Abstract:
In a double chainstitch sewing machine, a movable thread guide  37  is fixed to the lower end of a needle bar  1.  A fixed thread guide  41  and a thread take-up cam  39  are fixed to a jaw  43   a  of a sewing machine arm  43.  The thread take-up cam  39  has a cam section to be engaged with needle threads  51   a,    51   b  from the fixed thread guide  41  to the movable thread guide  37,  and takes up the needle threads oscillating up and down by vertical motion of the movable thread guide  37.  Thread take-up members such as movable thread guide  37,  fixed thread guide  41,  and thread take-up cam  39  are disposed centrally at the lower end of the needle bar near the needle and in the jaw  43   a  of the sewing machine arm  43.  As a result, there is no member for thread take-up moving at the upper side and front side of the sewing machine arm, and dangerous positions for the operator can be decreased. Further, the thread pathway length from the workpiece to the thread tension device is shortened, and the effects of thread stretch properties can be decreased.

Description:
The present invention relates to a double chainstitch sewing machine for forming stitches for applying a cover thread at the lower side or upper and lower sides of a workpiece. 
     BACKGROUND OF THE INVENTION 
     FIG. 11 shows a double chainstitch sewing machine for forming stitches related to stitch type number 407 and others designated in the United States Federal Standards No. 751a. 
     In this sewing machine, the needle thread is first passed from a thread tension device  117  into a thread eye of a first thread take-up  116  through a fixed thread guide  114 . In succession, the needle thread is passed into a thread eye of a movable thread guide  115  through a U-shaped second thread take-up  118 , and is passed into an eyelet of a needle holder  120  at the lower end of a needle bar  112  and an eyelet of a needle  119 . 
     When forming stitches for applying a cover thread at the upper and lower sides of a workpiece by this double chainstitch sewing machine, an upper cover thread mechanism disclosed in Japanese Utility Model 63-26144 is disposed beneath a sewing machine head  111   a.  The upper cover thread is supplied into the upper cover thread mechanism by way of a thread take-up for upper cover thread (not shown) provided in the first thread take-up  116  from the thread tension device  117 . 
     The movable thread guide  115  is affixed to the upper end of the needle bar  112 , and moves up and down together with the needle bar. The first thread take-up  116  is affixed to an oscillating shaft  113 , and oscillates about the shaft. All these members move up and down or oscillate outside of the sewing machine arm  111  and are hence dangerous. Accordingly, to protect the operator from danger, a guard is required, but such guard makes it difficult to pass the thread. If the guard is designed to be opened and closed for the ease of passing of thread, it leads to a cost increase. 
     Further, in this sewing machine, there is a probability of oil leak from the support parts of the needle bar projecting from the top of the sewing machine arm, and the oscillating shaft projecting to the front side of the sewing machine arm. 
     In such double chainstitch sewing machine, the needle thread from the thread tension device to the workpiece runs for a long thread pathway extending from the thread tension device to the workpiece by way of the fixed thread guide, first thread take-up, second thread take-up and movable thread guide. Accordingly, it is likely to have effects of stretchable characteristic of thread, and it is hard to obtain an optimum thread take-up amount. 
     Especially in largely stretchable thread such as woolly thread, the movable thread guide, first thread take-up and second thread take-up act more to stretch thread than to take up thread, so that the take-up action is unstable. It is hard to adjust by the first and second thread take-up amounts and is hence difficult to obtain a double chainstitch of a desired touch. Still more, since the upper cover thread is taken up at the same timing as the needle thread, it is hard to obtain a desired covering chainstitch. 
     It is hence an object of the present invention to eliminate the difficulty in threading without substantially increasing the cost, by eliminating movable thread take-up members on the upper side and front side of the sewing machine arm, and installing substituent movable thread guide and first and second thread take-ups centrally at the lower end of the needle bar or jaw of the sewing machine arm so as to decrease the dangerous positions for the operator. It is other object of the present invention to avoid the probability of oil leak from the support parts of the needle bar projecting from the top of the sewing machine arm, and the oscillating shaft projecting to the front side of the sewing machine arm. 
     It is a further object of the present invention to present a double chainstitch sewing machine capable of obtaining a desired stitch tension easily by shortening the thread pathway length from the workpiece to the thread tension device and decreasing effects of thread stretchable characteristic on take-up of needle thread, and a double chainstitch sewing machine related to a flat seam for taking up upper cover thread at optimum timing by installing a thread take-up for upper cover thread independently of a thread take-up for the needle thread. 
     SUMMARY OF THE INVENTION 
     In a first aspect of the double chainstitch sewing machine according to the present invention, a movable thread guide for guiding the needle thread is fixed to the lower end of the needle bar. A fixed thread guide is fixed to the jaw of the sewing machine arm. A thread take-up cam is also fixed to the jaw of the sewing machine arm, and the cam section of the thread take-up cam extends in the vertical direction by intersecting with the needle thread pathway between the fixed thread guide and the movable thread guide. The needle thread from the fixed thread guide to the movable thread guide is oscillated up and down from the fixed thread guide by the movable thread guide moving up and down together with the needle bar, and is supplied into the cam section of the thread take-up cam. Thus, by interaction of the movable thread guide and the cam section of the thread take-up cam, the needle thread is taken up from the thread tension device to the needle. 
     In a second aspect of the double chainstitch sewing machine according to the present invention, a movable thread guide for guiding the needle thread is fixed to the lower end of the needle bar, and a fixed thread guide having mutually opposite right and left thread eyes is fixed to the jaw of the sewing machine arm. A thread take-up cam is also fixed to the lower end of the needle bar, and the cam section of the thread take-up cam is disposed between the thread eyes of the fixed thread guide. The needle thread from the fixed thread guide to the movable thread guide is oscillated up and down from the fixed thread guide by the movable thread guide moving up and down together with the needle bar, and the needle thread between the thread eyes of the fixed thread guide is bent by the vertical motion of the cam section of said thread take-up. Thus, by interaction of the movable thread guide and the thread take-up cam, the needle thread is taken up from the thread tension device to the needle. 
     According to these aspects of the present invention, since the thread take-up oscillating vertically at the front side of the sewing machine arm and the movable thread guide moving vertically as being affixed to the upper end of the needle bar are eliminated, the operator is liberated from the danger during operation of the sewing machine at the front side and upper side of the sewing machine arm. At the same time, the support parts of the needle bar projecting from the top of the sewing machine arm, and the oscillating shaft projecting to the front side of the sewing machine arm in the conventional sewing machine can be eliminated, and probability of oil leak is avoidable. Further, the movable thread guide of the thread take-up mechanism is attached to the lower end of the needle bar, the fixed thread guide is fixed and installed at the jaw of the sewing machine arm, and the thread take-up cam is attached to the lower end of the needle bar or fixed and installed at the jaw of the sewing machine arm, so that the thread take-up action of the needle thread takes place near the needle, and the thread pathway length from the workpiece to the thread tension device can be shortened, and the thread take-up action of the needle thread is done without substantially having effects of the stretchable characteristic of the thread. 
     In a third aspect, relating to a double chainstitch sewing machine having a plurality of needles, two or more thread eyes are provided in the movable thread guide, and are disposed obliquely to the motion direction of needle bar. 
     In a fourth aspect, relating to a double chainstitch sewing machine having a plurality of needles, two or more thread eyes are provided in the movable thread guide, the fixed thread guide is composed of a plurality of thread guide members, and each thread guide member can adjust the guiding position of the needle thread individually. 
     In the double chainstitch sewing machine having a plurality of needles, the eye of each needle is different in height in order to match the timing with the eyelet of the looper, and the needles are arranged obliquely. In the present invention, since the thread eyes of the movable thread guide are arranged obliquely, or the thread guide members of the fixed thread guide can be adjusted individually, the thread take-up amount necessary for each needle thread can be assured. 
     In a fifth aspect of the double chainstitch sewing machine according to the present invention, the thread tension device for adjusting the tension of the upper cover thread is provided at the front side of the sewing machine arm, and an upper cover thread mechanism having a spreader for swinging the upper cover thread laterally to be engaged with the needle thread is provided at the jaw of the sewing machine arm, said upper cover thread mechanism is comprised a fixed thread guide for guiding the upper cover thread and a thread swing guide. The thread swing guide has a thread eye for leading the upper cover thread from the fixed thread guide to a thread lead tool, and a slot for leading the upper cover thread from the thread lead tool to the spreader. The spreader includes a thread take-up tool for taking up the upper cover thread by engaging with the upper cover thread from the fixed thread guide to the thread swing guide. 
     According to the present-invention, since the thread take-up tool for the upper cover thread is attached to the spreader, the motion of the thread take-up tool is synchronized with the motion of the spreader, and the upper cover thread is taken up independently of the thread take-up tool of the needle thread. 
     In a sixth aspect, since the upper end of the needle bar is positioned within the sewing machine frame and the length of the needle bar is shortened, it is able to reduce the weight of the needle bar and to increase the sewing machine speed. 
     In a seventh aspect, the needle bar drive mechanism comprises an oscillating shaft crossing orthogonally with the upper shaft and oscillating in cooperation with the rotation of the upper shaft, and a lever fixed to the oscillating shaft for driving the needle bar as being coupled to the upper end of the needle bar. 
     Other features and effects of the present invention will be more clearly understood in the following detailed description of the embodiments by those skilled in the art. It must be, however, noted that the technical scope of the present invention is not limited to the embodiments and the accompanying drawings alone. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing an essential mechanism of a double chainstitch sewing machine of the present invention. 
     FIG. 2 is a magnified front view of the jaw of the sewing machine in FIG.  1 . 
     FIG. 3 is a side view thereof. 
     FIG. 4 is a perspective view showing an essential mechanism of other double chainstitch sewing machine of the present invention. 
     FIG. 5 is a magnified front view of the jaw of the sewing machine in FIG.  4 . 
     FIG. 6 is a magnified front view of the jaw of the sewing machine in FIG. 2 further provided with an upper cover thread take-up mechanism. 
     FIG. 7 is a perspective view showing essential parts of a needle bar mechanism. 
     FIG. 8 is a perspective exploded view of the needle bar mechanism. 
     FIG. 9 is a perspective view of a looper mechanism. 
     FIG. 10 is a perspective view of an upper cover thread mechanism. 
     FIG. 11 is a perspective view of a conventional double chainstitch sewing machine. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A double chainstitch sewing machine in a first embodiment of the present invention comprises a needle bar mechanism, a looper mechanism, a sewing thread take-up mechanism, and is designed to form stitches of stitch type number 406 designated in the United States Federal Standard No. 751a. 
     Each mechanism is sequentially described below. 
     Needle Bar Mechanism 
     At the lower end of a needle bar  1  shown in FIG.  7  and FIG. 8, a needle  5  is provided through a needle holder  3  as shown in FIG.  2  and FIG. 5. A pi-shaped guide  7  formed at the upper end of the needle bar is coupled to a lever  11  through a pin  12 , and the lever  11  is fixed to one end of an oscillating shaft  9  which oscillates in cooperation with the upper shaft not shown. The oscillating shaft  9  is orthogonal to the upper shaft, and is supported by a bearing  13  fixed to the sewing machine frame. A crank  15  fixed to other end of the oscillating shaft  9  is coupled to a rod  17  fitted to an eccentric cam (not shown) of the upper shaft, and when the upper shaft rotates, the lever  11  fixed to the oscillating shaft  9  oscillates vertically, thereby making the needle bar  1  supported by a bush  19  to move up and down. By vertical motion of the needle bar, the needle moves up and down by penetrating through a throat plate (not shown). 
     Looper Mechanism 
     As shown in FIG. 9, a looper  21  is mounted on a platform  24  fixed to a looper shaft  23 . The looper shaft  23  is coupled to a leading end of a lever  27  fixed to an oscillating shaft  25 . A crank  29  affixed to the oscillating shaft  25  is coupled to an eccentric cam  35  of a lower shaft  33  through a rod  31 , and when the lower shaft  33  rotates, the oscillating shaft  25  oscillates, and the lever  27  swings right and left to move the looper shaft  23  reciprocally to right and left. By this reciprocal motion of the looper shaft  23 , the looper  21  moves back and forth almost horizontally toward the needle  5 . 
     Needle Thread Take-up Mechanism 
     The needle thread take-up mechanism controls take-up of needle threads  51   a,    51   b  from a thread tension device  45  to the needle  5 , and comprises a movable thread guide  37 , a thread take-up cam  39 , fixed thread guide  41 , and others as shown in FIG.  1  and FIG.  2 . The movable thread guide  37  is fixed to the needle bar  1  on the needle holder  3  as shown in FIG. 3, and has thread eyes  48  for passing the needle threads  51   a,    51   b  in oblique upward arrangement. The movable thread guide  37  moves up and down together with the needle bar  1 , and takes up the needle threads  51   a,    51   b  leaving the fixed thread guide  41  by swinging up and down. 
     The fixed thread guide  41  attached to the leading end of an L-shaped bracket  47  fitted to the outside of a jaw  43   a  of a sewing machine arm  43  by a screw  44  so that the lateral position may be adjustable, and is composed of three needle thread guide members  41   a,    41   b,    41   c  having thread eyes for guiding the needle threads  51   a,    51   b,    51   c  individually. These needle thread guide members  41   a,    41   b,    41   c  are fixed to the bracket  47  by screws (not shown) so that the vertical position may be adjustable individually, and the needle thread guide member closer to the needle bar  1  is set higher as shown in FIG.  2 . The bracket  47  has a needle thread lead plate  42  for passing the needle threads  51   a,    51   b  from the thread tension device  45  to the fixed thread guide  41 . 
     The thread take-up cam  39  is attached to the portion folded forward at one end of a bracket  49  by a screw  51  so as to be adjustable in vertical position, and the bracket  49  is fixed to the outside of the jaw  43   a  of the sewing machine arm  43  by a screw  52  so as to be adjustable in lateral position. 
     This thread take-up cam  39  has a cam section intersecting with the thread pathway between the fixed thread guide  41  and movable thread guide  37 , and extending in the vertical direction, and the cam section is engaged with the needle threads  51   a,    51   b  between the fixed thread guide  41  and movable thread guide  37 , and takes up the needle threads  51   a,    51   b  from the workpiece to the thread tension device  45  by way of the thread guide members  37 ,  41 ,  42  together with the movable thread guide  37 . 
     In the illustrated embodiment, the thread tension device  45  of the needle thread is provided at the front side of a base part  43   b  of the sewing machine arm  43 , but it is not limited to this structure. For example, to shorten the thread pathway length ranging from the workpiece to the thread tension device  45  further, the thread tension device  45  may be disposed in a wider part  43   c  of the sewing machine arm  43 , or may be set closer to the sewing portion of the workpiece. 
     A double chainstitch sewing machine in a second embodiment of the present invention comprises a needle bar mechanism, a looper mechanism, a needle thread take-up mechanism, and the needle bar mechanism and looper mechanism are same as in the double chainstitch sewing machine in the first embodiment. 
     Needle Thread Take-up Mechanism 
     The needle thread take-up mechanism differs from the needle thread take-up mechanism in the first embodiment in the following points. 
     As shown in FIG.  4  and FIG. 5, a thread take-up cam  55  is supported by a needle bar  1 . That is, a mounting part  55   a  of the thread take-up cam  55  is affixed to a bracket  57  fixed to a needle holder  3  by a screw  58  so as to be adjustable in lateral position, and the thread take-up cam  55  is supported by the needle bar  1 , and it moves up and down together with the needle bar  1  unlike the first embodiment. A fixed thread guide  52  is composed of a pair of right and left plates, and a pin  61  for fitting a holder  63  is provided at its upper end. The fixed thread guide  52  is disposed at the right and left side of the thread take-up cam  55 . The holder  63  is affixed to the outside of a jaw  43   a  of a sewing machine arm  43  by a screw  62  so as to be adjustable in vertical position. A pin  61  projecting to a side is supported by the holder  63  so as to be slidable laterally and rotatable, and is fixed to the holder  63  by a screw  64 . The fixed thread guide  52  has mutually confronting right and left thread eyes. 
     The thread take-up cam  55  is engaged with needle threads  51   a,    51   b,    51   c  passed in the fixed thread guides  52  at both sides, and moves up and down together with the needle bar  1 , thereby taking up the needle threads  51   a,    51   b,    51   c.  A movable thread guide  65  has a mounting part  65   a  affixed to the needle holder  3  by a screw  66  so as to be adjustable in vertical direction, and also has plural thread eyes  65   b  for passing the sewing threads  51   a,    51   b,    51   c.    
     The movable thread guide  65  moves up and down together with the needle bar  1  same as in the first embodiment, and takes up the needle threads  51   a,    51   b,    51   c,  ranging from the work piece to the thread tension device  45  through the fixed thread guide  52 . 
     A double chainstitch sewing machine in a third embodiment of the present invention is similar to the double chainstitch sewing machine in the first embodiment, except that the upper cover thread mechanism and upper cover thread take-up tool are further added. 
     The upper cover thread mechanism and upper cover thread take-up tool are described sequentially below. 
     Upper Cover Thread Mechanism 
     As shown in FIG. 10, an oscillating shaft  69  rotatably supported by a bushing  68  in a sewing machine arm  43  is provided parallel to an upper shaft  67 . An oscillating lever  71  attached to the oscillating shaft  69  is coupled to the upper shaft  67  through a rod  73  fitted to an eccentric cam of the upper shaft  67 , and by rotation of the upper shaft  67 , the oscillating shaft  69  oscillates. A crank arm  75  is affixed to the leading end of the oscillating shaft  69 . A longitudinal shaft  77  supported rotatably by the sewing machine arm  43  has a lever  79  at its upper end, and a spreader  81  is fixed to the lower end extended to the outside of the sewing machine arm  43 . This spreader  81  is composed of a spreader holder  81 a fixed to the lower end of the longitudinal shaft  77  and a spreader piece  81   b  fitted to the spreader holder  81   a.    
     The leading end of the lever  79  of the longitudinal shaft  77  is provided a pin  83 . The pin  83  is coupled to a cylindrical part  76  at the lower end of the crank arm  75  through a columnar peg  85 . Accordingly, when the upper shaft  67  rotates, the oscillating shaft  69  oscllates and the crank arm  75  oscillates back and forth, so that the longitudinal shaft  77  oscillates rotatably through the columnar peg  85  and the pin  83 . By rotatable oscillation of the longitudinal shaft  77 , the spreader piece  81   b  of the spreader  81  oscillates as with swinging right and left. 
     Upper Cover Thread Take-up Mechanism 
     As shown in FIG. 6, a fixed thread guide  91  is provided in the jaw  43   a  of the sewing machine arm  43 . The fixed thread guide  91  has a long thread eye  92  and a round thread eye  93  for passing the upper cover thread  89  passing from a thread tension device (not shown) through a thread lead piece  105 . The needle holder  3  has a thread lead tool  95  having a thread eye  94  for passing the upper cover thread  89 . 
     A thread swing guide  97  affixed to the outside of the jaw  43   a  of the sewing machine arm  43  by a screw  96  so as to be adjustable in vertical direction has a first thread eye  101  and a second thread eye  102  for passing the upper cover thread  89  from a cover thread take-up tool  99  to the thread lead tool  95 . A small tension device  103  is provided in the thread pathway between the two thread eyes  101 ,  102 . The upper cover thread  89  positioned between the both thread eyes is pressed to the front side of the thread swing guide  97  by means of the small tension device  103 . 
     An arc-shaped slot  98  is provided at the leading end of the thread swing guide  97 . The upper cover thread  89  from the thread lead tool  95  to the spreader  81  is passed into the arc-shaped slot  98 . The cover thread take-up tool  99  is provided in the spreader holder  81   a  attached to the lower end of the longitudinal shaft  77  shown in FIG.  10 . This cover thread take-up tool  99  has a thread eye  100  for passing the upper cover thread  89  from the fixed thread guide  91  to the first thread eye  101  of the thread swing guide  97 . 
     As shown in FIG. 6, the upper cover thread  89  is passed into the long thread eye  92  or round thread eye  93  of the fixed thread guide  91  from the thread tension device (not shown) to the thread lead piece  105 , and runs through the small tension device  103  by way of the thread eye  100  of the cover thread take-up tool  99  and the first thread eye  101  of the thread swing guide  97 . The upper cover thread  89  running through the small tension device  103  is engaged with the hook let  81   c  of the spreader piece  81   b  by way of the second thread eye  102 , thread eye  94  of the thread lead tool  95 , and slot  98  of the thread swing guide  97 . 
     While the sewing machine is running, the upper cover thread  89  is mainly taken up by the cover thread take-up tool  99 , and the thread take-up amount varies depending on the difference of passing into the long thread eye  92  and round thread eye  93  formed in the fixed thread guide  91 . This difference corresponds to the type of thread, for example, the cotton thread corresponds to the long thread eye  92 , and the woolly thread to the round thread eye  93 . 
     The cover thread take-up tool  99  is preferred to be designed so that the distance to the longitudinal shaft  77  of the upper cover thread mechanism may be variable. The thread tension device for the upper cover thread is not described in detail, but its position is preferred to be closer to the sewing part, such as the wide part  43   c  of the sewing machine arm  43 , in order to shorten the thread pathway length of the upper cover thread.