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.

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 111a. 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 desirable 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 also desirable 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 also desirable 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.

WO-A-0043583 describes a chain stitch sewing machine having a needle bar mounted in the housing in such a way that the needle bar can be lifted and driven. At least one sewing needle is fixed on the needle head of the needle bar to which a sewing thread can be fed from a thread spool by means of a tightener and a thread guiding device. The thread guiding device comprises a thread take up controlling thread tension depending on the lift of the needle bar.

According to the present invention there is provided a double chainstitch sewing machine for forming a double chainstitch in a workpiece supplied onto a throat plate, comprising a needle bar arranged to be driven vertically by a needle bar drive mechanism due to rotation of an upper shaft, at least one needle attached to the lower end of the needle bar by a needle holder and arranged for moving vertically through the throat plate, a looper arranged to move back and forth laterally toward the needle in cooperation with the rotation of a lower shaft and a plurality of thread tension devices for adjusting the tension of the needle thread and looper thread threaded in the needle and looper respectively, characterised in that said sewing machine further comprises a fixed thread guide fixed to jaw of a sewing machine arm for leading a needle thread, a movable thread guide fixed at the lower end of the needle bar and having a thread eye for guiding the needle thread, and a thread take-up cam fixed to the jaw of the sewing machine arm and having a cam section extended in a vertical direction by intersecting with the needle thread pathway between said fixed thread guide and movable thread guide, wherein needle thread extending from the fixed thread guide to the movable thread guide is engaged with the cam section of the thread take-up cam by virtue of up and down vertical motion of the movable thread guide accompanying the corresponding vertical motion of the needle bar, and the needle thread is taken up from the thread tension device to the needle by the interaction of the movable thread guide and the cam section of the thread take-up cam.

In alternatives, there may be provided a double chainstitch sewing machine for forming a double chainstitch in a workpiece supplied onto a throat plate, comprising a needle bar moving vertically through a needle bar drive mechanism by rotation of an upper shaft, at least one needle attached to the lower end of the needle bar through a needle holder for moving vertically through the throat plate, a looper moving back and forth laterally toward the needle in cooperation with the rotation of a lower shaft, and a plurality of thread tension devices for adjusting the tension of the needle thread and looper thread threaded in the needle and looper respectively, characterised in that said sewing machine further comprises a fixed thread guide fixed to a jaw of a sewing machine arm and having right and left thread eyes disposed oppositely to each other, a movable thread guide fixed at the lower end of the needle bar and having a thread eye for passing the needle thread, and a thread take-up cam fixed to the lower end of the needle bar and having a cam section disposed between the thread eyes of the fixed thread guide, wherein the needle thread from the fixed thread guide to the movable thread guide is oscillated up and down by vertical motion of the movable thread guide accompanying the vertical motion of the needle bar, and the needle thread between the thread eyes of the fixed thread guide is inflected by vertical motion of the thread take-up cam accompanying the vertical motion of the needle bar, and the needle thread is taken up from the thread tension device to the needle by the interaction of these motions.

When 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,when the moveable 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 j aw 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, 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.

When the double chainstitch sewing machine has 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.

When 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.

When 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.

When 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.

• Fig. 1 is a perspective view showing a mechanism of a double chainstitch sewing machine of an embodiment 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 another double chainstitch sewing machine.
• 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 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.

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.

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).

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.

The needle thread take-up mechanism controls take-up of needle threads 51a, 51b 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 51a, 51b 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 51a, 51b 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 43a 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 41a, 41b, 41c having thread eyes for guiding the needle threads 51a, 51b, 51c individually. These needle thread guide members 41a, 41b, 41c 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 51a, 51b 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 43a 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 51a, 51b between the fixed thread guide 41 and movable thread guide 37, and takes up the needle threads 51a, 51b 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 43b 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 43c of the sewing machine arm 43, or may be set closer to the sewing portion of the workpiece.

An alternative double chainstitch sewing machine comprises a needle bar mechanism, a looper mechanism, a needle thread take-up mechanism, and the needle bar mechanism and looper mechanism which are the same as in the double chainstitch sewing machine in the first embodiment.

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 55a 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 43a 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 51a, 51b, 51c 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 51a, 51b, 51c. A movable thread guide 65 has a mounting part 65a affixed to the needle holder 3 by a screw 66 so as to be adjustable in vertical direction, and also has plural thread eyes 65b for passing the sewing threads 51a, 51b, 51c.

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 51a, 51b, 51c, ranging from the work piece to the thread tension device 45 through the fixed thread guide 52.

A double chainstitch sewing machine in another alternative 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.

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 81a fixed to the lower end of the longitudinal shaft 77 and a spreader piece 81b fitted to the spreader holder 81a.

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 81b of the spreader 81 oscillates as with swinging right and left.

As shown in Fig. 6, a fixed thread guide 91 is provided in the jaw 43a 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 43a 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 81a 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 81c of the spreader piece 81b 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 43c of the sewing machine arm 43, in order to shorten the thread pathway length of the upper cover thread.