Patent Publication Number: US-6668739-B1

Title: Sewing machine

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to an improved sewing machine, and more particularly to an improved looper thread take-up structure of a sewing machine. 
     2. Description of the Prior Art 
     In sewing operation of a sewing machine, the take-up mechanism loosens the looper thread once in each stitch so as to automatically feed the thread and adjust the tension of the looper thread. 
     FIGS. 11 to  16  show a first type of conventional looper thread take-up structure  78  including a thread guide  79  and a take-up cam  84  both hidden in a lower housing  72  of the sewing machine. A first lower rotary shaft  73  is disposed in the lower housing  72  which is directly driven to further drive a second lower rotary shaft  74  via a shaft coupler  75 . The take-up cam  84  is fitted on the second lower rotary shaft  74  and rotatable along with the first lower rotary shaft  73 . 
     Referring to FIGS. 11,  15  and  16 , the thread guide  79  has a guide plate  80  formed with a slot  81  and two eyelets  82 ,  83  respectively disposed on two sides of the slot  81 . Two guide members  86 ,  87  are respectively locked on two sides of the slot  81  by screws  88 . Via a screw  94 , L-shaped coupling seat  105 , screw  106 , fixing seat  104  and screw  98 , the guide plate  80  is locked in the lower housing  72 . Each guide member  86 ,  87  has an eyelet  82 ,  83 . The thread guide  79  includes a guide bar  85 . One end of the guide bar  85  is locked on one end of the guide plate  80  via a screw  95 , coupling seat  103  and screw  97 . The other end of the guide bar  85  is extended into a fissure  91  between two cam plates  89 ,  90  of the take-up cam  84  and bridged over the other end of the guide plate  80 . The guide bar  85  has a guide slot  92  for guiding the looper thread  93  to pass therethrough (also referring to FIG.  14 ). 
     Please refer to FIGS. 11,  15  and  16 . The take-up cam  84  is composed of two cam plates  89  &amp;  90  which have identical shape and are welded into one piece. The two cam plates  89 ,  90  are spaced by a small diameter spacer wheel to define the fissure  91 . The end of the guide bar  85  is extended into the fissure  91 . 
     Referring to FIG. 14, after the looper thread  93  is passed through the eyelet  83 , the looper thread  93  is further passed through the lower knotting hook  101  as shown in FIG.  14 . The lower knotting hook  101  cooperates with an upper stitching needle  77  and an upper knotting hook  100  in sewing operation. 
     Referring to FIGS. 11,  12 ,  14 ,  15  and  16 , when the take-up cam  84  is rotated along with the second lower rotary shaft  74 , by means of the outer circumference of the take-up cam  84 , the thread is loosened in sewing operation. 
     Referring to FIGS. 11 to  16 , the first type of conventional looper thread take-up structure  78  is fixed on the second lower rotary shaft  74 . Accordingly, once the thread breaks, the take-up cam  84  in the looper thread take-up structure  78  will continuously rotate to make the thread head tangle between the cam plates  89 ,  90  welded together. The take-up cam  84  is fixed in the lower housing  72  and is undetachable. Moreover, there is no room between the looper thread take-up structure  78  and the shaft coupler  75 . Therefore, it is necessary to use a very thin artistic knife to clear up the tangling thread in a very narrow space. This is a task. 
     FIGS. 17 to  19  show a second type of conventional looper thread take-up structure  78  for solving the above problem. The looper thread take-up structure  78  is mounted beside the column  76  of the upper housing  71  of the sewing machine  70 . This makes it easier to detach the take-up cam  84  from the sewing machine. However, the two cam plates  89 ,  90  are still welded into one single piece. After the take-up cam  84  is detached, it is still difficult to clear up the tangling thread from the very narrow fissure of the take-up cam  84 . (The width of the fissure is only 2 mm.) A very thin artistic knife can be extended into the very narrow fissure to cut off the tangling thread. However, when cutting off the tangling thread, the sharp blade often incautiously cuts the polished outer circumference of the take-up cam to form a notch. After the take-up cam is reassembled, such notch tends to cut off the thread. Therefore, it is unsafe to use the artistic knife to clear up the tangling thread. 
     In addition, no matter what tool is used, it is time-consuming to clear up the tangling thread. (It often takes half day or even one day to clear up the tangling thread.) During this period, the work must be stopped. This greatly affects the production. Therefore, it is necessary to solve the above problem. 
     U.S. Pat. No. 6,263,812 of this applicant discloses a looper thread take-up mechanism for solving the problem existing in the first type of conventional looper thread take-up structure shown by FIGS. 11 and 16. In the above Patent, the take-up cam is composed of a first cam plate and a second cam plate which are separable and detachable from the rotary shaft. In case the thread tangles, the first and second cam plates can be separated to quickly and easily clear up the tangling thread. 
     With respect to the second type of conventional looper thread take-up structure  78  shown by FIGS. 17 to  19 , the take-up section starts from the looper thread take-up structure  78  and ends at the stroke position of the lower crochet needle. This take-up section is too long. That is because the looper thread take-up structure  78  is mounted on inner side of the column  76  and spaced from the stroke position of the lower crochet needle by a too long distance. It is known that the increased length of the looper thread in each take-up travel of the looper thread take-up structure  78  is limited. The longer the take-up section is, the less the looper thread is loosened. The take-up section of the second type of conventional looper thread take-up structure  78  is much longer than the take-up section of the first type of conventional looper thread take-up structure  78 . In addition, the stitching thread is extensible. Therefore, the second type of conventional looper thread take-up structure  78  shown by FIGS. 17 to  19  has a take-up effect poorer than that of the first type of conventional looper thread take-up structure  78  shown by FIGS. 11 to  16 . 
     The looper thread take-up mechanism of U.S. Pat. No. 6,263,812 of this applicant provides a measure for solving the problems existing in both the first and second types of conventional looper thread take-up structures  78 . In the above Patent, the looper thread take-up mechanism is mounted on the lower driving shaft of the sewing machine without intervening with the sewing operation, while it is still easy to clear up the thread tangling between the two cam plates of the take-up cam. 
     Besides, referring to FIGS. 15 and 16, before released, the relative phase between the take-up cam  84  and the second lower rotary shaft  74  has been well adjusted by the manufacturer, that is, the timing of the take-up cam  84  has been set. However, the preset timing is not suitable for different kinds of sewing materials and stitching threads. Too early or too late take-up operation will affect the seam on the sewing material. The take-up cam  84  has been well adjusted by specialists before released from the factory. In the case that the garment manufacturers want to re-adjust the take-up cam  84  themselves, as shown in FIGS. 15 and 16, it is necessary to unscrew the screws  96  and  99 . 
     However, referring to FIGS. 15 and 16, the problem is that the take-up cam  84  is fitted on the second lower rotary shaft  74  and locked thereon by screws  96  and  99 . By means of unscrewing the screws  96  and  99 , the take-up cam  84  can be turned relative to the second lower rotary shaft  74  so as to change the phase of the take-up cam  84  relative to the second lower rotary shaft  74 . However, there is no reference for the turning angle. Therefore, it is necessary to repeatedly unscrew and screw the screws  96  and  99  and turn the take-up cam  84  to try the position. Therefore, the garment manufactures can hardly optimally adjust the take-up cam according to the variety of the sewing material and stitching thread. 
     In case the relative phase between the take-up cam  84  and the second lower rotary shaft  74  can be conveniently and accurately adjusted by the garment manufacturers themselves, an optimal sewing effect can be achieved. 
     SUMMARY OF THE INVENTION 
     It is therefore a primary object of the present invention to provide an improved sewing machine which is able to achieve the following purposes: 
     1. A slide interval is defined between the looper thread take-up structure and the shaft coupler. The first and second cam plates can slide along the second lower rotary shaft to the slide interval and respectively slide to two sides and separate from each other. Therefore, the tangling thread between the two cam plates can be easily cleared up. 
     2. A recess is formed on a portion of the second lower rotary shaft where the looper thread take-up structure is fitted. A tool can be extended into the recess to cut off the thread tangling around the second lower rotary shaft so as to more easily clear up the tangling thread. 
     3. The take-up structure of the present invention can be still mounted in the lower housing of the sewing machine in the original position. Therefore, the take-up structure is close to the lower knotting hook and a better take-up effect can be achieved. 
     4. The relative phase between the take-up cam and the second lower rotary shaft can be easily and quickly adjusted so as to achieve an optimal sewing effect. 
     5. Without any specialist skilled in sewing machine, a general sewer herself can easily quickly complete the adjustment. 
     According to the above object, the sewing machine of the present invention includes a lower housing, a first lower rotary shaft, a second lower rotary shaft, a shaft coupler and a looper thread take-up structure. The first lower rotary shaft is disposed in a section of the lower housing and drivingly connected with a power source. The second lower rotary shaft is disposed in another section of the lower housing and drivingly connected with a lower stitching needle. The second lower rotary shaft is coaxial with the first lower rotary shaft. The shaft coupler couples the first lower rotary shaft with the second lower rotary shaft, whereby the first lower rotary shaft and the second lower rotary shaft are drivingly connected to rotate along with each other. The looper thread take-up structure is fitted on the second lower rotary shaft. The looper thread take-up structure includes a thread guide and a take-up cam. The thread guide includes a guide plate formed with a slot and two eyelets respectively disposed on two sides of the slot. The take-up cam is fitted on the second lower rotary shaft and passed through the slot of the guide plate. 
     The take-up cam includes a first take-up cam plate and a second take-up cam plate. The first cam plate has an outer circumference and a shaft hole. By means of the shaft hole, the first cam plate is key-fitted on the second lower rotary shaft. The first cam plate is rotatable along with the second lower rotary shaft and axially slidable along the second lower rotary shaft. The second cam plate has an outer circumference and a shaft hole. By means of the shaft hole, the second cam plate is key-fitted on the second lower rotary shaft. The second cam plate is rotatable along with the second lower rotary shaft and axially slidable along the second lower rotary shaft. The first and second cam plates define therebetween a gap and are separable from each other for easily clearing up tangling thread. A slide interval is defined between the looper thread take-up structure and the shaft coupler, whereby the second cam plate can slide along the second lower rotary shaft to the slide interval and separate from the first cam plate for easily clearing up the tangling thread. 
     A recess is formed on a portion of the second lower rotary shaft where the looper thread take-up structure is fitted. A tool can be extended into the recess to cut off the thread tangling around the second lower rotary shaft. 
     The guide plate of the thread guide is movably connected with the lower housing. By means of changing the position of the guide plate relative to the second lower rotary shaft, the positions of the eyelets on two sides of the slot of the guide plate relative to the take-up cam are changeable so as to adjust the take-up timing. 
     The guide plate has a fixing slot. A bolt is passed through the fixing slot to lock the guide plate on the lower housing. By means of changing the position of the guide plate relative to the second lower rotary shaft, the positions of the eyelets on two sides of the slot of the guide plate relative to the take-up cam are changeable so as to adjust the take-up timing. 
     Scales are marked on one side of the fixing slot of the guide plate to indicate the position of the guide plate, whereby the take-up timing can be quickly and easily adjusted. 
     The lower housing is provided with a bracket having an arched guide section. The circular center of the arched guide section is positioned at the axis of the second lower rotary shaft. The guide plate is slidable along the arched guide section of the bracket. The eyelets on two sides of the slot of the guide plate revolve in an arched track about the axis of the second lower rotary shaft so as to adjust the take-up timing. 
    
    
     The present invention can be best understood through the following description and accompanying drawings wherein: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective exploded view of the present invention; 
     FIG. 2 is a perspective assembled view of the present invention mounted in the lower housing of the sewing machine; 
     FIG. 3 is a perspective view of a common sewing machine in which the present invention is mounted; 
     FIG. 4 shows the threading of the present invention; 
     FIG. 5 is a sectional view taken along line  5 — 5  of FIG. 2; 
     FIG. 6 is a view according to FIG. 5, in which the guide plate is adjusted from the first position of FIG. 5 to a second position; 
     FIG. 7 is a sectional view taken along line  7 — 7  of FIG. 2; 
     FIG. 8 is a sectional view taken along line  8 — 8  of FIG. 2; 
     FIG. 9 shows that when clearing up the tangling thread, the two cam plates are moved to two sides in accordance with the present invention; 
     FIG. 10 shows that a tool is used to clear up the thread tangling around the second lower rotary shaft; 
     FIG. 11 is a perspective exploded view a conventional take-up structure of the prior art 1; 
     FIG. 12 is a perspective assembled view of the conventional take-up structure mounted in the lower housing of the sewing machine in accordance with the prior art 1; 
     FIG. 13 is a perspective view of a common sewing machine in which the present invention is mounted in accordance with the prior art  1 ; 
     FIG. 14 shows the threading of the conventional take-up structure in accordance with the prior art 1; 
     FIG. 15 is a sectional view taken along line  15 — 15  of FIG. 12, showing that the lower rotary shaft and the guide plate are positioned in a first position; 
     FIG. 16 is a view according to FIG. 15, showing that the lower rotary shaft must be moved to a second position for moving the guide plate to the second position; 
     FIG. 17 is a perspective view of another type of conventional sewing machine of the prior art 2; 
     FIG. 18 is a view of a part of the conventional sewing machine of FIG. 17, seen in the direction of arrow  18 ; and 
     FIG. 19 is a sectional view taken along line  19 — 19  of FIG.  18 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Please refer to FIGS. 1 to  4 . The sewing machine  20  of the present invention includes a lower housing  21 , an upper housing  22 , a first lower rotary shaft  25 , a second lower rotary shaft  26  and a shaft coupler  27 . The first lower rotary shaft  25  is disposed in the lower housing  21  and drivingly connected with a power source. The second lower rotary shaft  26  is also disposed in the lower housing  21  and coupled with the first lower rotary shaft  25  via the shaft coupler  27 . 
     The looper thread take-up structure  23  is fitted on the second lower rotary shaft  26 , including a thread guide  29  and a take-up cam  46 . The thread guide  29  has a guide plate  30  formed with a slot  31  and two eyelets  32 ,  33  respectively disposed on two sides of the slot  31 . The take-up cam  46  is fitted on the second lower rotary shaft  26  of the sewing machine  20  and passed through the slot  31  of the guide plate  30 . Two guide members  47 ,  48  are respectively locked on two sides of the slot  31  of the guide plate  30  by screws  49 . Each guide member  47 ,  48  has an eyelet  32 ,  33 . The take-up cam  46  is upward passed through the slot  31  of the guide plate  30  from lower side thereof. The thread guide  29  further includes a guide bar  50 . One end of the guide bar  50  is locked on one end of the guide plate  30  via a screw  51 , coupling seat  52  and screw  57 . The other end of the guide bar  50  is extended into a fissure  55  between two cam plates  39 ,  40  of the take-up cam  46  and bridged over the other end of the guide plate  30 . The guide bar  50  has a guide slot  56  for guiding the looper thread  58  to pass therethrough to the lower knotting hook  59  (referring to FIG.  4 ). The lower knotting hook  59  cooperates with the upper stitching needle  28  and the upper knotting hook  60  to complete the sewing operation. 
     The present invention is characterized in that as shown in FIGS. 1 to  4 , the looper thread take-up structure  23  is fitted on the second lower rotary shaft  26 . The looper thread take-up structure  23  includes a first take-up cam plate  39  and a second take-up cam plate  40 . The first cam plate  39  has an outer circumference  41  and a shaft hole  53 . By means of the shaft hole  53 , the first cam plate  39  is key-fitted on the second lower rotary shaft  26  and rotatable along therewith. In addition, the first cam plate  39  is axially slidable along the second lower rotary shaft  26 . The second cam plate  40  has an outer circumference  42  and a shaft hole  54 . By means of the shaft hole  54 , the second cam plate  40  is key-fitted on the second lower rotary shaft  26  and rotatable along therewith. In addition, the second cam plate  40  is axially slidable along the second lower rotary shaft  26 . The first and second cam plates  39 ,  40  define therebetween a cam plate gap G. Moreover, the first and second cam plates  39 ,  40  are separable from each other for easily clearing up the tangling thread. 
     Referring to FIGS. 2,  7 ,  8 ,  9  and  10 , a slide interval D is defined between the looper thread take-up structure  23  and the shaft coupler  27 . The first and second cam plates  39 ,  40  can slide along the second lower rotary shaft  26  to the slide interval D and respectively slide to two sides and separate from each other as shown in FIG.  10 . This makes it easier to clear up the tangling thread. 
     Referring to FIGS. 1,  9  and  10 , a recess  61  is formed on a portion of the second lower rotary shaft  26  where the looper thread take-up structure  23  is fitted. A tool  38  can be extended into the recess  61  to cut off the thread  43  tangling around the second lower rotary shaft  26 . 
     Referring to FIGS. 1 to  4 , the guide plate  30  of the thread guide  29  is movably connected with the lower housing  21 . By means of changing the position of the guide plate  30  relative to the second lower rotary shaft  26 , the positions of the eyelets  32 ,  33  on two sides of the slot  31  of the guide plate  30  relative to the take-up cam  46  are changeable so as to adjust the take-up timing. 
     Referring to FIGS. 1,  5  and  6 , the guide plate  30  has an arched fixing slot  34 . A bolt  45  is passed through the fixing slot  34  to lock the guide plate  30  on the lower housing  21 . By means of changing the position of the guide plate  30  relative to the second lower rotary shaft  26 , the positions of the eyelets  32 ,  33  on two sides of the slot  31  of the guide plate  30  relative to the take-up cam  46  are changeable so as to adjust the take-up timing. 
     Referring to FIGS. 1,  5  and  6 , scales  44  are marked on one side of the fixing slot  34  of the guide plate  30  to indicate the position of the guide plate  30 , whereby the take-up timing can be quickly and easily adjusted. 
     Referring to FIGS. 5 and 6, the lower housing  21  is provided with a bracket  35  having an arched guide section  36  which is locked on the lower housing  21  by means of screws  62 . The circular center of the arched guide section  36  is preferably positioned at the axis  37  of the second lower rotary shaft  26 . (It is also acceptable that the circular center of the arched guide section  36  is displaced from the axis of  37  of the second lower rotary shaft  26 .) The guide plate  30  is slidable along the arched guide section  36  of the bracket  35 , whereby the eyelets  32 ,  33  on two sides of the slot  31  of the guide plate  30  revolve in an arched track about the axis  37  of the second lower rotary shaft  26  so as to adjust the take-up timing. 
     According to the above arrangement, the present invention has the following advantages: 
     1. The slide interval D is defined between the looper thread take-up structure  23  and the shaft coupler  27 . The first and second cam plates  39 ,  40  can slide along the second lower rotary shaft  26  to the slide interval D and respectively slide to two sides and separate from each other. Therefore, the tangling thread between the two cam plates  39 ,  40  can be easily cleared up. 
     2. The recess  61  is formed on a portion of the second lower rotary shaft  26  where the looper thread take-up structure  23  is fitted. A tool  38  can be extended into the recess  61  to cut off the thread  43  tangling around the second lower rotary shaft  26  so as to more easily clear up the tangling thread. 
     3. The take-up structure of the present invention is mounted in the lower housing  21  of the sewing machine in the original position. Therefore, the take-up structure is close to the lower knotting hook and a better take-up effect can be achieved. 
     4. The relative phase between the take-up cam and the second lower rotary shaft can be easily and quickly adjusted so as to achieve an optimal sewing effect. 
     5. Without any specialist skilled in sewing machine, a general sewer herself (generally female) can easily quickly complete the adjustment. 
     The above embodiments are only used to illustrate the present invention, not intended to limit the scope thereof. Many modifications of the above embodiments can be made without departing from the spirit of the present invention.