EP1689925B1 - Method and device for fixing a thread to a workpiece - Google Patents

Abstract

A warp sewing machine attaches a thread to a tea bag or a medical dressing in a process in which the thread anchorage stitch is first created on the work piece and the needle (2) brought to a stop with a loop around a form (1). A pick-up hook then draws a further length of thread from the bobbin and the thread is separated by a cutter. The thread with loop are then surrendered from the sewing machine. Also claimed is a suitable warp sewing machine.

Description

The invention relates to a method and a device for fastening a connecting or holding thread to a workpiece, for example a tea bag or a wound pad or to a medical pad by means of a sewing machine, preferably a chain stitch sewing machine for producing stitch-type thread chain stitches 101 ,

By the DE G 94 11 639.3 U1 a bag made of paper or the like is known, which is closed by means of a thread by at least one seam, wherein the seam-forming thread extends beyond the actual seam and its end is sewn with a label. Since the length of the thread located between the bag and the label is generally between 10 and 20 cm, this thread length must be removed after the closure of the tea bag and the thread end attached to the label.
A solution for this is not disclosed in the prior publication.

When setting up US 2 307 998 the tea bag is first verschlos-sen by means of a number of stitches formed fastening seam, after which the connecting thread to the label to a certain length "disengaged", ie the connecting thread is formed by an at least two-seam without sewing material, as shown in Figure 17 of the prior publication is shown. In the area of the label, this connecting seam formed as a "warp seam" again merges into a fastening seam whose free end projects beyond the edge of the label and there again is a warp seam.
Since this is an at least two-strand chainstitch, the thread consumption is relatively large and accordingly expensive. In addition, the Kettelnaht thus formed is substantially thicker than the strength of the monofilament, whereby the above-described solution for use in the medical field, in which usually only very small thread sizes desirable or approved, poorly suited.

US-A-5 887 533 discloses an apparatus wherein the thread leg leading to the thread supply through the interaction of the stationary on a needle plate knife arranged with a movable knife below the material sewn through. The invention is therefore an object of the invention to provide a more favorable in terms of thread consumption solution, which at the same time has a relation to a Kettelnaht smaller thickness, but nevertheless ensures sufficient security of the fastening seam.

A first step of the solution according to the invention is the use of a single-thread chain stitch (stitch type 101), which can be formed with both a rotating and a swinging gripper. However, this type of stitch, in which the thread-guiding needle punctures each in the still hanging on the gripper and by this spread thread loop of the previous puncture, however, has the disadvantage that the seam thus formed from the side of the last stitch formed relative easy to raise.

A second step of the solution according to the invention is therefore in the measure to make the stitch formation of the respective last stitch of a fastening seam so, and to position the connecting or holding thread with respect to the last stitch, that this through the connecting or holding thread against pulling is secured.

This is achieved according to the invention by a process comprising steps a) to e).

By the measures to shut down the needle still hanging on the gripper thread loop and to detect when the thread tensioning device from the gripper to the needle leading run of the thread loop between the needle and workpiece and the thread supply through the needle thread to form one of the length of the connecting or holding thread retighten correspondingly long thread loop, it is possible to achieve a correspondingly long connecting or holding thread, wherein the leg length to be pulled out of the thread loop substantially corresponds to only half the length of the connecting or holding thread.
Since both the extended length of the thread loop and the length of the leading over the gripper to the workpiece thread loop form the total length of the connecting or holding thread and when passing the workpiece from the stitch pattern inevitably the entire length of the loop of thread formed by the last recess of the needle formed in the workpiece puncture hole and the last formed on the workpiece thread loop to the bottom of the workpiece, forms the Overall length of the connecting or holding thread as far as a security against picking up the seam formed, as for pulling the seam, the entire length of connecting or holding thread would have to be pulled through the last formed thread loop to the top of the workpiece.
While in known thread cutting devices for single-thread chain stitch sewing machines hanging over the gripper thread loop is usually cut such that the workpiece remaining end of the thread is as short as possible, in the teaching of the invention, the separation process is carried out in such a way that the remaining on the workpiece free end of the thread is as long as possible and due to its implementation provides both by the workpiece in the last puncture of the needle as well as by the last formed on the workpiece thread loop security of the seam formed against drawing.

The extraction of the thread loop can advantageously take place by means of a thread puller having a barb, which is displaceable along a movement path essentially parallel to the main shaft of the sewing machine, the length of its withdrawal movement being adjustable as a function of the desired length of the connecting or holding thread.

In order to be able to cut off the correct leg of the thread loop lengthwise, a separation device for the thread loop is arranged in the region of the needle, whose distance from the needle can be adjustable to change the free length of the end of the needle thread.

In order to be able to perform the separation of the same length after pulling out the thread loop, it is advantageous, leading from the thread tensioning device to the thread loop thread in the region of the needle eye before separating the thread loop by means of a clamping device to pinch. For this purpose, in the area of the needle, a clamping device is also provided for the thread leading from the thread tensioning device to the thread loop.
It is expedient if the separating device and the clamping device are arranged on one side of the needle, preferably on the side facing the thread loop side of the needle.

In order to sew the resulting during the cutting of the thread loop free end of the needle thread during the formation of the fastening seam, it is expedient if the clamping device is movable from one side of the needle to the other side of the needle and during the formation of the fastening seam as thread rug for the initial thread of Attachment seam is used. The clamping device can be moved by its the thread during the separation process fixing the first working position in a second working position in which it brings the free end of the thread in parallel to form the stitches of the fastening seam position and in this similar to the zig-zag movement of Needle bar of a zigzag sewing machine performs lateral movements in the rhythm of the needle bar movement, so that the starting thread of the free needle thread alternately on one side and then on the other side is pierced and sewn.

Since, in the method according to the invention for forming the connecting or holding thread, a relatively large thread length is drawn through the needle eye and the needle is therefore subjected to bending, it is advantageous to provide a supporting device for the needle in the region of the needle, which during removal of the thread loop on the shaft the needle rests.

Advantageous further embodiments of the invention are specified in claims 10 and 11.

Further details and advantages of the invention will become apparent from the following description of the method and an embodiment of an apparatus for carrying out the method shown in the accompanying drawings.

It shows:

Fig. 1:

the course of the threads of the chain stitch seam in the top dead center of the needle stopped gripper with the initial thread 25 and the attachment seam 26;

Fig. 2:

the course of the threads during the extraction of the thread loop with the essential parts of the device used to carry out the method;

3:

an enlarged view of the detail A of Fig.2

4:

a plan view of the workpiece with the stitched through the attachment seam starting thread and the connecting or holding thread;

Fig. 5:

a view of the underside of the workpiece with the thread loops of the fastening seam 26 and the connecting or holding thread 10;

To carry out the method according to the invention is a chain stitch sewing machine for the production of single-thread chain stitches the stitch type 101. Sewing machines of this type have a arranged below the needle plate gripper 1, which is driven either rotating or swinging. In the illustrated embodiment of the invention is based on a rotating gripper, which cooperates with a thread-guiding needle 2, which is driven up and down.
To drive the needle 2 and gripper 1 is a not shown position motor in different angular positions of the arm shaft and thus in different positions of the needle receiving needle bar 3 is stopped. In the present case, the arm shaft can be stopped, inter alia, in an angular position corresponding to the top dead center position of the needle bar 3, in which the thread loop 4 still hangs over the gripper 1. Therefore, the thread runs from a thread supply to a releasable thread tensioning device and from there via the eye 5 of the needle 2 to this leading strand 6 of the thread loop 4. The other strand 7 of the thread loop 4 leads to the bottom of the workpiece W and from there through the last formed Thread loop 15 through the insertion hole 8 in the workpiece W through to the top of the workpiece W.

For detecting and removing the run 6 of the thread loop 4 is provided with a barb 9 thread-pulling device 11 is provided, which is mounted in the housing, not shown, of the sewing machine and by means of a drive, not shown, within a plane parallel to the Nähgutauflagefläche plane is displaceable. With the help of the thread puller 11, the strand 6 can be pulled out to a thread loop 12, wherein the length of the connecting or holding thread 10 can be determined by the size of the Ausziehhubes the thread puller 11 and by changing the size of the Ausziehhubes the length of the connecting or holding thread 10th is changeable. Regardless of the size of the pull-out stroke of the thread-pulling device 11, one leg 13 of the drawn-out loop 12 leads to the eye 5 of the needle 2 and the other leg 14 passes through the insertion hole 8 in the workpiece W and through the last-formed thread loop 15 resting on the underside thereof to the strand 6 hanging on the gripper 1 thread loop 4th

In the region of the needle 2, a separating device 16 and a clamping device 17 are arranged above the workpiece W, which can be accommodated by a respective carrier not shown and attached to the housing of the sewing machine and slidably mounted on these parallel to the extension direction of the thread puller 11. The separating device 16 may be formed by a mechanically or pneumatically actuated scissors. By changing the distance between the needle 2 and the separator 16, the length of the free end of the respective starting thread 25 for each next fastening seam 26 is adjustable.

The side of the separator 16 arranged clamping device 17 is essentially formed by two jaws 18,19, wherein the jaws 18 may be fixed and connected to its carrier, while the jaws 19 pivotally mounted on the jaws 18 and held by a spring in its open position can be.
To close the clamping device 17 may also serve a mechanical or pneumatic drive, both drives so To agree with each other, that when they first actuate the clamping device 17 is closed and only then the separator 16 is activated.

The spatial assignment of the thread-pulling device 11 to the separator 16 and clamping device 17 is such that the thread-puller 11 can move through the separating and clamping device 16,17 open therethrough, but only the leg 13 of the thread loop 12 to be pulled out into the effective range of Separator 16 and the clamping device 17 passes.

In a preferred embodiment of the device according to the invention, the clamping device 17 may additionally be pivotable about an axis perpendicular to the Nähgutauflagefläche the sewing machine axis to bring the separated from the thread loop 12 length of the starting thread 25 of the subsequent sewing seam 26 in their sewing direction and through them about sewing.
In order to shift the puncture of the needle 2 alternately from one to the other side of the starting thread 25, the clamping device 17 can be given by a further drive the transverse movements of the needle bar of a zigzag sewing machine corresponding periodic transverse movements, so that the needle 2 during the formation of the fastening seam 26 alternately punctures on one and the other side of the fastening seam 26, in order thereby to fix the relative position of the starting thread 25 of the fastening seam 26.

A further preferred embodiment of the invention provides for the change of the insertion position of the needle 2, instead of a so-called straight-stitch-single-chain stitch sewing machine to use a known per se Zick-Zack single-chain stitch sewing machine. In this case, it is sufficient if the initial thread 25 of the fastening seam to be subsequently formed 26 is brought by means of the clamping device 17 in a stitch pattern direction of the attachment seam 26 parallel position, in which case the changing insertion position of the needle 2 by the usual in zigzag sewing machines transverse movements the needle 2 is reached. Such an embodiment of the invention has the advantage that the periodic transverse movements the clamping device 17, and thus the drive for generating these transverse movements is omitted and is replaced by the usual in zig-zag sewing machines transverse movements of the needle 2. This offers at the same time the opportunity to use existing in conventional zig-zag sewing adjustment for the so-called Überstichbreite and either sew only the initial thread 25 with zigzag stitches and the remaining length of the attachment seam 26 to form with straight stitches, or sew the entire fastening seam 26 with zig-zag stitches.

Since the extraction of the thread loop 12 through the thread puller 11 due to possibly many deflections in the thread path a considerable frictional resistance can prevent, which can lead to bending of the needle 2, a support means 21 is provided for the shaft of the needle 2. This can be formed by a rigid arm 22 attached to the machine housing, which bears against the shaft of the stationary needle 2 during the pull-out movement of the thread-pulling device 11. In a preferred and illustrated in the drawing embodiment of the support means 21, the arm 22 may have a passage opening 23 for the needle 2, so that the shaft of the needle 2 is capable of supporting on the inner wall of the passage opening 23.

For carrying out the method according to the invention, it is assumed that the starting thread 25 is brought by the clamping device 17 in the correct relative position to the workpiece for the fastening seam 26 to be formed. During the sewing of the initial thread 25 of the fastening seam 26, the clamping device 17 performs periodic transverse movements, so that the needle 2 mutually punctures the starting thread 25. After sewing over the starting thread 25, the formation of the fastening seam 26 is continued into the region of the edge zone of the workpiece W.

Subsequently, the sewing machine with its needle located in its upper dead center position 2 is shut down with simultaneous opening of the (not shown) thread tensioning device. In In this position, the thread loop 4 still hangs over the gripper 1, wherein the strand 6 of the thread loop 4 leads through the last formed thread loop 15 and the insertion hole 8 in the workpiece W to the needle 2 and from here via the thread tensioning device to the thread supply. The other strand 7 of the thread loop 4 also passes through the last formed thread loop 15 and the insertion hole 8 in the workpiece W through the last stitch of the fastening seam 26, as in Fig. 1 is shown.

In this position, the thread loop 4 whose strand 6 is detected above the workpiece W from the barb 9 of the thread puller 11 and based on Fig. 2 pulled out to the right to a thread loop 12. The leg 13 of the thread loop 12 passes through the separator 16 and the clamping device 17 to the needle 2 and through the eye 5 therethrough to the thread tensioning device and the thread supply. In this case, the leg 13 is guided through the open separating device 16 and between the clamping jaws 18, 19 of the likewise open clamping device 17.

Now the clamping device 17 is closed and the leg 13 of the thread loop 12 separated by the separator 16. The leading of the separator 16 to the needle 2 and held in the clamping device 17 portion of the leg 13 forms the initial thread 25 for the formation of the next fastening seam and is brought by the clamping device 17 in a stitch direction parallel to their position in the next sewing cycle in the to be sewed during the formation of the next attachment seam as described above. During the removal of the workpiece W, the remaining length of the leg 13 and the associated legs 14 are guided through the insertion hole 8 in the workpiece and the latter formed last thread loop 15 to the underside of the workpiece W and form together with the strand 6 of the needle bar 3 and the through the last formed yarn loop 15 leading run 7 of the thread loop 4 the connecting or holding thread 10, which has a predeterminable length of according to the size of the Ausziehhubes. Since this entire thread length for pulling the chain stitch from the bottom of the workpiece W would have to be performed by 15 last formed at this thread loop 15, the connecting or holding thread forms due to its relatively large length high security against mounting the thread chainstitch seam.

Claims (9)

1. A method for fastening a connecting or retaining thread to a workpiece with the aid of a sewing machine forming a single-thread chain stitch seam (stitch type 101), comprising the following steps:

   a) forming a predetermined number of stitches for producing a fastening seam (26), preferably in the edge zone of the workpiece;

   b) bringing the needle (2) to rest with thread loop (4) still suspended on the gripper (1) and opening the thread tensioning device:

   c) grasping the strand (6) of the thread loop (4) leading from the gripper (1) to the needle (2) with the needle brought to a standstill above the workpiece, between said workpiece and the needle (2) and drawing thread from the thread supply through the needle (2) to form a long thread loop (12) corresponding to the length of the connecting or retaining thread (10);

   d) cutting through the side (13) of the thread loop (12) leading to the needle (2) above the workpiece in the region of the needle (2) before the needle eye (5);

   e) guiding the workpiece away from the stitch forming location in such a manner that the side (14) of the thread loop (12) leading to the thread loop (4) moves through the last puncture hole (8) in the workpiece and through the last thread loop (15) of the fastening seam (26) formed thereon through to the workpiece underside.
2. The method according to claim 1, characterised in that the thread (side 13) leading from the thread tensioning device to the thread loop (12) is clamped in the area of the needle eye (5) before separating the thread loop (12) by means of a clamping device (17).
3. A device for carrying out the method according to claim 1, comprising

   a.) a single-thread chain-stitch sewing machine having a needle, a gripper and a thread tensioning device for forming a fastening seam containing a predetermined number of stitches;

   b.) a snag (11) having a barb (9) for grasping the strand (8) of the thread loop (4) leading from the gripper (1) to the needle (2) between needle (2) and workpiece and for drawing thread from the thread supply through the needle (2) to form a long thread loop (12) corresponding to the length of the connecting or retaining thread (10) which is displaceable along a movement path directed substantially parallel to the main shaft of the sewing machine;

   c.) a clamping device (17) disposed in the area of the needle (2) for the side (13) of the thread loop leading from the thread tensioning device to the thread loop (12);

   d.) a separating device (16) disposed in the area of the needle (2) for the drawn-out thread loop (12).
4. The device according to claim 3, characterised in that the length of the movement of the snag (11) is adjustable.
5. The device according to claim 3, characterised in that the separating device (16) and the clamping device (17) are disposed on one side of the needle (2), preferably on the side of the needle (2) facing the thread loop (12).
6. The device according to claim 3, characterised in that the clamping device (17) is movable from one side of the needle (2) to the other side of the needle (2) and during the formation of the fastening seam (26) serves as a thread holder for the initial thread (25) of the fastening seam (26).
7. The device according to claim 3, characterised by a supporting device (21) for the needle, which is disposed in the area of the needle (2) and supports the stem of the needle (2) during withdrawal of the thread loop.
8. The device according to claim 3 and 7, characterised in that the supporting device (21) and the snag (11) can be brought successively into operative position.
9. The device according to claim 3, characterised in that the sewing machine is a zigzag sewing machine.

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