Patent Publication Number: US-2010126398-A1

Title: Bobbin thread feeder of sewing machine

Description:
TECHNICAL FIELD 
     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. 
     BACKGROUND ART 
     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. 
     Patent Document 1: JP H10-146489A 
     Patent Document 2: JP 2005-312733A 
     DISCLOSURE OF INVENTION 
     Problem to be Solved by the Invention 
     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. 
     Means for Solving Problem 
     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. 
     EFFECT OF THE INVENTION 
     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. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing the appearance of a sewing machine according to an embodiment of the present invention. 
         FIG. 2  is a plan view of a needle plate according to the embodiment of the present invention. 
         FIG. 3  is a plan view showing the configuration of a bobbin thread feeder according to the embodiment of the present invention. 
         FIG. 4  is a perspective view showing the configuration of an rotary hook according to the embodiment of the present invention. 
         FIG. 5  is a front view of a thread tension plate according to the embodiment of the present invention. 
     
    
    
     DESCRIPTION OF NUMERALS 
     
         
           11  Sewing machine frame 
           16  Needle plate 
           17  Opening for containing a lower thread bobbin 
           20  Rotary hook 
           21  Lower thread bobbin 
           22  Tension generating portion 
           23  Thread tension plate 
           24  Thread tension spring 
           27  Guiding slit 
           28  Thread-cutting portion 
           29  Outer rotary hook 
           30  Horizontal rotary hook 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     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.  FIG. 1  is a perspective view showing the appearance of a sewing machine according to an embodiment of the present invention. As shown in  FIG. 1 , the sewing machine according to the embodiment comprises a sewing table  12  configured as part of a sewing machine frame  11 , and an arm portion  13  integrated with the sewing machine frame  11  and provided above the sewing table  12 . A needle bar  15  to which a sewing needle  14  is fixed is provided at the lower front portion of the arm portion  13 , and a sewing operation is performed when a well known drive mechanism (not shown) vertically moves the needle bar  15 . 
     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.  FIG. 2  is a plan view of the needle plate  16  according to the embodiment of the present invention. A needle hole  16   a  through which the sewing needle  14  passes is formed on the needle plate  16 , and an opening for containing the lower thread bobbin  17  which opens in a rectangular shape is formed in front of the needle hole  16   a.  In ordinary use, a transparent cover  18  ( FIG. 1 ) is placed on the opening for containing the lower thread bobbin  17 . Below the needle plate  16  in the sewing machine frame  11 , a feed dog mechanism (not shown) for feeding fabric that is driven according to the vertical movement of the needle bar  15  is provided, and a bobbin thread feeder according to this embodiment is also provided. 
       FIG. 3  is a plan view showing the configuration of the bobbin thread feeder according to the embodiment of the present invention.  FIG. 3  shows a plan view from above in a state where the cover  18  is removed and the opening for containing the lower thread bobbin  17  is open. The bobbin thread feeder according to this embodiment is configured to dispose a horizontal rotary hook  30  below the needle plate  16 . The horizontal rotary hook  30  is configured with an outer rotary hook  29  that horizontally rotates in synchronization with the vertical movement of the needle bar  15 , and with a rotary hook  20  that is contained in the outer rotary hook  29  and provided not to rotate in synchronization with the outer rotary hook  29 . The outer rotary hook  29  has a blade point (not shown) that catches a lower thread, and forms stitches by intertwining an upper thread with a lower thread according to the vertical movement of the needle bar  15 . 
       FIG. 4  is a perspective view showing the configuration of the rotary hook  20  according to the embodiment of the present invention. As shown in  FIG. 4 , the rotary hook  20  is substantially in the shape of a cylindrical container, and has a containing portion  20   a  that can contain a lower thread bobbin  21  below the opening for containing the lower thread bobbin  17 . The lower thread bobbin  21  is removably set through the opening for containing the lower thread bobbin  17  into the containing portion  20   a.  Furthermore, a recessed portion (hooked by a finger)  20   c  for detaching the contained lower thread bobbin  21  is provided on the outer circumferential portion of the containing portion  20   a.    
     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  20   d  formed on part of the inner circumferential face of the containing portion  20   a  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  20   d  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  20   d  on the inner circumferential face of the containing portion  20   a  of the rotary hook  20 . 
       FIG. 5  is a front view of the thread tension plate  23  according to the embodiment of the present invention. As shown in  FIG. 5 , the thread tension plate  23  where a hole  23   a  is formed in the lower left portion comprises a slit  23   b  formed thereto that is a cutout, extending from substantially the central portion of the upper edge to diagonally the lower left to reach the hole  23   a.  Furthermore, a groove portion  23   c  for stably pulling the lower thread guided to the hole  23   a  out of the needle hole  16   a  of the needle plate  16  is provided near the hole  23   a  on the left of the upper edge. 
     The thread tension spring  24  is provided with a step portion  24   a  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  23   b ), and are substantially in close contact with each other at the left end portion (a portion near the hole  23   a ). 
     With this configuration, the lower thread pulled out of the lower thread bobbin  21  is guided along the slit  23   b  to the hole  23   a.  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  FIGS. 2 and 3 , the needle plate  16  is provided with a substantially linear guiding slit  27 . The angle of the guiding slit  27  substantially coincides with the direction circumscribing the lower thread bobbin  21 , that is, the direction in which the lower thread is pulled out. 
     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  23   c  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  28   a  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  28   c  that guides a lower thread to the cutter  28   b  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  20   a  of the rotary hook  20 . Then, the lower thread is pulled out of the lower thread bobbin  21 , and caught on the slit  23   b  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  23   b,  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  23   b  is lowered along the slit  23   b,  and guided to the hole  23   a.    
     When the lower thread is guided to the hole  23   a,  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  28   a  of the needle plate  16 , and thus, the lower thread is guided from the end portion of the guiding slit  27  to the cutter  28   b , along the closed-bottom groove  28   a  formed along the outer edge of the needle plate  16 . When the lower thread penetrates in the chamfering portion for the cutter  28   c,  the lower thread is cut with the cutter  28   b.    
     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  16   a  of the needle plate  16 . In this state, the lower thread is pulled out of the hole  23   a  of the thread tension plate  23  of the rotary hook  20  through the groove portion  23   c  to the needle hole  16   a,  and thus, the user does not have to be conscious of guiding the lower thread to the groove portion  23   c.  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  23   b  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.