Method and apparatus for cutting cover thread of multi-needle sewing machine

Abstract: In a cover thread cutter (16) of a multi-needle sewing machine, the hook (32) for thread cutter retreats above the curved cover thread laying finger (12), and captures the cover thread above the curved cover thread laying finger. When pulling up to the cutting position after capturing, it is applied on a specified needle in a manner similar to that of ordinary seam forming, and the thread end is held in this state after being cut off.

Description: The present invention relates to a method and its apparatus for cutting a cover thread of a multi-needle sewing machine using cover thread. Description of the Prior Art A device for automatically cutting the cover thread consecutive to the needle thread seam at the end of sewing after the sewing work, is known. Among the known devices, as disclosed in the Japanese Laid-open Patent Sho. 57-128195, Utility Model Sho. 58-177086, Patent Sho. 59-55286, and Utility Model Sho. 60-179282, at the end of sewing when the needle and feed dog reach the top dead center and the curved cover thread layer finger reaches the left dead center to stop, the cover thread from the right needle thread seam at the end of sewing to the hook of the curved cover thread laying finger is captured and cut by the hook for thread cutter which reciprocates to start from the left oblique rear side of the left needle or the right oblique operator side of the left needle. The cut end of the cover thread at the cut-off thread supply source side is directly clamped in the thread cutter, and is caught by a specified needle or captured by the curved cover thread laying finger when starting next sewing work, so as to be securely sewn into the first needle thread seam. As disclosed in the Japanese Laid-open Patent Sho. 61-45796, at the end of sewing when the needle and feed dog are stopped at the bottom dead center and the finger at the right dead center, the cover thread extending from the right needle thread seam at the end of sewing into the cover thread guide above the finger is captured and cut by the hook for thread cutter which reciprocates from the right oblique rear side of the right needle. The cut end of the cover thread is directly clamped in the thread cutter, so as to be captured by the finger when starting next sewing work. In all these conventional machines, however, since the cover thread is designed to be captured as the hook for thread cutter advances into the space between the top surface of the presser foot and the curved cover thread laying finger, the spacing between the top surface of the presser foot and the curved cover thread laying finger becomes narrow in the case of a thick fabric, so that the hook for thread cutter may not get in easily. These conventional thread cutters are composed of a fixed cutter, a hook for thread cutter which moves in and out as sliding on the fixed cutter, and a leaf spring for pressing the hook to the fixed cutter, in which the cover thread captured by the hook is pulled to the fixed cutter and is cut off by the cutter, and the cut end of the cover thread at the cut-off thread supply source side is pinched and held by and between the hook and the leaf spring. In such devices, however, although it is advantageous that the hook is tightly pressed to the fixed cutter by intensifying the spring pressure of the leaf spring to cut the thread securely, the holding force to the cut thread end increases, and the thread end may not easily slip off from the hook and leaf spring when starting next sewing, which may lead to uneven pulling of the cloth or breakage of the needle. Though it is not a thread cutter for cover thread, a device having a leaf spring for holding the thread end by lightly and elastically contacting with the hook for thread cutter, and a leaf spring for pressing the hook to the fixed cutter, is known. An example of this type is shown in the Japanese Utility Model Publication Sho. 63-10149. According to this device, the thread may be cut off securely by properly adjusting the spring pressures of individual springs, and the cut thread end may be lightly held with a minimum required pressing pressure. However, since the leaf spring is of cantilever type and its free end is pressed to the hook for thread cutter, the leaf spring must be long enough for lightly and elastically contacting with the hook for thread cutter in the case of leaf spring for holding the thread end, and the design is not compact. In this type, the contact area with the hook is small and the holding force is lowered, so that the thread end holding is unstable, and it is always needed to adjust the spring force. Another prior device is shown in US Patent No. 3,848,555. In this device a thread engaging member includes a hook, and is attached to the presser foot carrier. It passes through a slot in the presser foot so as to engage and withdraw a loop of needle and bobbin threads for cutting at a pressing block member on the presser foot carrier. The present invention is dealing with a different problem in that it sets out to cut the cover thread of a multi-needle machine rather than the entwined needle and bobbin threads. It then has to capture the cover thread so that it is available for sewing with the needles in the next phase of sewing. The prior US device is not capable of achieving this objective. SUMMARY OF THE INVENTION The invention is hence intended to capture the cover thread above the curved cover thread laying finger so that the cover thread may be easily and securely captured even in the case of a thick fabric. In this case, when starting next sewing work, it must be arranged to hold the thread end so that the curved cover thread laying finger may securely capture the cover thread. Accordingly the invention provides a method of cutting a cover thread of a multi-needle sewing machine, said sewing machine comprising a left side needle (N1), a right side needle (N2), a curved cover thread laying finger, a thread cutter with a hook, a fixed cutter and a cover thread guide provided above the curved cover thread laying finger, said method being characterised by the steps of: providing said hook at a cutting position above and behind the curved cover thread laying finger, said hook being extendible from and retractable to said cutting position along a line at an oblique angle to a plane containing said curved cover thread laying finger; capturing the cover thread with the curved cover thread laying finger at a first position and laterally moving the curved cover thread laying finger with the captured cover thread to a left end point, said captured cover thread extending between said curved cover thread laying finger and said cover thread guide; stopping the needles (N1, N2) at a top end point and said curved cover thread laying finger near the left end point; extending said hook from said cutting position downwardly towards the cover thread laying finger and below an uppermost surface of said curved cover thread laying finger until said captured cover thread above the curved cover thread laying finger is ensnared by said hook; retracting said hook and said cover thread ensnared by said hook upward along said oblique angle to said cutting position, said cover thread being pulled behind the right side needle (N2) and in front of the left side needle (N1); cutting said cover thread at said cutting position with said fixed cutter in cooperation with said hook; and holding one end of the cut cover thread at said cutting position. In carrying out this method, at the end of sewing, the hook for thread cutter is designed to be extendible from and retractable to the cutting position obliquely behind the left side of the left needle to capture the cover thread above the curved cover thread laying finger and pull up the captured cover thread to the cutting position, so as to cut off and hold the thread end. According to the invention, since the hook for thread cutter advances toward a position above the curved cover thread laying finger, the cover thread can be captured, regardless of the thickness of the fabric. The captured cover thread passes through between specified needles, when the hook for thread cutter retreats behind obliquely to the left side, and is applied on the left side needle necessary for forming the next first seam and is held in this state even after being cut off. Therefore when starting next sewing work, same as at the time of usual seam forming, the cover thread is captured by the curved cover thread laying finger and is sewn into the first needle thread seam, so that skip stitch does not occur. In this method, same as in ordinary seam forming, the cover thread is maintained in a state of extending from the left side of the right side needle up to the cover thread guide through the rear side of right side needle. Therefore when starting next sewing work, it is securely sewn into the first needle thread seam. It is another object of the invention to provide a cover thread cutter assembly for carrying out this method. Accordingly, the invention provides a cover thread cutter assembly for a multi-needle sewing machine comprising a left side needle (N1) and a right side needle (N2), said needles (N1, N2) being mounted for reciprocating vertical movement between top end points and bottom end points; a cover thread guide and a curved cover thread laying finger provided below the cover thread guide, said curved cover thread laying finger being mounted for reciprocating lateral movement between a first position for capturing a cover thread and a left end point where the captured cover thread extends between said curved cover thread laying finger and said cover thread guide. The cover thread cutter assembly comprises a fixed cutter, said fixed cutter being arranged for provision at a cutting position above and behind said curved cover thread laying finger; a thread cutter with a hook, said hook being arranged to be mounted for sliding reciprocating movement along said fixed cutter between said cutting position and a position where the cover thread is securely captured, and a first spring device biasses the hook towards the fixed cutter for cutting the thread; said cover thread cutter assembly being characterised in that the hook is arranged for movement along a path extending from said cutting position downwardly towards the curved cover thread laying finger and below an uppermost surface of said curved cover thread laying finger until said captured cover thread above the curved cover thread laying finger is ensnared by said hook and for retraction upward along a line at an angle which is oblique to a plane containing said curved cover thread laying finger. To achieve the above object, the invention preferably comprises a thread cutter having a spring device comprising a coil spring and a spring retainer, wherein the cut end of the cover thread is held by the spring device with a weaker spring force than the spring for pressing the hook for thread cutter to the fixed cutter. Other objects and features of the invention will be better understood and appreciated from the following detailed description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a flat sewing machine with a cover thread cutter, Fig. 2 is a perspective view when the hook for thread cutter is advanced above the curved cover thread laying finger at the time of cutting the cover thread, Fig. 3 is a perspective view showing the state of capturing of the cover thread by the hook for thread cutter, Fig. 4 is a perspective view showing the cut-off state of the cover thread, and Fig. 5 is a partial sectional side view of essential parts of the thread cutter. DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 shows a flat sewing machine with a needle home position stopping device, in which a curved cover thread laying finger 12 reciprocating laterally before the needle captures and pulls the cover thread in the going stroke, and releases the cover thread in the returning stroke after reaching the left dead center, and a cover thread cutter 16 is installed at the lower left side of the head 14a of the sewing machine 14. The cover thread cutter 16 comprises a bracket 20 mounted on a support shaft 18 projecting sideways from the head 14a, a cutter support frame 24 attached with screws 22 to the bracket 20 so as to be directed to a left needle N1 obliquely nose-diving from the left side of the left needle N1, a fixed cutter 28 fixed with screw 26 to the front end of the cutter support frame 24, with the blade tip adjusted vertically by an adjusting screw 27, as shown in Fig. 5, a hook for thread cutter 32 which is supported by an air cylinder 30 mounted on the cutter support frame 24 and moves back and forth as sliding on the fixed cutter 28 obliquely nose-diving from behind the left side of the left needle N1 to before the needles N1, N2 by the operation of the air cylinder 30, a holder 36 for pinching the hook for thread cutter 32 together with the frame 24, being attached to the cutter support frame 24 with setscrews 34, a first spring device 38 mounted on the holder 36 for tightly pressing the hook for thread cutter 32 to the fixed cutter 28, and a second spring device 40 mounted on the holder 36 for lightly and elastically contact with the hook 32 so as to lightly hold the cut end of the cover thread with a minimum required pressing pressure the second spring device being positioned at the front end side of the hook for thread cutter 32 than the first spring device 38, wherein the first and second spring devices 38 and 40 are composed of spring retainers 46 and 48 of which sections to be engaged with recesses 42 and 44 arranged in the holder 36 are in circular or square cap form and surface contacting with the hook for thread cutter 32 is a flat plane so as to enhance the holding force, and coil springs 50 and 52 which are set in the recesses 42 and 44 and are pressed by the spring retainers 46 and 48. The coil spring 50 of the first spring device 38 has a strong spring force, while the coil spring 52 of the second spring device 40 is designed to have a weak spring force. The first spring device 38 is larger in size than the second spring device 40 so as to be apparently distinguished from the second spring device 40 when assembling. For easier distinguishing, different colors, numbers or codes may be used. The hook for thread cutter 32 which is drawn back by the operation of the air cylinder 30 reaches above the curved cover thread laying finger 12 when moved forward, and when the hook retreats, the hook for thread cutter 32 is designed to capture the cover thread 56 extending from the hook 13 of the curved cover thread laying finger 12 to the cover thread guide 54, at the left side of the left needle N1 near the hook 13. A notch hole 58 is formed in the finger 12 so as to prevent collision with the hook for thread cutter 32 against the finger 12 when the hook for thread cutter 32 moved forward. In the drawing, numeral 60 is a cover thread movable guide attached to a needle holder 62. Numeral 64 is a needle thread, and 66 is a presser foot. In this device composed as described herein, cutting of the cover thread and holding of the thread end are operated as follows. When sewing is over and the pedal (not shown) is released by the operator, the needles N1, N2 are stopped at the top dead center, and the curved cover thread laying finger 12 captures and pulls the cover thread 56 and reaches near the left dead center and stops. In sequence, by the operation of the air cylinder, the hook for thread cutter 32 is projected forward head down obliquely from behind the left side of the left needle N1. When the front end of hook for thread cutter 32 reaches above the curved cover thread laying finger and then draws back rearward, the hook for thread cutter 32 captures the cover thread 56 between the hook 13 and the cover thread guide 54 (Fig. 2), and pulls back obliquely to the left side (Fig. 3). At this time, the cover thread 56 is placed between the left needle N1 and the right needle N2, and is caught in the left needle N1 and is bent backward obliquely to the left. When the hook for thread cutter 32 pulls the cover thread 56 and retracts from the fixed cutter 28, the thread 56 is cut off, and the cut thread end of the thread supply source is pinched between the second spring device 40 and the hook for thread cutter 32. In this state, the cover thread 56 is pulled out of the cover thread guide 54, and is hooked on the right needle N2 from the rear side and is hooked on the left needle N1 from the front side to be held, so that the cover thread is sewn into the first needle thread seam when starting the next sewing work.

Claims: A method of cutting a cover thread of a multi-needle sewing machine, said sewing machine comprising a left side needle (N1), a right side needle (N2), a curved cover thread laying finger (12), a thread cutter (32) with a hook, a fixed cutter (28) and a cover thread guide (54) provided above the curved cover thread laying finger (12), said method being characterised by the steps of: providing said hook at a cutting position above and behind the curved cover thread laying finger (12), said hook being extendible from and retractable to said cutting position along a line at an oblique angle to a plane containing said curved cover thread laying finger (12); capturing a cover thread (56) with the curved cover thread laying finger (12) at a first position and laterally moving the curved cover thread laying finger (12) with the captured cover thread (56) to a left end point, said captured cover thread (56) extending between said curved cover thread laying finger (12) and said cover thread guide (54); stopping the needles (N1, N2) at a top end point and said curved cover thread laying finger (12) near the left end point; extending said hook from said cutting position downwardly towards the cover thread laying finger (12) and below an uppermost surface of said curved cover thread laying finger (12) until said captured cover thread (56) above the curved cover thread laying finger (12) is ensnared by said hook; retracting said hook and said cover thread (56) ensnared by said hook upward along said oblique angle to said cutting position, said cover thread (56) being pulled behind the right side needle (N2) and in front of the left side needle (N1); cutting said cover thread (56) at said cutting position with said fixed cutter (28) in cooperation with said hook; and holding one end of the cut cover thread (56) at said cutting position. A cover thread cutter assembly for a multi-needle sewing machine comprising a left side needle (N1) and a right side needle (N2), said needles (N1, N2) being mounted for reciprocating vertical movement between top end points and bottom end points; a cover thread guide (54) and a curved cover thread laying finger (12) provided below the cover thread guide (54), said curved cover thread laying finger (12) being mounted for reciprocating lateral movement between a first position for capturing a cover thread (56) and a left end point where the captured cover thread (56) extends between said curved cover thread laying finger (12) and said cover thread guide (54), said cover thread cutter assembly comprising a fixed cutter (28), said fixed cutter being arranged for provision at a cutting position above and behind said curved cover thread laying finger (12); a thread cutter (32) with a hook, said hook being arranged to be mounted for sliding reciprocating movement along said fixed cutter (28) between said cutting position and a position where the cover thread is securely captured and a first spring device (38) biasses the hook towards the fixed cutter (28) for cutting the thread; said cover thread cutter assembly being characterised in that the hook is arranged for movement along a path extending from said cutting position downwardly towards the curved cover thread laying finger (12) and below an uppermost surface of said curved cover thread laying finger (12) until said captured cover thread (56) above the curved cover thread laying finger (12) is ensnared by said hook and for retraction upward along a line at an angle which is oblique to a plane containing said curved cover thread laying finger (12). A cover thread cutter assembly for a multi-needle sewing machine according to claim 2, characterised in that the curved cover thread laying finger (12) has a notch hole (58) provided for permitting the front end of the hook for the thread cutter to enter in order to avoid collision with the curved cover thread laying finger against the hook for the thread cutter. A cover thread cutter assembly for a multi-needling sewing machine according to claim 2 or claim 3, characterised in that in addition to the first spring device (38) for pressing the hook for the thread cutter to the fixed cutter the cover thread cutter further comprises a second spring device (40) for holding the cut thread end together with the hook for the thread cutter by lightly and elastically contacting the hook for thread cutter, and both spring devices are composed of coil springs and spring retainers, and the second spring device is weaker in spring force of the coil spring than the first spring device, and is disposed at the front end side of the hook for the thread cutter. A cover thread cutter assembly for a multi-needle sewing machine according to claim 4, characterised in that each spring retainer (46, 48) is shaped like a cap, and its contact surface with the hook for thread cutter is a flat plane. A cover thread cutter assembly for a multi-needle sewing machine according to claim 4, characterised in that the first spring device (38) and the second spring device (40) are different in size.

Inventors: ICHIMURA TAKASHI, KAGEYAMA YOSHIKAZU, OKADA KOICHI, ICHIMURA, TAKASHI, KAGEYAMA, YOSHIKAZU, OKADA, KOICHI, ICHIMURA, TAKASHI, C/O PEGASUS SEWING MACH. MFG., KAGEYAMA, YOSHIKAZU, C/O PEGASUS SEWING MACH. MFG., OKADA, KOICHI, C/O PEGASUS SEWING MACHINE MFG. CO.
Applicants: PEGASUS SEWING MACHINE MFG CO, PEGASUS SEWING MACHINE MFG. CO., LTD.
Application year: 1990
Main classification: D05B65
IPC codes: D05B57, D05B65