Apparatus and method for making a stitch and a thread chain

Abstract

 A thread support means (27) traverses the rear side of needles (19, 21) in cooperation with a sewing machine main shaft and supports thread loops (11b, 13b) consecutive toward the needles from rows of a seam. When the needles penetrate through a thin fabric, the thread support means (27) prevents the thin fabric from being pushed down by the thread loops and sinking into the needle holes of a needle plate (29) together with the needles and causing distortion thereby. When the needles (19, 21) rise, the thread support means (27) slips out of the thread loops (11b, 13b), while the fabric advances by the length of one stitch, and the thread loops (11b, 13b) are absorbed into a newly formed stitch to be tightened appropriately, thereby forming a uniform seam without wrinkle.

Description

Field of the Invention

[0001] The present invention relates to a method and apparatus for sewing a fabric without causing distortion in a fabric due to pulling of a thread for forming a seam.

Description of the Prior Art

[0002] When forming a seam on a fabric with a lock stitch sewing machine, a double chain stitch sewing machine, or the like, if the fabric is thin and soft, the seam is pulled to contract by the tension of the sewing thread, or the fabric sinks into the needle hole of the needle plate of the sewing machine when the needle penetrates into the fabric, and a seam-puckering is likely to occur along the seam.

[0003] In the lock stitch sewing machine, in order to prevent such seam-puckering, it is attempted, for example, to sew with a shape retaining paper fitted to a thin fabric.

[0004] On the other hand, with an interlock stitch sewing machine or a double chain stitch sewing machine for forming a double chain stitch with two or three needles and a looper, when forming a double chain stitch without upper cover thread on a fabric with two needles and three threads, or three needles and four threads (U.S. Federal stitch type 406 or 407), plural rows of seam appear on the top of the fabric, and plural rows of seam and an interposed cover thread (looper thread) appear on the lower surface of the fabric. When forming such seams on a thin fabric, the plural rows of seam are pulled to each other by the cover thread, or when the needles penetrate through the fabric, the fabric sinks into the needle holes of the needle plate together with the needles, thereby often the top surface of the fabric between the rows bulges up like a ridge. Similar problems occur when forming a lock stitch with two needles and three threads or three needles and four threads (e.g. U.S. Federal stitch type 309 or 311).

[0005] The technique to solve such problems requires great skill such as adjusting thread tensions delicately, and sewing carefully with reduced work speed of the sewing machine.

[0006] Moreover, in the interlock stitch or double chain stitch sewing machine of two or three needles, without using top cover thread, in order to raise the sewing efficiency, that is, to feed the fabrics one after another by continuously operating the sewing machine, it is necessary to form a thread chain continuously and smoothly between fabrics. In this kind of sewing machine, hitherto, after sewing one fabric and sending it out, the thread chain formed consecutive to the sewing end is pushed down by the needles descending for forming the next seam and droops beneath the needle plate, and when the looper picks up the thread loops formed with the needles rising from the bottom end point, it simultaneously catches the drooping thread chain, so that the feed dog cannot send out the thread chain. When there is no fabric, the right and left needles cannot maintain their space between two rows of the seam, nor make a uniform thread chain, and the thread chain formed by them drops below the needle plate, so that it cannot be sent out by the feed dog, and thus the thread chain cannot be drawn out continuously owing to these reasons.

[0007] To solve the problems, Japanese Laid-open Patent No. 3-23887 (U.S. Pat. 5,027,728) proposes a sewing machine in which a thread brake device is projecting at the lower side of the stitch formation tongue formed toward the cloth feed direction from the needle hole of the needle plate, and the thread chain drawn out from the tongue consecutively to the fabric sewing end is held by the thread brake device, thereby preventing the thread chain from dropping due to fall of the needle, and the formed thread chain is sent out by a feed dog disposed in the feed direction, and thus the thread chain is sent out.

SUMMARY OF THE INVENTION

[0008] A primary object of the invention is to provide a method and apparatus for sewing a fabric in a favorable appearance, without causing puckers, specially for sewing a thin fabric.

[0009] Another object of the invention is to form a thread chain reliably, consecutively to an end seam on a fabric.

[0010] In the invention, a sewing machine with one needle or a sewing machine with plural needles is provided with a thread support means which traverses across the running direction of a fabric at the fabric delivery side of the needle in cooperation with the rising and descending motion of the needle.

[0011] The thread support means advances onto the fabric at the delivery side of the needle when the needle descends to form a next seam, and the thread support means receives and supports the needle thread consecutive from the seam to the needle, and retreats aside when the needle rises.

[0012] While the needle descends and penetrates through the fabric, the loop of the needle thread from the seam to the needle is supported by the thread support means, and the fabric is prevented from sinking into the needle holes of the needle plate as being pushed down with descending needle and needle thread loop, so that the fabric is free from distortion. When the needle rises, the thread support means is put aside, and therefore the needle thread is appropriately tightened together with rising of the needle, so that a neat seam is formed.

[0013] The invention is preferably applied to a sewing machine comprising a plurality of needles moving up and down, a single looper for forming a seam in cooperation with the needles by traversing in the needle aligning direction under a needle plate, and a fabric feed device.

[0014] A thread support means supports the needle thread between the seam and needle, and thereby supports the thread chain consecutive to the tail end of one fabric and the initial end of a next fabric, so that the thread chain may be drawn out smoothly by preventing sinking of thread chain along with descending motion of the needles.

[0015] These and other objects of the invention will become more apparent to those skilled in the art from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Fig. 1 is a perspective view of a double chain stitch sewing machine of the invention.

[0017] Fig. 2 is a perspective view of a seam sewn by using the double chain stitch sewing machine.

[0018] Figs. 3-7 are fragmentary perspective views showing process of forming a seam of double chain stitch by using the double chain stitch sewing machine in Fig. 1, but in which the fabric and needle plate are not shown.

[0019] Fig. 8 is a fragmentary perspective view showing process of forming a thread chain by using the double chain stitch sewing machine shown in Fig. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] Fig. 1 shows a sewing machine 17 for forming a double chain stitch (U.S. Federal stitch type 406) composed of two needle threads 11 and 13, and a single looper thread 15. Under a head 17a at one end of the sewing machine arm 17c, a right needle 19 and a left needle 21 moving up and down in cooperation with the sewing machine main shaft, a presser foot 23, and a thread support 27 traversing on the presser foot 23 at the delivery side (the front side of a presser bar 25) of the needles 19, 21 are provided. Lateral oscillations of the thread support 27 can be adjusted in timing with the vertical move of the needles 19, 21 corresponding to the properties of the fabric and some sewing conditions by varying its mounting position.

[0021] A sewing machine bed 17b includes a needle plate 29, feed dogs 31 moving up and down through slits for the feed dogs on the needle plate 29 to cooperate with the presser foot 23 and send the fabric, and a looper 35 moving reciprocally in the direction of arrangement of the needles 19, 21 to form the double chain stitch in cooperating with the needles 19, 21. At the base side of a sewing machine arm 17c, a thread tension adjusting device 33 for applying tension individually to the two needle threads 11 and 13, and looper thread 15 is provided. This device 33 comprises a thread adjusting device group 33a for sewing, and a thread adjusting device group 33b for forming thread chain. Either thread adjusting group is made active by a changeover device, which is not shown, while the other thread adjusting device is inactive.

[0022] In a sewing operation, the thread adjusting device group 33a is changed over by the changeover device to be active, and the thread adjusting device 33b to be inactive, thereby starting the sewing machine 17.

[0023] Fig. 3 to Fig. 7 show forming processes to form a double chain stitch as shown in Fig. 2 with the sewing machine 17. The looper 35 advances by picking up the thread loops 11, 13a formed immediately before, and the needles 19, 21 with the needle threads 11, 13 descend for forming next seam, while the thread support 27 traverses before the needle threads 11, 13 extending from the thread loops 11a, 13a to the needles 19, 21, and to the rear side of the needles 19, 21 (Figs. 3, 4). When the fabric (not shown) is fed with the feed dog 31 by the length of one seam and the needles 19, 21 penetrate through the fabric, the thread loops 11b, 13b formed on the top surface of the fabric are supported by the thread support 27 (Figs. 4, 5).

[0024] While the needles 19, 21 penetrate through the fabric, pass through the triangles formed by the looper 35 reaching the forward end, looper thread 15 and thread loops 11a, 13a (Fig. 5), and descend to the bottom end position, the looper 35 retreats from the forward end and withdraws from the needle thread loops 11a, 13a to reach the backward end, and the thread support 27 supports the thread loops 11b, 13b to move advance, and reaches the advance end (Fig. 6). While the needles 19, 21 are descending in this way, the thread loops 11b, 13b are in a state being supported by the thread support 27, and therefore the top of the fabric is not pressed directly with the thread loops 11b, 13b, and hence when the needles 19, 21 penetrate through the fabric, the thread loops 11b, 13b do not push the fabric into the holes of the needle plate, so that the fabric will not be distorted by needle threads.

[0025] The thread loops newly formed when the needles 19, 21 rise from the bottom end position are picked up as the looper 35 advances, while the thread support 27 retreats to slip out of the thread loops 11b, 13b. As the needles 19, 21 rise and the fabric is sent forward by the length of one seam, the thread loops 11b, 13b are absorbed into a newly formed seam, and tightened and stretched straightway on the fabric, thereby forming a neat seam without crease (Fig. 7).

[0026] When forming a thread chain consecutive to the sewing end after sewing a fabric, the thread adjusting device 33a is changed over to be inactive and the thread adjusting device 33b to be active by means of the changeover device. The formed thread chain does not fall down as the needle threads 11, 13 are supported by the thread support 27 on the presser foot 23 as shown in Fig. 8. When the tension of the right needle thread 11 is set low and the tension of the looper thread 15 to be high, for example, by the thread adjusting device 33b, the loop 11a of the right needle thread 11 is pulled toward the loop 13a of the left needle thread 13 by the looper thread 15, and the thread loops by the right and left needle threads are put together into one thread chain and sent out smoothly. To send out the thread chain securely, the thread chain may be sent out by installing a feed dog of the same type as the feed dog 31 for sending out the fabric at a position corresponding to the rear part of the presser foot 23.

[0027] The thread support in the foregoing embodiment prevents puckers or waves by mutual pulling of the seam rows, and therefore it is provided at the same height or above the presser foot for holding the thread chain, but when it is intended to hold the thread chain only, it may be provided on or beneath the needle plate.

[0028] The foregoing embodiment relates to the double chain stitch sewing machine with two needles, but by using the same thread support in a sewing machine with one needle or three needles or in a lock stitch sewing machine or other sewing machines, formation of puckers or waves due to mutual pulling of seam rows may be prevented, and in a sewing machine provided with a looper, the thread chain can be formed securely.

[0029] In this embodiment, the thread support moves only reciprocally, but it may be also designed to approach the needle thread from before the needle along with the elevation of the needle and move in the lateral direction when setting aside.

Claims

1. A sewing method for sewing a fabric with a sewing machine comprising a vertically moving needle (19, 21), a thread loop taker (35) disposed beneath a needle plate (29) for forming a seam in cooperation with the needle, and a fabric feed device (31), said sewing method comprising steps of supporting a needle thread (11b, 13b) consecutive from the seam to the needle (19, 21) by a thread support means (27) traversing on a fabric delivery side of the needle when the needle descends in order to form a next seam, and putting aside the thread support means (27) when the needle rises.

2. A sewing method of claim 1, wherein said sewing machine comprises a plurality of vertically moving needles and a single thread loop taker disposed beneath said needle plate for forming a seam in cooperation with said needles.

3. A sewing method of claim 1, wherein said sewing machine comprises a plurality of vertically moving needles and a single looper traveling in a direction of arrangement of said needles beneath said needle plate to form a seam in cooperation with said needles.

4. A sewing method of claim 3, wherein the needles are composed of a right needle and a left needle, and when forming a thread chain, a thread tension of the right needle thread is set low and a thread tension of the looper thread is high.

5. In a sewing machine comprising one or more vertically moving needles (19, 21), a thread loop taker (35) disposed beneath a needle plate (29) for forming a seam in cooperation with the needles (19, 21), and a fabric feed device (31), said sewing machine further comprising a thread support means (27) which traverses a rear side of said needles (19, 21) when said needles (19, 21) descend, and moves in synchronism with a vertical movement of said needles (19, 21) so as to set aside when said needles (19, 21) rise.

6. In a sewing machine comprising a plurality of vertically moving needles (19, 21), a single looper (35) traveling in a direction of arrangement of said needles beneath a needle plate (29) to form a seam in cooperation with the needles (19, 21), and a fabric feed device (31), said sewing machine further comprising a thread support means (27) for traversing a rear side of the needles (19, 21) when the needles (19, 21) descend, and moving in synchronism with the vertical movement of the needles (19, 21) so as to set aside when the needles rise.

7. A sewing machine of claim 5 or 6, wherein the needle support means is disposed at the same or higher level than the level of a presser foot of the sewing machine.

8. A sewing machine of claim 6, wherein the thread support means is disposed on the needle plate or beneath it.

9. A sewing machine of claim 6, wherein the fabric feed device comprises a presser foot, a first feed dog set under the presser foot oppositely, and a second feed dog for delivering a thread chain acting in synchronism with the first feed dog.

Drawing