Apparatus for preventing stitching from raveling

Abstract: The present invention relates to an apparatus for preventing a double chain stitching from raveling. Looper thread engaging means engages with the looper thread consecutive to the looper from the cloth by moving when the looper is at the forward position and forms a looper thread loop consecutive from the cloth at the engaged portion by driving a sewing machine in said engaged state. A looper thread cutter cuts the looper thread loop at the engaged portion and a thread cutter cuts the loop-shaped needle thread consecutive to the needle via the looper from the cloth and the looper thread consecutive to the looper from the cloth between the cloth and the looper. Therefore, it is able to prevent that a double chain stitching ravels from said stitching end side. Further, defining means is provided to define the moving distance of the looper thread engaging means. The length of the looper thread loop is changed by definition of moving distance of the looper thread engaging means by the defining means. Therefore, the length of the thread end left over in the cloth by the looper thread cutter can be varied. By varying the length of thread end consecutive to the sewn end side, a good-looking sewn product is obtained.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for preventing a stitching from raveling from the sewn end side on forming a double chain stitch in a cloth by a sewing machine. 2. Description of the Prior Art This kind of stitching ravel preventing device is used in a sewing machine having at least one needle moving vertically, and a looper oscillating almost horizontally between the forward position and backward position across the needle, in which the double chain stitch is formed in the cloth after a thread triangle is formed by a loop-shaped needle thread consecutive to the needle via the looper from the cloth and a looper thread along the looper via the looper eyelet from the cloth by collaboration of the needle and looper. By this sewing machine, when a stitch, for example, JIS L0120 stitch type 406, is formed, if the looper thread is pulled from the sewn end side of the stitching, the stitching is raveled out. As an apparatus for preventing a stitching from raveling, it is disclosed in Japanese Laid-open Patent No. 9-225163 that the constitution comprises such sewing machine, looper thread engaging means, a looper thread cutter and a thread cutter. Looper thread engaging means forms a looper thread loop consecutively from the cloth at the engaged portion by driving the sewing machine in a state engaged with the looper thread consecutive to the looper from the cloth by moving when the looper is located at the forward position. The looper thread cutter cuts off the looper thread loop at said engaged portion. The thread cutter cuts off the loop-shaped needle thread consecutive to the needle via the looper from the cloth and the looper thread consecutive to the looper from the cloth between the cloth and the looper. According to such constitution, at nearing the sewing finish on the double chain stitch formed in the cloth, it makes the looper thread engaging means engage with the looper thread consecutive to the looper from the cloth. In this state, the sewing machine is driven for one stitch, and the looper thread loop consecutive from the cloth is formed at the engaged portion, and then the looper thread loop at the engaged portion is cut off, and afterward or at the same time the loop-shaped needle thread consecutive to the needle through the looper from the cloth and the looper thread consecutive to the looper from the cloth are cut off between the cloth and the looper. In such conventional ravel preventing method, however, since the moving distance of the looper thread engaging means cannot be defined, the length of the looper thread loop formed by the looper thread engaging means cannot be changed, and therefore the length of the thread end left over in the cloth by the looper thread cutter could not be changed. SUMMARY OF THE INVENTION The present invention is devised in the light of the above-mentioned background, and it is hence an object of the present invention to provide an apparatus capable of preventing a stitching from raveling from the sewn end side on forming a double chain stitch in a cloth by a sewing machine, and obtaining a good-looking sewn product by varying the length of thread end consecutive to the sewn end side. To achieve the object, the apparatus for preventing a stitching from raveling of the present invention comprises a sewing machine having at least one needle (5, 6) moving vertically and a looper (3) for forming a double chain stitch (S) made up of needle threads (8, 9) and looper thread (10) in a cloth (W) by collaboration with the needle by oscillating almost horizontally between the forward position and backward position across the needle (5, 6), looper thread engaging means (11) for forming a looper thread loop (10L) consecutive from the cloth (W) at its engaged portion by driving the sewing machine in an engaged state by engaging with the looper thread (10) consecutive to the looper (3) from the cloth (W) by moving when the looper (3) is at the forward position, a looper thread cutter (12) for cutting the looper thread loop (10L) at the engaged portion, and a thread cutter (30) for cutting loop-shaped needle threads (8L, 9L) consecutive to the needles (5, 6) via the looper (3) from the cloth (W) and the looper thread (10) consecutive to the looper (3) from the cloth (W) between the cloth (W) and the looper (3), in which defining means (27) is further provided to define the moving distance of the looper thread engaging means (11), and the length of the looper thread loop (10L) is changed by definition of moving distance of the looper thread engaging means (11) by the defining means (27), and therefore the length of the thread end left over in the cloth (W) by the looper thread cutter (12) can be varied. According to the present invention having the above-mentioned characteristic constitution, when the looper is at the forward position near the sewing finish on the double chain stitch formed in the cloth by the swing machine, the looper thread engaging means is moved and is engaged with the looper thread consecutive to the looper from the cloth. The moving distance of the looper thread engaging means is defined by the defining means. In this engaged state, by driving the sewing machine, a looper thread loop consecutive from the cloth is formed at the engaged portion of the looper thread engaging means. The length of the looper thread loop is defined by changing the engaged state with the looper thread engaging means by the defining means. The looper thread loop at the engaged portion by the looper thread engaging means is cut off by the looper thread cutter, and the loop-shaped needle thread consecutive to the needle via the looper from the cloth and the looper thread consecutive to the looper from the cloth are cut off by the thread cutter between the cloth and the looper. As a result, the length of the thread end left over in the cloth by the looper thread cutter can be changed, and a good-looking sewn product is obtained. In said apparatus having such constitution, the looper thread engaging means includes at least a looper thread engaging member and a driving member for moving the looper thread engaging member to the engagement position of the looper thread, and the defining means is composed of a stopper piece for defining the moving distance of the driving member. When the looper thread engaging member is moved by the driving member and is engaged with the looper thread consecutive to the looper from the cloth, its moving distance is defined by the stopper piece. Also in said apparatus having such constitution, the looper thread engaging member has a taper portion and two crooks protruding nearly at the middle position and tip position of the taper portion. When a position of the looper thread engagement with the taper portion across the crook at the middle position can be changed depending on the definition of the moving distance of the driving member by the stopper piece, the crook can be easily engaged with the looper thread consecutive to the looper from the cloth. In addition, the looper thread loop can be cut off by the looper thread cutter securely at the corresponding crook. Moreover, said stopper piece is a rectangular block fixed in the sewing machine so as to be variable in angle and the definition of the moving distance in the driving member is done by varying the fixing angle of the rectangular block in the sewing machine, the moving distance of the driving member can be defined in a simple constitution. Other objets and effects of the present invention will be better understood from the following detailed description of the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an essential perspective view of an embodiment of an apparatus for preventing a stitching from raveling of the present invention. Fig. 2 is an essential magnified side view of said apparatus. Fig. 3 is an essential magnified front view of said apparatus. Fig. 4 is a schematic perspective view showing a first step at sewing finish on a double chain stitch in the embodiment of said apparatus. Fig. 5 is a schematic perspective view showing a second step at sewing finish on a double chain stitch. Fig. 6 is a schematic perspective view showing a third step at sewing finish on a double chain stitch. Fig. 7 is a schematic perspective view showing a fourth step at sewing finish on a double chain stitch. Fig. 8 is a schematic perspective view showing a fifth step at sewing finish on a double chain stitch. Fig. 9 is a schematic perspective view showing a first step at sewing finish on a double chain stitch when the moving distance is defined. Fig. 10 is a schematic perspective view showing a second step at sewing finish on a double chain stitch when the moving distance is defined. Fig. 11 is a schematic perspective view showing a third step at sewing finish on a double chain stitch when the moving distance is defined. Fig. 12 is an essential magnified side view showing other embodiment of an apparatus for preventing a stitching from raveling. Fig. 13 is an essential magnified schematic plan view showing the other embodiment of an apparatus for preventing a stitching from raveling. Fig. 14 is an essential magnified schematic plan view showing another embodiment of an apparatus for preventing a stitching from raveling. PREFERRED EMBODIMENTS OF THE INVENTION A preferred embodiment of the present invention is described below while referring to the accompanying drawings. Fig. 1 is a perspective view of essential parts of a sewing machine in which an apparatus for preventing a stitching from raveling of the invention is incorporated. A cylinder bed 1 of this sewing machine has a feed dog 2 for feeding a cloth W in a direction of arrow F by moving vertically and longitudinally, a looper 3 for oscillating back and forth in a direction crossing with the cloth feed direction F, and a throat plate (not shown) fixed in a screw hole 4. Above the cylinder bed 1, a needle bar 7 having a left needle 5 and a right needle 6 is provided. By the vertical motion of this needle bar 7, the tip ends of the needles 5, 6 penetrate into needle holes (not shown) in a throat plate. The looper 3 oscillates almost horizontally on an elliptical orbit between the forward position and backward position across the tip ends of the needles 5, 6 penetrating through the needle holes in the throat plate. As shown in Fig. 4 through Fig. 11, the tip ends of the needles 5, 6 are provided with thread holes 5a, 6a for inserting needle threads 8, 9, and a blade 3b of the looper 3 has an eyelet 3a for inserting a looper thread 10. By the collaboration of the needles 5, 6 threaded the needle threads 8, 9 in the thread holes 5a, 6a, and the looper 3 threaded the looper thread 10 in the eyelet 3a, as shown in Fig. 4 and Fig. 5, a thread triangle is formed of loop-shaped needle threads 8L, 9L consecutive to the needles 5, 6 via the blade 3b of the looper 3 from the cloth W and the looper thread 10 along the looper 3 via the eyelet 3a from the cloth W. Thereafter, as shown in Fig. 6, the needle thread loops 8L2, 9L2 which the looper 3 is detached from the loop-shaped needle threads 8L, 9L are pulled up to the cloth W, so that a double chain stitch S is formed in the cloth W. At the left side of the feed dog 2 in Fig. 1, that is, at the tip end portion of the cylinder bed 1, there are looper thread engaging means 11 for forming a looper thread loop 10L consecutive from the cloth W at its engaged portion by driving the sewing machine in an engaged state by engaging with the looper thread 10 consecutive to the looper 3 from the cloth W by moving, and a looper thread cutter 12 for cutting off the looper thread loop 10L at said engaged portion. The looper thread engaging means 11 includes a looper thread engaging member 14 mounted on the cylinder bed 1 rotatably (movably) by means of a stepped screw 13, and a driving member 15 for rotating (moving) the looper thread engaging member 14. The looper thread engaging member 14 has a crook lever 16 at one side, and a slot 17 is formed at other side. The tip end of the crook lever 16 has, as most clearly shown in Fig. 5 through Fig. 7, a taper portion 16c, and two crooks 16a, 16b protruding at the middle position and leading end position of the taper 3 portion 16c, respectively. The base end portion of the crook lever 16 is adjustably fixed to a position on the looper thread engaging member 14 through a slot 18 and a screw 19. The driving member 15 is disposed at the tip end of the cylinder bed 1, and comprises a pneumatic cylinder 21 in which air is supplied from a high pressure air source (not shown) through a tube 20, a pi-shaped working piece 23 (see Fig. 2) fixed adjustably to a position on a piston rod 21a of the pneumatic cylinder 21 through a screw 22, and a stepped screw 24 coupled to the looper thread engaging member 14 through the slot 17 on the upper surface of the working piece 23. By the pneumatic force supplied from the high pressure air source, the working piece 23 fixed on the piston rod 21a is forced to move back and forth in the direction of arrow A shown in Fig. 1 and Fig. 2. By the forward and backward motion of the working piece 23, the crook lever 16 of the looper thread engaging member 14 is forced to rotate (move) about the stepped screw 13 in the direction of arrow B. The looper thread cutter 12 is fixed on a bracket 25 fixed on the cylinder bed 1 by means of a screw 25a, and is disposed along the lower surface of the throat plate. The looper thread cutter 12 is provided with a push spring 26. This push spring 26 is provided beneath the bracket 25, and pushes the crook lever 16 of the looper thread engaging member 14 to the looper thread cutter 12. The center of the bracket 25 is dented so as not to interfere with the crook lever 16 rotating about the stepped screw 13. At the tip end of the cylinder bed 1, there is defining means 27 for defining the rotating angle (moving distance) of the looper thread engaging member 14. This defining means 27 is a stopper piece composed of a rectangular block fixed angle-adjustably to the tip end wall 1a of the cylinder bed 1 through a screw 28. This stopper piece 27 of rectangular block has a screw hole 28a provided at a lower position from the center of gravity of the rectangular shape in this block. By loosening the screw 28, the entire stopper piece 27 can be changed in angle about the screw hole 28a. When the stopper piece 27 is positioned in the moving range of the working piece 23 in the driving member 15 as indicated by single dot chain line in Fig. 2 and Fig. 3, the working piece 23 is designed so as to define its moving distance. At the right side of the feed dog 2 in Fig. 1, that is, at the base end portion of the cylinder bed 1 of the sewing machine, there is a thread cutter 30 for cutting off the needle threads 8, 9 consecutive to the needles 5, 6 via the looper 3 from the cloth W and the looper thread 10 consecutive to the looper 3 from the cloth W between the cloth W and the looper 3 by the forward and backward move of a hook 29. The hook 29 is driven by a well-known driving device (not shown), and moves back and forth between the forward position and backward position along the upper side of the blade 3b of the looper 3. The thread cutter 30 has a fixed knife 32 and a push spring 33. The hook 29 is pressed to the fixed knife 32 by the push spring 33, and cuts off the thread in collaboration with the fixed knife 32 at the backward position. In the apparatus for preventing a stitching from raveling having above-mentioned constitution, the ravel preventing operation at sewing finish is explained by reference to Fig. 4 through Fig. 11. As shown in Fig. 4, the cloth W is fed in the direction of arrow F by the feed dog 2 of the sewing machine. In the fed cloth W, a double chain stitch S of stitch type 406 is formed by the needle threads 8, 9 and looper thread 10 respectively threaded to the needles 5, 6 and looper 3 As nearing the finish of the stitch forming in the cloth W, as shown in Fig. 4, when the needles 5, 6 are nearly at the upper dead point and the looper 3 is close to the forward position, the pneumatic cylinder 21 is operating by the pneumatic force from the high pressure air source, and the looper thread engaging member 14 is rotated in the clockwise direction about the stepped screw 13. By rotation of the looper thread engaging member 14, the crook lever 16 moves above the blade 3b of the looper 3 so as to cross it along the nearly opposite direction of the cloth feed direction F. By this crossing motion, as shown in Fig. 5, the tip end of the crook lever 16 is inserted into the thread triangle, and the taper portion 16c formed at the base end side of the crook lever 16 from the crook 16b at the middle position is engaged with the looper thread 10 consecutive to the looper 3 from the cloth W. Herein, if the stopper piece 27 is positioned in the moving range of the working piece 23 in the driving member 15, the moving distance of the working piece 23 is defined. Therefore, as shown in Fig. 9, the degree of engagement of the crook lever 16 with the looper thread 10 is changed and becomes shallow. That is, the taper portion 16c formed between the crook 16a and the crook 16b is engaged with the looper thread 10 consecutive to the looper 3 from the cloth W. In succession, as shown in Fig. 6, the needles 5, 6 descend into the thread triangle, and the looper 3 moves back to the backward position through the front side of the needles 5, 6. At this time, by the needle thread loops 8L2, 9L2 detached from the looper 3, the looper thread engaged with the taper portion 16c (engaged portion) of the crook lever 16 is pulled up to the cloth W, so that the looper thread loop 10L consecutive to the cloth W is formed. When the stopper piece 27 is positioned outside of the moving range of the working piece 23 in the driving member 15, the looper thread loop 10L engaged with the taper portion 16c is in a state as shown in Fig. 6, and when the stopper piece 27 is positioned in said moving range, the looper thread loop 10L engaged with the taper portion 16c is in a state as shown in Fig. 10. That is, when the moving distance of the looper thread engaging member 14 is defined by the stopper piece 27, as compared with the case not defined, the looper thread loop 10L held by the taper portion 16c is shorter. While the looper 3 moving forward through the backward position passes the back side of the needles 5, 6, said looper 3 captures a needle thread loop newly formed by the needles 5, 6 ascending from the lower dead point, and new loop-shaped needle threads 8LL, 9LL are formed. That is, Fig. 7 shows a state of driving the sewing machine for one stitch from the state in Fig. 5, and Fig. 11 shows a state of driving the sewing machine by one stitch from the state in Fig. 9. In either case, the looper thread loop 10L engaged with the taper portion 16c of the crook lever 16 keeps its state slightly above the looper 3. At this time, by suspension of pneumatic pressure from the high pressure air source, the pneumatic cylinder 21 is operated, and the looper thread engaging member 14 is rotated in the counterclockwise direction about the stepped screw 13. By the rotation of the looper thread engaging member 14, the looper thread loop 10L engaged with the taper portion 16c is transferred to engagement of the crook 16b, (in the case from the state shown in Fig. 11, the looper thread loop 10L is transferred to engagement of crook 16a,) and then the looper thread loop 10L at the engaged portion is cut off beneath the looper thread cutter 12. In this way, the both thread ends 10f, 10e cut off by the looper thread cutter 12 hang from the cloth W side, and the length of the thread ends 10f, 10e is varied depending on the length of the looper thread loop 10L engaged with the taper portion 16c. At cutting off the looper thread loop 10L, by driving the driving device not shown, the hook 29 moves back and forth between the forward position and backward position along the upper side of the blade 3b of the looper 3. The hook 29 moving backward from the forward position to the backward position is engaged with the looper thread 10 consecutive to the looper 3 from the cloth W, and new loop-shaped needle threads 8LL, 9LL consecutive to the needles via the looper 3 from the cloth W. By collaboration with the fixed knife 32, the looper thread 10 and the new loop-shaped threads 8LL, 9LL engaged with the hook 29 are cut off between the cloth W and the looper 3 as shown in Fig. 8. The cut-off thread end 10f is not raveled at the sewn end of the cloth W unless it is pulled out from the needle thread loop 8L2 at the end of sewing. In this embodiment, cutting-off of the threads 8LL, 9LL, 10 by the hook 29 and thread cutter 30 is done prior to cut-off of the looper thread loop 10L by the looper thread engaging means 11 and looper thread cutter 12, but the looper thread loop 10L may be cut off simultaneously or before cutting-off of the threads 8LL, 9LL, 10L. In particular, cutting-off of the looper thread loop 10L by the looper thread engaging means 11 and looper thread cutter 12 may be done in a state of lifting the looper thread loop 10L engaged with the looper thread engaging means 11 to the cloth by the needle thread loops 8L2, 9L2, for example, in a state shown in Fig. 6 or Fig. 10. Incidentally, driving of the sewing machine by one stitch or controlling of the start of each cutting device are not specifically described herein, but it may be executed easily by using the rotation control device of a well-known sewing machine motor or controlling means by a rotation signal of a detector provided in the main shaft of the sewing machine. In the embodiment, the pi-shaped working piece 23 is used, but not limited to this, for example, an L-shaped working piece 23' may be formed, and it may be fixed at an adjustable position on the piston rod 21a of the pneumatic cylinder 21 as shown in Fig. 12. In particular, the L-shaped working piece 23' is effective in the sewing machine having narrow bed. Also in the embodiment, the stopper piece 27 is positioned nearly at the side of the working piece 23, but not limited to this, for example, it may be disposed either above or beneath the working piece 23'. Further in the embodiment, the crook lever 16 at the tip end of the looper thread engaging member 14 has a taper portion 16c and two crooks 16a, 16b protruding at the nearly middle position and at the tip end position of the taper portion 16c, but it is not limited to this constitution. For example, as shown in Fig. 13, the tip end side of the looper thread engaging member 14 may be composed of a taper portion 16cc and one crook 16aa consecutive to the tip end side of the taper portion 16cc. Or, as shown in Fig. 14, the tip end side of the looper thread engaging member 14 may be composed of a thread engaging portion 16c3 forming a broad portion 16c1 and a narrow portion 16c2 in steps, and a crook 16aa consecutive to the narrow potion 16c2, and the looper thread engagement with the broad portion or narrow portion may be varied depending on the definition of the moving distance of the driving member by the stopper piece.

Claims: An apparatus for preventing a stitching from raveling, said apparatus comprising; a sewing machine having at least one needle (5, 6) moving vertically, and a looper (3) for forming a double chain stitch (S) formed of needle threads and looper thread (10) in a cloth (W) by collaboration with the needle while the looper oscillates almost horizontally between the forward position and backward position across the needle (5,6), looper thread engaging means (11) for engaging with the looper thread consecutive to the looper from the cloth by moving when the looper is at the forward position and for forming a looper thread loop (10L) consecutive from the cloth (W) at the engaged portion by driving the sewing machine in said engaged state, when the looper is at the forward position, a looper thread cutter (12) for cutting the looper thread loop (10L formed at the engaged portion, and a thread cutter (30) for cutting the loop-shaped needle threads (8L, 9L) consecutive to the needle (5, 6) via the looper (3) from the cloth (W) and the looper thread (10) consecutive to the looper (3) from the cloth between the cloth (W) and the looper (3), characterized by defining means (27) which define the moving distance of said looper thread engaging means (11) and change the length of the looper thread loop (10L) by definition of the moving distance of the looper thread engaging means (11) and said defining means (27), in order to vary the length of the thread end left over in the cloth (W) by said looper thread cutter (12). The apparatus for preventing a stitching from raveling as claimed in claim 1, characterized in that said looper thread engaging means (11) includes at least a looper thread engaging member (14) and a driving member (15) for moving said looper thread engaging member to a engagement position for the looper thread, and said that defining means consists of a stopper piece (27) for defining the moving distance of said driving member. The apparatus for preventing a stitching from raveling as claimed in claim 2, characterized in that said looper thread engaging member (14) has a taper portion (16c) and two crooks (16a, 16b) protruding nearly at the middle position and tip end position of said taper, and that the looper thread engagement with said taper portion across the crook of said middle position can be changed depending on the definition of the moving distance of the driving member (15) by the stopper piece (27). The apparatus for preventing a stitching from raveling as claimed in claim 2, characterized in that said looper thread engaging member (14) has a taper portion and a crook consecutive to the narrow end side of said taper portion. The apparatus for preventing a stitching from raveling as claimed in claim 2, characterized in that said looper thread engaging member (14) has a thread engaging portion having a wide portion and a narrow portion formed in step, and a crook consecutive to the narrow portion of said thread engaging portion, and that the looper thread engagement with the wide portion or narrow portion is varied depending on the definition of moving distance of the driving member (15) by said stopper piece (27). The apparatus for preventing a stitching from raveling as claimed in any one of claims 2 to 5, characterized in that said stopper piece is composed of a rectangular block (27) fixed in the sewing machine at an adjustable angle, and that the moving distance of the driving member (15) is defined by varying the fixing angle of the rectangular block on the sewing machine.

Inventors: NAKANO KAZUYUKI, TOUME FUMIO, WATANABE MASASHI, NAKANO, KAZUYUKI, TOUME, FUMIO, WATANABE, MASASHI, Nakano, Kazuyuki, c/o Pegasus Sewing Machine, Toume, Fumio, c/o Pegasus Sewing Machine, Watanabe, Masashi, c/o Pegasus Sewing Machine
Applicants: PEGASUS SEWING MACHINE MFG CO, PEGASUS SEWING MACHINE MFG. CO., LTD.
Application year: 2000
Main classification: D05B1
IPC codes: D05B65, D05B61, D05B57, D05B1