This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2008-248637 filed in Japan on Sep. 26, 2008, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a sewing machine for covering chain stitch having a cover thread looper which arranges a top cover thread on a surface of a cloth in which stitches are formed by a plurality of needles.
2. Description of Related Art
In a sewing operation of a cloth having high elasticity such as knit fabric, a sewing machine for covering chain stitch described in Japanese Patent Publication Laid-Open No. 2008-142498 is widely employed. A stitch formed by the sewing machine for covering chain stitch has excellent elasticity and strength. The sewing machine for covering chain stitch includes a cover thread looper. The cover thread looper arranges a top cover thread on a surface of a cloth on which stitches are formed by a plurality of needles, so as to make the top cover thread regularly intertwine with the stitches. The top cover thread arranged by the cover thread looper makes appearance of the stitch excellent.
The sewing machine for covering chain stitch includes a looper (not shown) in a bed which supports a lower side of the cloth 200. The looper holds a looper thread and moves forward and rearward in an arranging direction (right and left direction) of the needles 41a to 41d. The forward and rearward movement of the looper is generated in synchronization with vertical movements of the needles 41a to 41d, and a stitch is formed on the cloth 200.
The sewing machine for covering chain stitch further includes a cover thread looper 90 and a cover thread guide 93 arranged on one side (right side) in the arranging direction of the needles 41a to 41d. The cover thread looper 90 is an arc member which swings in the right and left direction on the front side of the needles 41a to 41d. The cover thread looper 90 includes a thread hook 90a inside of the tip end. A top cover thread 100 is hooked on the thread hook 90a. The cover thread guide 93 includes a guide hole 93a which is long in the front and back direction, and the guide hole 93a is located on the upper side of the cover thread looper 90. A front end of the guide hole 93a is located frontward of positions where the needles 41a to 41d are arranged, and a back end of the guide hole 93a is located backward of the positions where the needles 41a to 41d are arranged.
The top cover thread 100 is supplied from above, passes through a small hole 44a of the thread-guide member 44 provided on the needle stopper 45 as shown in the drawing. The top cover thread 100 is connected to the cloth 200 through a guide hole 93a of the cover thread guide 93. The top cover thread 100 is hooked on the thread hook 90a of the cover thread looper 90 swinging below the cover thread guide 93, and arranged on a surface of the cloth 200.
When the cover thread looper 90 is in the receding position, as shown in
An appropriate tension is applied to the top cover thread 100. Thus, the top cover thread 100 slides in the guide hole 93a as the cover thread looper 90 is pulled out. Then, the top cover thread 100 moves to a back end of the guide hole 93a, and the top cover thread 100 is extended between the guide hole 93a and the thread hook 90a.
As shown in
In the conventional sewing machine for covering chain stitch, there is a problem that generates sewing failures called “thread-stitching” and “stitch skipping” deteriorating the appearance. The “thread-stitching” is a sewing failure generated when a needle pierces through the top cover thread 100 arranged on the cloth 200 as shown with a symbol “A” in
The top cover thread 100 is located under the tip end of the needle 41d and behind the needle 41d as described above. The needle thread 42d extending from the needle 41d toward the cloth 200 may come into contact with the top cover thread 100 located at such a position from behind.
Although a tension is surely applied to the top cover thread 100, the tension of the top cover thread 100 is generally smaller than that of the needle thread 42d. Thus, the top cover thread 100 is pushed by the needle thread 42d which contacts the top cover thread 100 from behind, and the top cover thread 100 is moved frontward as shown with broken lines in
When the top cover thread 100 passes directly below the needle 41c, the lowering needle 41c pierces through the top cover thread 100, and the “thread-stitching” is generated. When the top cover thread 100 passes frontward the needle 41c, the lowering needle 41c passes behind the top cover thread 100 and the “stitch skipping” is generated.
The present invention has been accomplished in view of the above circumstances, and it is an object of the invention to provide a sewing machine for covering chain stitch capable of reliably arranging a top cover thread at a predetermined position on a surface of a cloth, and capable of forming a stitch having excellent appearance without generating sewing failures such as “thread-stitching” and “stitch skipping”.
A sewing machine for covering chain stitch of the first invention includes a plurality of needles arranged in a direction intersecting with a sending direction, a cover thread guide which is arranged on one side of the needles in an arrangement direction and which has a guide hole being long in a front and back direction, and a cover thread looper which is located below the cover thread guide and which moves frontward and backward so as to come across a front side of the needles, in which a top cover thread passing through the guide hole is caught by the advancing cover thread looper and is pulled out, the top cover thread being guided through the guide hole and being arranged on a surface of the cloth, wherein the sewing machine for covering chain stitch further includes a thread push member that moves frontward and backward at a location above the cover thread guide in association with the cover thread looper, pushes by the backward movement the top cover thread which passes through the guide hole, and forcibly moves the top cover thread to a back side of the guide hole.
In the present invention, the thread push member moves frontward and backward at a location above the cover thread guide in association with the cover thread looper. When the thread push member moves backward, it presses the top cover thread which passes through a guide hole of the cover thread guide. The top cover thread is forcibly moved to a location near a back end of the guide hole by the pushing action of the thread push member, the top cover thread keeps the moved position against a tension of the needle thread which comes into contact the top cover thread from behind, and the top cover thread is reliably arranged at a predetermined position on a surface of a cloth.
According to the sewing machine for covering chain stitch of the second invention, the thread push member of the first invention is mounted on a drive shaft of the cover thread looper, and the sewing machine for covering chain stitch further includes a swinging rod swinging in accordance with repetitive pivot movement of the drive shaft.
In this invention, the thread push member is mounted on the top cover shaft which drives the cover thread looper, and a drive system for the cover thread looper and the thread push member are commonly used, and the object can be achieved with a simple structure.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.
The present invention will be described in detail based on the drawings which show a preferable embodiment thereof.
The sewing machine for covering chain stitch shown in the drawings is constituted as a longitudinal cylindrical sewing machine in which a small-diameter cylindrical bed 2 projects from a lower portion of one side of a sewing machine body 1, and a sewing machine arm 3 projects substantially in parallel to the cylindrical bed 2 above the cylindrical bed 2 on the same side.
A needle plate 20 is provided on an upper surface of a tip end of the cylindrical bed 2. A sending device and a looper (both not shown) are provided in the cylindrical bed 2 below the needle plate 20. A needle rod 4 is supported on a tip end of the sewing machine aim 3. Four needles 41a to 41d are mounted on a lower end of the needle rod 4 projecting downward from the sewing machine arm 3 through a needle stopper 45 (see
The cloth 200 (see
A transmission shaft 6 is provided at an upper portion in the sewing machine body 1. The transmission shaft 6 is substantially in parallel to the sewing machine main shaft 5, and the transmission shaft 6 is supported at a position corresponding to a height of the projecting portion of the sewing machine arm 3. Through a transmission belt 60 wound around a transmission pulley 61 of one end (right end), the transmission shaft 6 is connected to a transmission pulley 62 of the other end (right end) of the sewing machine main shaft 5. The transmission shaft 6 is rotated around a center axis by rotation of the sewing machine main shaft 5 transmitted through the transmission belt 60.
A needle rod drive shaft 7 is provided near the needle rod 4 inside a tip end of the sewing machine aim 3. The needle rod drive shaft 7 is in almost parallel to the sewing machine main shaft 5 and the transmission shaft 6. The needle rod drive shaft 7 is connected to a transmission pulley 62 arranged on an end of the transmission shaft 6 on the same side in a side by side relation with the transmission pulley 61 by a transmission belt 70 wound around a transmission pulley 71 on one end (right end). The needle rod drive shaft 7 rotates around a center axis by rotation of the transmission shaft 6 transmitted through the transmission belt 70.
The needle rod drive shaft 7 is connected to the needle rod 4 through a movement-converting mechanism 8 shown in
A needle stopper 45 is fixed to a lower end of the needle rod 4. The four needles 41a to 41d are mounted on the needle stopper 45 in this order from left to right. A retainer 43 is mounted on the needle stopper 45 on the left side of the needle 41a. The needles 41a to 41d and the retainer 43 mounted on the needle stopper 45 are moved upward and downward between the top dead center and the bottom dead center by the vertical movement of the needle rod 4. The needles 41a to 41d moving upward and downward sew a cloth on the needle plate 20 in cooperation with the looper which moves forward and rearward. When the retainer 43 moves downward, the retainer 43 reaches the inside of the cylindrical bed 2 together with the needles 41a to 41d, and the retainer 43 catches and holds a looper thread held by the looper as is known. The top cover device 9b includes a top cover shaft 9, a cover thread looper 90 and a thread push member 94. The top cover shaft 9 is supported by bearing bushes 91 and 92 at upper and lower walls of the sewing machine arm 3, and the top cover shaft 9 can rotate around a vertical axis.
A lower end of the top cover shaft 9 projects downward of the sewing machine arm 3, and the cover thread looper 90 is mounted on the projecting end of the top cover shaft 9 through a looper stage 99. The cover thread looper 90 includes a shaft portion extending downward from the looper stage 99 and a curved portion which is continued to a lower end of the shaft portion and curved into an arc shape on a plane (plane which is substantially in parallel to the needle plate 20) substantially intersecting with an axial direction. The curved portion of the cover thread looper 90 is provided with a thread hook 90a which inwardly projects near the tip end. The thread push member 94 is mounted on a holding stage 95 which is integrally provided on the looper stage 99. The thread push member 94 includes a connecting shaft 94a extending downward from the holding stage 95, and a swinging rod 94b which is formed by bending a lower portion of the connecting shaft 94a substantially at right angles and which is substantially in parallel to the needle plate 20.
The top cover transmission mechanism 9a transmits rotation movement of the needle rod drive shaft 7 to the top cover shaft 9, and repeatedly turns the top cover shaft 9. The top cover transmission mechanism 9a includes a top cover lever 92b, a swing arm 91a, a top cover crank arm 92a and a connection link 98a. The top cover lever 92b is supported by a support shaft 82 which is common to the needle swing arm 81. Thus, the top cover lever 92b can swing around the support shaft 82.
As shown in
The swing aim 91a is located between upper and lower bearing bushes 91 and 92 and fixed to the top cover shaft 9. As shown in
With the above structure, rotation movement of the needle rod drive shaft 7 is transmitted to the top cover lever 92b through the top cover crank 73 and the top cover crank arm 92a. The top cover lever 92b swings around the support shaft 82, and one period of the top cover lever 92b corresponds to one rotation of the needle rod drive shaft 7. This swinging angle can be changed by adjusting a connected position between the top cover crank arm 92a and the top cover lever 92b. The swinging movement of the top cover lever 92b generated in this manner is transmitted to the swing arm 91a through the connection link 98a, and the top cover shaft 9 on which the swing arm 91a is mounted repeatedly turns through an angle corresponding to the swinging angle of the top cover lever 92b.
A cover thread guide 93 similar to a guide of the conventional sewing machine for covering chain stitch is arranged at a position on the cover thread looper 90. As shown in
The swinging rod 94b of the thread push member 94 mounted on the top cover shaft 9 is located at a higher position than the plate portion of the cover thread guide 93, and a tip end of the swinging rod 94b is located frontward of a front end of the guide hole 93a. The swinging rod 94b of the thread push member 94 located in such a position swings in synchronization with the cover thread looper 90 in accordance with repetitive pivot movement of the top cover shaft 9. The swinging movement of the swinging rod 94b is generated in a range which passes through an upper side of the guide hole 93a provided in the cover thread guide 93 and reaching a back end portion from a front side frontward of a front end of the guide hole 93a.
As described above, the needles 41a to 41d move upward and downward between the top dead center and the bottom dead center, and the cover thread looper 90 and the thread push member 94 swing between the receding position shown in
When the cover thread looper 90 is in the receding position, the thread hook 90a is opposed to a back side of the top cover thread 100 passing near a front end of the guide hole 93a as shown in
The cover thread looper 90 advances as shown with a solid arrow in
When the needles 41a to 41d move upward and reach the top dead center, the cover thread looper 90 reaches the advancing position shown in
Positions of the lower ends of the four needles 41a to 41d are different from each other as described above. When the needles 41a to 41d are at the top dead center, the lower ends of the left two needles 41a and 41b are located below the top cover thread 100, and the lower ends of the right two needles 41c and 41d are located above the top cover thread 100. Therefore, the top cover thread 100 tightened between the guide hole 93a and the thread hook 90a comes into contact with a front portion of the needle 41b and bends as shown in
After the needles 41a to 41d reach the top dead center, the needles 41a to 41d move downward as shown by an arrow of broke line in
The needles 41a to 41d further move downward and penetrate the cloth 200 as shown in
Even in the sewing machine for covering chain stitch according to the present invention which is operated as described above, the needle thread 42d extending from the needle hole of the right needle 41d to the cloth 200 may come into contact with the top cover thread 100 passing the back side of the needles 41a to 41d from behind and may apply a frontward pushing force, as explained using
However, in the sewing machine for covering chain stitch according to the present invention, the top cover thread 100 is pushed backward by the swinging rod 94b of the thread push member 94, and is prevented from moving away from the vicinity of the back end of the guide hole 93a formed in the cover thread guide 93. Therefore, the top cover thread 100 is not moved frontward by a force applied from the needle thread 42d which comes into contact from behind, and the tightened attitude of the top cover thread 100 is not varied.
In the sewing machine for covering chain stitch of the present invention, it is possible to prevent the sewing failure such as “thread-stitching” and “stitch skipping” shown in
As apparent from the detailed description, in the sewing machine for covering chain stitch according to the present invention, the top cover thread passing through the guide hole of the cover thread guide is pressed by the thread push member which moves frontward and backward in association with the cover thread looper, and forcibly moves it backward of the guide hole. Thus, the top cover thread is arranged at a predetermined position on the surface of the cloth without being affected by contact with the needle thread. Therefore, it is possible to prevent the sewing failure such as “thread-stitching” and “stitch skipping” from being generated, and covering chain stitches can stably be formed with excellent appearance.
As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.
Number | Date | Country | Kind |
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2008-248637 | Sep 2008 | JP | national |