Thread chain and method and apparatus for drawing out the thread chain on multiple needle sewing machines

Abstract: A sewing machine possessing multiple needles and a single looper for forming a double chain stitch without an upper covering thread capable of drawing out a thread chain reliably and smoothly. By an auxiliary blade 21 disposed parallel to a looper 4, the thread chain C consecutive to the looper 4 is supported, thereby preventing the thread chain from being pushed down beneath a throat plate 3 with the descending needles 1, 2. On the throat plate 3, a stitch formation tongue composed of a movable slender plate 19 is provided, and this tongue is withdrawn when making the thread chain. The sewing machine is provided with tension regulator groups for sewing and regulator for forming thread chain respectively. In the tension regulator group for forming thread chain, the tension of the right needle thread 9 is set smaller than the tension of the looper thread 11. By a rear feed dog 16, the thread chain C is drawn out through a guide groove 18 at the left rear end of a needle hole 13 toward the middle of said feed dog 16.

Description: BACKGROUND OF THE INVENTION Field of the Invention The invention relates to a method and apparatus for drawing out a thread chain reliably and smoothly on a sewing machine of the type which forms multiple-needle stitches (U.S. Federal Standard stitch type 406 or 407) by at least two needles and one looper, and a novel thread chain that can be formed by the sewing machine of such type. Description of the Prior Art In a sewing machine of the type which forms stitches by using multiple needles and one looper, such as the multiple-needle, double chain stitch sewing machine without using upper cover thread, it is important to form a thread chain smoothly between consecutive fabrics in order to feed the fabrics one after another and sew intermittently by continuously operating the sewing machine. In a conventional sewing machine of the above type, however, after sewing one fabric, the thread chain linked to the sewing end is pushed down beneath the throat plate as the needles descend, and therefore, in in the next step, when the looper goes out to pick up the needle thread loop, it simultaneously hooks up the pressed-down thread chain, and the thread chain cannot be delivered, and moreover the right and left needle threads cannot maintain a specific interval unless there is a fabric for sewing, and are hence unable to form uniform stitches, thereby making it impossible to draw out and deliver the thread chain onto the throat plate by holding it with the feed dog behind the feeding direction of the stitch making zone, so that the thread chain cannot be made reliably. Accordingly, hitherto, in this kind of sewing machine, when the fabric reached the sewing end, the machine was stopped and the threads were trimmed, and after removing the sewn fabric, the starting end of a next fabric was fed on the throat plate beneath the presser foot, and the presser foot was lowered to resume sewing operation, and therefore it was impossible to sew by feeding the fabrics one after another by operating the sewing machine continuously. In this kind of sewing machine, it is also proposed to form a thread chain by the sewing machine. An example is disclosed in the Japanese unexamined patent publication number 3-23887 (U.S. Patent 5,027,728), in which a thread brake device is projected at the lower side of the stitch formation tongue formed by the portal needle hole of the throat plate, and at the end of sewing the same stitch as the one formed on the fabric is formed on the thread brake device to hold the thread chain to prevent descent of the thread chain due to lowering of the needles, and the formed thread chain is delivered by a rear feed dog disposed in its feed direction to make the thread chain. Another sewing machine for forming a thread chain is proposed in the Japanese patent publication number 57-58191 (U.S. Patent 4,186,676), in which the thread tension of the right one of the two needles is set free at the end of sewing, and the right needle thread does not resist the force of attraction toward the left needle thread by the looper thread, and the thread chain is sent out by the rear feed dog and auxiliary feed member disposed at the delivery side of the needle hole. SUMMARY OF THE INVENTION It is hence a primary object of the invention to provide a method and apparatus for drawing out the thread chain more stably and smoothly than the conventional sewing machines described above, and more particularly to provide a thread chain, hardly unraveled and uniform in balance, that can be formed by the aforesaid multiple-needle sewing machine. According to a first aspect of the invention a method is provided for drawing out a thread chain in a sewing machine for forming a double chain stitch without upper cover thread by co-operation of at least two threads supplied by separate needles and one looper thread looped via a looper, characterised in that said method comprises the steps of: changing over the tension of one of the needle threads to low and the tension of the looper thread to high when sewing of fabric is finished, supporting the thread chain consecutive or adjacent to the looper by an auxiliary blade disposed parallel to the looper, and drawing and sending the thread chain onto a throat plate by a rear feed dog disposed backward of a needle hole of the throat plate. According to a second aspect of the invention an apparatus is provided for drawing out a thread chain in a sewing machine for forming a double chain stitch without upper cover thread by co-operation of at least two needles operating on needle threads and one looper operating on a looper thread, and comprising a throat plate having a needle hole formed in portal shape around a stitch formation tongue, characterised in that said apparatus comprises: an auxiliary blade disposed parallel to and attached on the looper for preventing the thread chain from falling when the needles descend by supporting the thread chain consecutive or adjacent to the looper, a rear feed dog (16) for sending out the thread chain disposed at the delivery side of the needle hole and tension changeover means for changing over the tension of the one needle thread to low and the tension of the looper thread to high. It is one of the features of the invention that the thread chain is prevented from being hooked by the looper as it is pushed down by the descending needle and dropped beneath the throat plate, by supporting the thread chain consecutive to the looper by an auxiliary blade disposed parallel to the looper and arranged to make elliptical motions back and forth, and right and left, together with the looper. Besides, the formed thread chain is led into the middle of the rear feed dog through a guide groove formed on the throat plate upper surface, and is sent out backward on the needle plate by the feed action of the rear feed dog. The tongue formed by the portal needle hole of the throat plate is preferably retractable, and retreats to withdraw forward at the end of sewing. Hence, the right and left needle threads approach to each other to assemble into one body, thereby delivering smoothly. It is another feature of the invention to support a thread chain consecutive to the looper by thread chain supporting means such as said auxiliary blade and change over the tension of one of the two needle threads to small and the tension of the looper thread to large at the end of sewing. By the tension changeover, the needle thread of the smaller tension is shifted to the other needle thread side of the larger tension to form a thread chain as one uniform string, so that the delivery of the thread chain by the rear feed dog may be smooth. In this case, too, the tongue is retractable, and it is preferred so that it may withdraw from the needle hole at the end of sewing so as not to interfere the shift of the needle thread. In the present invention, too, it is desired to form a guide groove on the throat plate upper surface so that the formed thread chain may be led to the middle of the rear feed dog through the guide groove. In this case, the guide groove is formed toward the middle of the rear feed dog from the needle hole of the side to which the needle thread is shifted. As the tension changeover means, tension regulators are divided into two groups. One of the two groups has three tension regulators for sewing the fabric for properly setting the tension of two needle threads and one looper thread, and another group has three tension regulators for forming thread chain, and when sewing the fabric, the tension regulators of the latter group are released, and the tension is applied by the tension regulators of the former group, and when forming the thread chain at the end of sewing, to the contrary, the tension regulators of the former group are released, and the tension regulators of the latter group are used, thereby changing over the two groups. The straight inside edge, which extends from the needle penetrating path with large diameter to the end of the tongue, of the needle hole formed in a portal shape in the throat plate allows the needle thread to slip out smoothly from the needle penetrating path without being caught when the needle thread tension is relaxed. The thread chain of the present invention may consist of a first needle thread alternately repeating open loops of peak and bottom in a corrugated form, a second needle thread continuously repeating closed loops parallel to the first needle thread and a looper thread continuously repeating open loops for linking the first and second needle threads so that the n-th open loop of the looper thread passes through the inside ground of the bottom of the m-th open loop of the first needle thread by passing through the inside of the closed loop of the second needle thread, and further the end of n-th open loop of the looper thread winds around the upper outside of the bottom of the m+1-th open loop of the first needle thread and n+1-th open loop of the looper thread passes through the ground of the bottom of the m+1-th open loop of the first needle thread by passing through the inside of the next closed loop of the second needle thread. The thread chain of the present invention is hardly unraveled and uniform in balance because of the thread entangling. Other features and advantages of this invention will be clearly understood from the appended description referring by way of a non-limiting example to an embodiment shown on the accompanying figures of drawing wherein: BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view showing a mode of drawing out a thread chain. Fig. 2 is a plan view of a needle hole formed in a portal shape on a throat plate. Fig. 3 is a partial perspective view of a flat sewing machine. Fig. 4 is a partial perspective view of another throat plate. Fig. 5 is a plan view showing the sewing state when the front end of a slender plate projects into the needle hole. Fig. 6 is a plan view showing the state of forming a thread chain as the front end of the slender plate retreats and withdraws from within the needle hole. Fig. 7 is a front view of a looper mounting an auxiliary blade. Fig. 8 is a plan view of the looper shown in Fig. 7. Fig. 9 is a perspective view showing stitches at the time of sewing, without showing the fabric to be sewn. Fig. 10 is a perspective view showing a process for forming a thread chain. Fig. 11 is a perspective view showing the state of retreat of the looper as the needle reaches the bottom end point when forming a thread chain. DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 3 partially shows the flat sewing machine for forming a double-chain stitch with a lower cover thread (JIS B 9070 D23A, i.e. U.S. Federal Standard stitch type 406) by cooperation with a left needle 1, a right needle 2, and a looper 4 beneath the throat plate 3, wherein tensioning means composed of tension regulators 5, 5' for left needle thread 8, tension regulators 6, 6' for right needle thread 9, and tension regulators 7, 7' for looper thread 11 are disposed parallel in two rows A, B on the stand (not shown) rising from the bed. The tension device of the first row A is composed of tension regulators 5, 6, 7 and the tension regulators 5 and 6 are designed to provide the needle threads 8 and 9 with a tension suited for sewing, while the tension regulator 7 is set so as to provide the looper thread 11 with a weak tension suited for sewing. The tension device of the second row B is composed of tension regulator 5', 6', 7' and used for forming a thread chain C, and the tension regulator 5' provides the needle thread 8 with a proper tension same as when forming a stitch, the tension regulator 6' provides the needle thread 9 with a weak tension, and the tension regulator 7' is set to provide the looper thread 11 with a strong tension. The tension devices of the both rows A, B are respectively equipped with thread loosening plates 10, 10', and by moving them the tension devices are changed over to release one side when using the other one. That is, when forming a stitch on the fabric, the tension device of the first row A is used, while the tension device of the second row B is released, but when the sensor (not shown) for detecting the passing of the fabric end through the needle location detects the fabric end, the tension devices are changed over, and the tension device of the first row A is released while the tension device of the second row B is closed, so that the threads are provided with the tension of this tension device of the second row B. The throat plate 3 comprises, as specifically shown in Fig. 4 through Fig. 6, a rectangular needle hole 13, two penetration holes 15 having feed dogs 14 disposed at both sides of the needle hole 13, a penetration hole 17 having a rear feed dog 16 for drawing the thread chain C disposed at the delivery side of the cloth feed direction of the needle hole 13, a V-shaped guide groove 18 extending toward the middle of the penetration hole 17 from the left side of the needle hole 13, and a slender plate 19 installed slidably back and forth on the throat plate 3, with the end projecting rectractably in the needle hole 13, and having the front end functioning as the stitch formation tongue in the projected state (Fig. 5). For forming the thread chain C, the slender plate 19 goes back to retract the front end from the needle hole 13 when the cloth sensor detects the rear end of cloth (Fig. 6). This slender plate 19 is parallel and straight on both side edges 19a, and will not hook the thread chain C when going back and forth. Besides, in another case as shown in Fig. 2, when provided with a stitch formation tongue T stationarily in the needle hole 13' of the throat plate 3', the thread chain C is drawn out smoothly by forming straightly the edge Ta from the right side needle drop portion b to the front end of the tongue T. Incidentally, as the means for changeover of tension devices A, B and forward and backward motion of the slender plate 19, known driving means may be used, such as a solenoid or air cylinder. The looper 4 has an auxiliary blade 21 provided in parallel and apart to its back side as shown in Figs. 1, 7 and 8, and the front end of the auxiliary blade 21 is projected ahead of the front end of the looper 4 by the length of the oscillating stroke of the looper 4. The sewing machine of the embodiment is constituted in this way, and when sewing, the front end of the slender plate 19 is projected into the needle hole 13 (Fig. 5), and the tension device of the row B for thread chain C in Fig. 3 is released, and the sewing is effected in the state of providing the needle threads 8, 9 and looper thread 11 with tension by the tension device of the row A for sewing. Fig. 9 shows the U.S. Federal Standard stitch type 406 formed in this operation. After sewing, when the fabric rear end goes out of the cloth sensor and it is detected by the sensor, the slender plate 19 goes back, and its front end is withdrawn from the needle hole 13, and the tension devices are changed over, and the tension device of the row A for sewing is released, and the tension is applied to the threads by the tension device of the row B for the thread chain C. That is, the tension of the left needle thread 8 is unchanged, and the tension of the right needle thread 9 is changed to small and the tension of the looper thread 11 to large, so that the right needle thread 9 with the smaller tension is pulled by the looper thread 11 and shifted to the left needle thread 8 side. As a result, the left needle 1 is, same as in the case of sewing, placed within the triangle formed by the looper 4, the loop of the needle thread 8 hooked on the looper 4, and the looper thread 11, while the right needle 2 falls outside (the right side in Fig. 10) of the loop of the needle thread 9 applied on the looper 4, and since the right needle thread 9 is weak in tension and is inverted, being overcome by the tension of the looper thread 11, thereby repeating the closed loop 9a continuously. The loop 11a of the looper thread passing through the closed loop 9a passes through each loop 8a of the needle thread 8, and forms the thread chain C in a form of enclosing the loop 8a just before it. The thread chain C thus formed is shifted to the loop 8a side of the needle thread 8, without being interfered by the front end of the slender plate 19 in the needle hole 13, by the looper thread 11 of which tension is intensified by the loop 9a of the needle thread 9 reduced in tension, thereby forming one string, which passes through the guide groove 18 in the state of being supported by the auxiliary blade 21, and is led toward the middle of the rear feed dog 16, and is drawn out by the rear feed dog 16. The front end of the auxiliary blade 21 is extended ahead of the looper 4 and is always at the left side of the left needle 8, and holds the thread chain C until the looper 4 goes back and the needles 1, 2 reach the bottom end point (Fig. 11), thereby preventing its descent. Hence, if the looper 4 moves forward, it will not hook the thread chain C.

Claims: A method for drawing out a thread chain (c) in a sewing machine for forming a double chain stitch without upper cover thread by co-operation of at least two threads (8,9) supplied by separate needles (1,2) and one looper thread (11) looped via a looper (4), characterised in that said method comprises the steps of: changing over the tension of one of the needle threads (8,9) to low and the tension of the looper thread (11) to high when sewing of fabric is finished, supporting the thread chain (c) consecutive or adjacent to the looper (4) by an auxiliary blade (21) disposed parallel to the looper (4), and drawing and sending the thread chain (c) onto a throat plate (3) by a rear feed dog (16) disposed backward of a needle hole (13) of the throat plate (3). The method for drawing out a thread chain (c) according to Claim 1, said method further comprising a step of leading the thread chain (c) toward the middle of the rear feed dog (16) through a guide groove (18) which is formed on the throat plate (3). The method for drawing out a thread chain (c) according to Claim 1 or 2, said method further comprising a step of withdrawing a stitch formation tongue (19,T) from the needle hole (13) when sewing of fabric is finished, the stitch formation tongue (19, T) being disposed in the throat plate (3) retractably to project into the needle hole (13). An apparatus for drawing out a thread chain (c) in a sewing machine for forming a double chain stitch without upper cover thread by co-operation of at least two needles (1, 2) operating on needle threads (8, 9) and one looper (4) operating on a looper thread (11), and comprising a throat plate (3) having a needle hole (13) formed in portal shape around a stitch formation tongue (T, 19), characterised in that said apparatus comprises: an auxiliary blade (21) disposed parallel to and attached on the looper (4) for preventing the thread chain (c) from falling when the needles (1, 2) descend by supporting the thread chain (c) consecutive or adjacent to the looper (4), a rear feed dog (16) for sending out the thread chain (c) disposed at the delivery side of the needle hole (13), and tension changeover means (10, 10') for changing over the tension of the one needle thread (8, or 9) to low and the tension of the looper thread (11) to high. The apparatus for drawing out a thread chain (c) according to Claim 4, wherein said needle hole (13) is rectangular in shape in which the stitch formation tongue (T,19) retractably projects to form the rectangular needle hole in a portal shape. The apparatus for drawing out a thread chain (c) according to Claim 5, wherein said needle hole (13) is shaped so that at least one of the right and left needle penetrating paths of large diameter is formed without a step at an inner edge of said needle hole. The apparatus for drawing out a thread chain (c) according to Claim 4, said apparatus further comprising a guide groove (18) for the thread chain (c) extending from the left biased side of the needle hole (13) toward the middle of the rear feed dog (16), the guide groove (18) being formed on the throat plate (3). A thread chain formed by a multiple-needle sewing machine comprising a first needle thread (8) alternately repeating open loops (8a) of peak and bottom in a corrugated form, a second needle thread (9) continuously repeating closed loops (9a) parallel to the first needle thread (8), and a looper thread (11) continuously repeating open loops for linking the first and second needle threads (8, 9), so that the n-th open loop of the looper thread (11) passes through the inside ground of the bottom of the m-th open loop of the first needle thread (8) by passing through the inside of the closed loop of the second needle thread, and further the end of n-th open loop of the looper thread winds around the upper outside of the bottom of the m+1-th open loop of the first needle thread (8), and n+1-th open loop of the looper thread passes through the ground of the bottom of the m+1-th open loop of the first needle thread by passing through the inside of the next closed loop of the second needle thread.

Inventors: NISHIKAWA MASAHIKO, NISHIKAWA, MASAHIKO, Nishikawa, Masahiko, c/o Pegasus Sewing Machine
Applicants: PEGASUS SEWING MACHINE MFG CO, PEGASUS SEWING MACHINE MFG. CO., LTD.
Application year: 1993
Main classification: D05B65
IPC codes: D05B57, D05B61, D05B65, D05B73, D05B1