion. In the case where the sewing machine is operated in a state where the lower thread is not properly put through the tension generating portion, the feeding amount of the lower thread becomes excessive as the tension of the lower thread decreases, the balance with the upper thread is lost, and thus the sewing operation cannot be performed well.
Thus, in Patent Document 1, a plate-shaped guide member disposed substantially in the horizontal direction above the tension generating portion of the rotary hook is provided so that a lower thread pulled out of the lower thread bobbin is guided to the tension generating portion. When the lower thread pulled out is moved so as to be guided by the guide member provided above the tension generating portion, the lower thread is reliably guided to between the thread tension plate and the thread tension spring and to the tension generating portion. Accordingly, the user can set a lower thread by a simple operation that guides the lower thread pulled out of the lower thread bobbin with the guide member.
Furthermore, in Patent Document 2, the front edge portion and the side edge portion of a needle plate are used as slits that guide a lower thread, and a connection slit that connects an opening for containing a lower thread bobbin and the front edge portion of the needle plate is formed in the front portion of the needle plate. When the user winds the lower thread from the connection slit to the front edge portion and the side edge portion of the needle plate, the lower thread is guided to between the thread tension plate and the thread tension spring and to the tension generating portion. Accordingly, the user can set a lower thread by a simple operation that guides the lower thread pulled out of the lower thread bobbin along the circumferential edge of the needle plate.
However, in Patent Document 1, there is a problem in that the structure of the bobbin thread feeder becomes complex because a guide member has to be additionally comprised only in order to guide a lower thread. Furthermore, in Patent Document 2, although a guide member does not have to be additionally provided, the needle plate has to be processed into an appropriate shape according to the shape and the position of the lower thread bobbin. Accordingly, in both cases, it is difficult to reduce the production costs. A simpler structure is required for sewing machines for household use, which are strongly required to be competitive in price.
The present invention was made in view of these circumstances, and it is an object thereof to provide a bobbin thread feeder of sewing machine that can reliably feed a lower thread at a proper tension, and that has a simple structure.
In order to achieve the above-described object, a first aspect of the present invention is directed to a bobbin thread feeder of sewing machine, in which a lower thread bobbin can be removably contained through an opening for containing the lower thread bobbin in a rotary hook of a horizontal rotary hook provided in a sewing machine frame, and in which a tension generating portion is provided for imparting a resistance to a lower thread being pulled out while passing and being guided between a thread tension plate and a thread tension spring, which are attached while overlapping along the inner circumference of the rotary hook, wherein a needle plate with an opening for taking the lower thread bobbin in and out is provided above the rotary hook, the needle plate comprises a guiding slit for guiding the lower thread, and the guiding slit is formed substantially linearly in the extending direction of the overlapping portion of the thread tension plate and the thread tension spring.
According to the first aspect of the present invention, a lower thread bobbin can be removably contained through an opening for containing the lower thread bobbin in a rotary hook of a horizontal rotary hook provided in a sewing machine frame. A thread tension plate and a thread tension spring are attached while overlapping along the inner circumference of the rotary hook, and function as a tension generating portion that imparts a resistance to a lower thread being pulled out while passing and being guided between the thread tension plate and the thread tension spring. A needle plate with an opening for taking the lower thread bobbin in and out is provided above the rotary hook. A guiding slit for guiding the lower thread is formed on the needle plate. The guiding slit is formed substantially linearly in the extending direction of the overlapping portion of the thread tension plate and the thread tension spring. When a user moves the lower thread along the guiding slit on the upper face side of the rotary hook that contains the lower thread bobbin, the lower thread can be guided to the overlapping portion of the thread tension plate and the thread tension spring, and an appropriate tension is imparted to the lower thread. Accordingly, it is possible to provide a bobbin thread feeder that does not impair the function of feeding the lower thread by imparting an appropriate tension thereto even if a guide member is not additionally provided, only by a simple production process that forms a substantially linear slit on the needle plate. Thus, production costs can be reduced.
Furthermore, a second aspect of the present invention is directed to the bobbin thread feeder of sewing machine according to the first aspect, wherein the needle plate comprises a thread-cutting portion for cutting the lower thread at a predetermined position where the length of the lower thread pulled out of the lower thread bobbin is longer than the length to the end of the guiding slit.
According to the second aspect of the present invention, the bobbin thread feeder comprises a thread-cutting portion for cutting the lower thread at a predetermined position of the needle plate such that the length of the lower thread pulled out of the lower thread bobbin is longer than the length to the end of the guiding slit. In the case where the length of the lower thread pulled out of the lower thread bobbin is too long, the lower thread pulled out with a blade point of an outer rotary hook and the upper thread may be intricately intertwined with each other. Furthermore, in the case where the length of the lower thread pulled out is too short, the blade point of the outer rotary hook may fail to catch the lower thread. Thus, when the lower thread can be reliably cut into an appropriate length, the user can easily set the lower thread.
According to the present invention, when the user moves the lower thread along the guiding slit on the upper face side of the rotary hook that contains the lower thread bobbin, the lower thread can be guided to the overlapping portion of the thread tension plate and the thread tension spring, and an appropriate tension is imparted to the lower thread. Accordingly, it is possible to provide a bobbin thread feeder of sewing machine that does not impair the function of feeding the lower thread by imparting an appropriate tension thereto even if a guide member is not additionally provided, only by a simple production process that forms a substantially linear guiding slit on the needle plate. Thus, production costs can be reduced because the number of parts is not increased.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, “front”, “rear”, “left” and “right” refer to the front, rear, left and right directions viewed by an operator operating a sewing machine.
On a portion that opposes the needle bar 15 and in which the sewing operation is performed, a needle plate 16 made of metal is provided.
The rotary hook 20 is provided with a tension generating portion 22. The tension generating portion 22 is attached with screws 25 and 26 or the like to an arc-shaped recessed portion 20d formed on part of the inner circumferential face of the containing portion 20a of the rotary hook 20, in a state where a thread tension plate 23 and a thread tension spring 24 are overlapped. The thread tension plate 23 and the thread tension spring 24 are arc in shape respectively along the recessed portion 20d in the same way, and a overlapping portion of the thread tension plate 23 and the thread tension spring 24 is set into the arc-shaped recessed portion 20d on the inner circumferential face of the containing portion 20a of the rotary hook 20.
The thread tension spring 24 is provided with a step portion 24a at the right end portion. The thread tension plate 23 and the thread tension spring 24 have a slight gap therebetween at substantially the central portion (a portion near the leading end of the slit 23b), and are substantially in close contact with each other at the left end portion (a portion near the hole 23a).
With this configuration, the lower thread pulled out of the lower thread bobbin 21 is guided along the slit 23b to the hole 23a. Accordingly, a resistance is imparted to the lower thread by the power of the thread tension plate 23 and the thread tension spring 24 pressing the lower thread therebetween, and the lower thread is fed in a state where an appropriate tension is imparted thereto.
In this embodiment, as shown in
More specifically, the guiding slit 27 is provided in the extending direction of the thread tension plate 23 and the thread tension spring 24 provided in the shape of arc on the inner circumferential face of the rotary hook 20 toward the main unit. Thus, the lower thread is passed between the thread tension plate 23 and the thread tension spring 24 and an appropriate tension is imparted to the lower thread when the user simply guides the lower thread along the guiding slit 27, without being conscious of guiding the lower thread to the groove portion 23c above the thread tension plate 23.
Furthermore, the needle plate 16 is provided with a thread-cutting portion 28. The thread-cutting portion 28 is configured with a closed-bottom groove 28a that is formed from the end of the guiding slit 27 along the outer edge of the needle plate 16, and a chamfering portion for a cutter 28c that guides a lower thread to the cutter 28b at a position where a sufficient length of the lower thread can be secured.
In the case where a sewing machine comprising the bobbin thread feeder configured as described above is used, the user first removes the cover 18 of the sewing table 12, and fits and sets the lower thread bobbin 21 into the containing portion 20a of the rotary hook 20. Then, the lower thread is pulled out of the lower thread bobbin 21, and caught on the slit 23b of the thread tension plate 23 first.
Next, the lower thread is rotated clockwise in a state where the lower thread is caught on the slit 23b, and guided toward the guiding slit 27 of the needle plate 16. When the lower thread is guided along the direction of the guiding slit 27, the lower thread caught on the slit 23b is lowered along the slit 23b, and guided to the hole 23a.
When the lower thread is guided to the hole 23a, the lower thread is brought into a state where an appropriate tension is imparted by the power pressed between the thread tension plate 23 and the thread tension spring 24. The user pulls out the lower thread along the guiding slit 27 in a state where a tension is imparted to the lower thread.
At the end portion of the guiding slit 27, the lower thread is guided to the closed-bottom groove 28a of the needle plate 16, and thus, the lower thread is guided from the end portion of the guiding slit 27 to the cutter 28b, along the closed-bottom groove 28a formed along the outer edge of the needle plate 16. When the lower thread penetrates in the chamfering portion for the cutter 28c, the lower thread is cut with the cutter 28b.
In this state, the user vertically moves the needle bar 15 with a drive mechanism (not shown). When the needle bar 15 is vertically moved, the outer rotary hook 29 of the horizontal rotary hook 30 rotates horizontally, and the upper thread is intertwined with the lower thread caught on the blade point, and pulled upward out of the needle hole 16a of the needle plate 16. In this state, the lower thread is pulled out of the hole 23a of the thread tension plate 23 of the rotary hook 20 through the groove portion 23c to the needle hole 16a, and thus, the user does not have to be conscious of guiding the lower thread to the groove portion 23c. When the upper thread and the lower thread pulled out are untwined, it is ready for sewing.
In this embodiment, the length of the lower thread pulled out can be kept substantially constant. Accordingly, there is no possibility that the lower thread pulled out at the blade point of the outer rotary hook 29 is intricately intertwined with the upper thread, for example, as in the case where the lower thread pulled out of the lower thread bobbin 21 is too long. Furthermore, there is no possibility that the blade point of the outer rotary hook 29 fails to catch the lower thread, for example, as in the case where the pulled out lower thread is too short, and thus, the user can reliably prepare for sewing.
Thus, according to this embodiment, the lower thread is guided between the thread tension plate 23 and the thread tension spring 24 to pass through the tension generating portion 22 only by the operation in which the lower thread pulled out of the lower thread bobbin 21 is rotated clockwise in a state where the lower thread is caught on the slit 23b on the upper face side of the rotary hook 20 and moved along the guiding slit 27 of the needle plate 16. Accordingly, without additionally providing an arched guide member or the like, for example, the lower thread can be reliably set. Furthermore, the guiding slit 27 is substantially linear, and thus, the minimum working process will do. Accordingly, production costs can be reduced.
Moreover, in this embodiment, the needle plate 16 is provided with the thread-cutting portion 28, and thus, the length of the lower thread pulled out of the lower thread bobbin 21 can be substantially constant in length. Accordingly, harmful effect of the pullout length can be prevented in advance.
It should be appreciated that the present invention can be worked with various modifications made to the above-described embodiment without departing from the gist of the invention, for example, mainor change in the configuration of the tension generating portion 22, change in the shape of the thread tension plate 23, change in the position to attach the thread-cutting portion 28, or the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-141305 | May 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/056486 | 4/1/2008 | WO | 00 | 11/4/2009 |
