EP1847641B1 - Thread drawing knife for a sewing machine - Google Patents

Abstract

The second rotation stop (38) is fastened to the thread-pulling blade (29). A positioning restraint (41) secures the thread-pulling blade in the normal position when the shuttle (19) turns in the opposite direction. In this position the second rotation stop (38) works with the second spool casing stop (40). The second stop is molded-on integrally with the thread-pulling blade. A projection (39) opposite the second stop on the thread-pulling blade, transitions smoothly into the blade body. A deflection mechanism operates with the thread pulling blade drive (49), this causes displacement of the blade from its normal position, into a thread-gripping position, by moving the positioning restraint into a release position. Further mechanical details of the mechanism are provided. The thread pulling blade drive includes an electromagnet.

Description

The invention relates to a thread-pulling knife for a sewing machine, in particular for a lockstitch sewing machine, according to the preamble of claim 1.

Such thread-pulling knives are known from the DE 101 17 560 C1 and the DE 101 23 075 C1 , With regard to a trouble-free yarn course of a needle fed upper thread of the sewing machine there is still room for improvement in demanding applications.

It is therefore an object of the present invention, a thread-pulling knife of the type mentioned in such a way that a trouble-free yarn path, in particular of the needle or upper thread of the sewing machine results.

This object is achieved by a thread-pulling knife with the features specified in the characterizing part of claim 1.

By the extended end portion prevents in particular the needle thread is caught in the loop undesirable on the thread-pulling knife or other sewing machine components. It is also ensured that, in particular, the needle thread does not undesirably wrap around the thread-pulling knife. Overall results in a trouble-free threadline. The rounded end section additionally ensures that the threadline is not disturbed by the thread-pulling knife.

A length of the end portion according to claim 3 has been found to ensure a trouble-free thread course particularly suitable.

An arcuate design of the thread-pulling knife according to claim 4 ensures that a main body of the thread-pulling knife disturbs the threadline as little as possible.

Fig. 1

eine Vorderansicht einer Doppelsteppstichnähmaschine;

Fig. 2

eine Draufsicht auf einen Ausschnitt der Nähmaschine in vergrößertem Maßstab entsprechend dem Sichtpfeil II in Fig. 1;

Fig. 3

eine innere Details freigebende Stirnansicht auf einen Ausschnitt der Nähmaschine entsprechend dem Sichtpfeil III in Fig. 1 in vergrößertem Maßstab;

Fig. 4

eine zu Fig. 2 ähnliche Ansicht mit einem Fadenziehmesser in einer gegenüber einer Grundstellung nach Fig. 2 entgegen dem Uhrzeigersinn verschwenkten Fadenerfassungsstellung;

Fig. 5

eine perspektivische Ansicht von Komponenten der Nähmaschine, insbesondere von einem mit einem Fadenziehmesser-Antrieb zusammenwirkenden Umlenkmechanismus einerseits zur Positionssicherung des Fadenziehmessers in der Grundstellung und andererseits zur Verlagerung des Fadenziehmessers zwischen der Grundstellung und der Fadenerfassungsstellung;

Fig. 6 und 7

kinematische Darstellungen des Umlenkmechanismus nach Fig. 5, wobei Fig. 6 den Umlenkmechanismus in der Grundstellung und Fig. 7 den Umlenkmechanismus in der Fadenerfassungsstellung des Fadenziehmessers zeigt;

Fig. 8

eine perspektivische Darstellung des Fadenziehmessers; und

Fig. 9

einen Schnitt gemäß Linie IX-IX in Fig. 3.

An embodiment of the invention will be explained in more detail with reference to the drawing. In this show:

Fig. 1

a front view of a lockstitch sewing machine;

Fig. 2

a plan view of a section of the sewing machine in an enlarged scale corresponding to the viewing arrow II in Fig. 1 ;

Fig. 3

an inner details releasing front view of a section of the sewing machine according to the viewing arrow III in Fig. 1 on an enlarged scale;

Fig. 4

one too Fig. 2 similar view with a thread-pulling knife in one opposite to a basic position Fig. 2 counterclockwise pivoted thread detection position;

Fig. 5

a perspective view of components of the sewing machine, in particular of a cooperating with a thread-pulling knife drive deflection on the one hand to secure the position of the thread-pulling knife in the normal position and on the other hand for shifting the thread-pulling knife between the basic position and the thread detection position;

6 and 7

kinematic representations of the deflection mechanism according to Fig. 5 , in which Fig. 6 the deflection mechanism in the normal position and Fig. 7 shows the deflection mechanism in the thread detection position of the thread-pulling knife;

Fig. 8

a perspective view of the thread-pulling knife; and

Fig. 9

a section along line IX-IX in Fig. 3 ,

A lockstitch sewing machine 1 has a base plate 2 with a stand 3 extending upward therefrom and an angled arm 4. The latter ends in a head 5. In the arm 4, an arm shaft 6 is rotatably supported. This drives in the head 5 a crank mechanism 7 with a thread lever 8 at. The crank mechanism 7 is drivingly connected to a needle bar 9 mounted axially displaceably in the head 5. This has at its lower end a needle 10. The needle 10 is moved up and down by the crank mechanism 7 on a vertical axis 11. The needle 10 leads in an eye from a spool 12 via a thread tensioning device and the thread lever 8 supplied needle thread 13th

The base plate 2 carries a screw-mounted support plate 14, on which a workpiece 15 rests. The support plate 14 is formed with a recess 16 for the passage of a feed dog 17. The latter has a tap hole 18 for the passage of the needle 10. The feed dog 17 is in a known manner in drive connection with a arranged below the base plate 2 thrust and screw jack.

Below the platen 14 is a gripper 19 having a gripper body 20 with a gripper tip 21. In the gripper body 20, a cup-shaped coil housing 22 is mounted for receiving a looper thread supply.

The gripper 19 is rotatable about a vertical gripper axis 23. A sewing operation direction of rotation 24 runs in Fig. 2 clockwise about the gripper axis 23. The gripper body 20 is fixedly connected to a shaft 25 which is coaxial with the gripper axis 23. The shaft 25 is rotatably mounted in a bearing block 26 screwed to the base plate 2. In this, a drive shaft 27 is mounted, which is connected to a arranged in the interior of the bearing block 26 gear transmission. The gear transmission has a gear ratio of 1: 2, so that in one revolution of the drive shaft 27 located on the shaft 25 gripper body 20 rotates twice. The drive shaft 27 is drivingly connected to the arm shaft 6 via a belt drive 28.

To cut off the looper thread, a thread-pulling knife 29 is used. The thread-pulling knife 29 is located between an in Fig. 2 illustrated basic position and a in Fig. 4 shown thread detection position about a parallel to the gripper axis 23 pivot axis 30 pivotally. The thread-pulling knife 29 has one in the view Fig. 2 reminiscent of a sickle basic form, the free end in the basic position in the view after Fig. 2 extends around the coil housing 22 around. In the thread-detecting position of the thread-pulling knife 29, the stitch hole 18 is adjacent to one Detecting groove 31 of the thread pulling knife 29 with a groove bottom side cutting edge 32. The detection groove 31 is executed in a right angle to a horizontally extending base body 32a angled edge portion 32b of the thread pulling knife 29. An extended free end portion 32 c of the thread-pulling knife 29 is in the plan view of the Fig. 2 and 4 executed rounded end. The length of the free end portion 32c of the thread-pulling knife 29 results in that the needle thread 13 does not undesirably wrap around the thread-pulling knife during looping. The rounded shape of the free end portion 32c leads to a trouble-free yarn path of the needle thread 13 and the looper thread.

Fixed to the base plate 2 on a boom is a stationary counter knife 33, which cooperates to cut the thread when pivoting the thread pulling knife 29 of the Fadenerfassungs- in the basic position.

Integrally formed on the coil housing 22 is a holding finger 34th
In the sewing operation direction of rotation 24, the spool housing 22 is secured against rotation about the gripper axis 23 by a first anti-rotation stop 35. The latter is designed as an end face of a Kragarms 36 which is fixedly bolted to the base plate 2. At the first anti-rotation stop 35 is located to prevent rotation of the bobbin case 22, a first bobbin case counter-stop 37, which is formed by a first anti-rotation stop 35 facing surface of the retaining finger 34.

In the opposite direction to the sewing operation direction of rotation 24, in the view Fig. 2 that is counterclockwise, the coil housing is secured against rotation about the gripper axis 23 by a second anti-rotation stop 38. The latter is formed by a integrally formed on the free end of the thread pulling knife 29 stop surface, which represents the end face of a lower projection 39, the edge opposite to the second anti-rotation stop 38 without edges in the main body 32a of the thread pulling knife 29. The second anti-rotation stop 38 is thus fixed to the thread-pulling knife 29.

In the basic position of the thread-pulling knife 29, the second anti-rotation stop 38 cooperates with a second bobbin case counter-stop 40. This is formed by the first coil housing counter-stop 37 opposite and the second anti-rotation stop 38 facing surface of the retaining finger 34 of the coil housing 22nd

When the gripper 19 rotates in the sewing operation direction of rotation 24, the abutment of the first anti-rotation stopper 35 on the first bobbin case counter stop 37 prevents the bobbin case 22 from rotating with the gripper 19. As soon as the gripper 19 rotates in the opposite direction, which may occur during adjustment work on the sewing machine or even when the sewing needle 10 is moved back to a top thread position after a successful thread trimming operation, a maximum clearance between the sewing needle 10 and the platen 14th to adjust for a work piece 15, the installation of the second anti-rotation stopper 38 on the second bobbin case counter-stop 40 prevents the bobbin case 22 from contacting the gripper 19 in the opposite direction co-rotate. For this purpose, the thread-pulling knife 29 is secured in the basic position in order to receive a force exerted by the retaining finger 34 on the thread-pulling knife 29 via the stops 40, 38.

This securing the thread pulling knife 29 in the basic position makes a position securing device 41, the perspective in the Fig. 5 and their kinematic relationships in the 6 and 7 are shown. The core of the position assurance device 41 is a deflection mechanism 42. The latter has a pivot lever 43 which rotatably via a stationary mounted shaft 44 with the in Fig. 5 not shown thread-pulling knife 29 is connected. The shaft 44 extends coaxially to the pivot axis 30. About a hinge connection 45 with the pivot axis 30 parallel hinge axis 46 of the pivot lever 43 is articulated to a locking lever 47. The safety lever 47 is in shear connection with a lifting ram 48 of a thread-pulling knife drive 49. For this purpose, the securing lever 47 rests on the lifting ram 48 via a cam 47a. The thread-pulling knife drive 49, which is designed as an electromagnet, serves for displacing, on the one hand, the thread-pulling knife 29 from the basic to the thread-detecting position and, on the other hand, for displacing the position-securing device 41 from one to the other Fig. 5 and 6 shown securing position in a in Fig. 7 shown release position in which a pivoting of the thread-pulling knife 29 is possible. The safety lever 47 has a latch 50 designed as the first securing portion which is secured in the securing position of the position securing device 41 against a stationary and engaging in the first securing portion 50 second securing portion, which is designed as fixed and fixed to the base plate 2 bolt 51. Fig. 7 shows the disengaged from the pin 51 pawl 50 in the release position of the position assurance device 41st

The safety lever 47 and the pivot lever 43 are biased in the securing position of the position assurance device 41 by a biasing spring 52. The latter is designed as a leg spring, one leg 53 of the safety lever 47 and the other leg 54 rests against a pin 55 fixed to the pivot lever 43. The biasing spring 52 is looped between the legs 53, 54 about a pin 55 a, which is fixed to the safety lever 47.

In particular Fig. 5 can be seen, is the cantilever 36 with the first anti-rotation stop 35 only slightly above the bobbin case 22 with the holding finger 34 over. This makes it possible to arrange the coil housing 22 such that only a minimal gap remains between the thread-pulling knife 29 and an upper side of the coil housing 22. This allows an arrangement of the cutting edge 32 very close to the stitch hole 18, so that 15 remaining thread ends are short on the underside of the workpiece 15 after the cutting process. In addition, by this arrangement of the bobbin case 22, the yarn path of the looper thread and the needle thread 13 in the loop formation by the gripper 19 is improved.

The lockstitch sewing machine 1 operates as follows: In the normal sewing operation, the thread-pulling knife 29 is in the home position and the position securing device 41 is in the securing position. Thus, the bobbin case 22 is secured via the anti-rotation stops 35, 38 and the bobbin case counter-stops 37, 40 against rotation about the gripper axis 23 in both directions of rotation. With the help of the gripper 19 takes place in a known manner, the looping and knotting of looper thread and needle thread 13 for lockstitch.

To initiate the Fadenabschneidvorgangs the thread-pulling knife drive 49 is actuated, so that the lifting ram 48 extends. The Hubstempel 48 pushes the cam 47a in the representations of 6 and 7 downward. The thrust force of the Hubstempels 48 causes the locking lever 47 to the articulation 45 in the 6 and 7 is pivoted clockwise. This is done against the biasing force of the biasing spring 52, until the lifting ram 48 opposite surface of the locking lever 47 comes into contact with the pivot lever 43. At the same time the pawl 50 moves out of the bolt 51 until the position of the deflection mechanism 42 after Fig. 7 is reached. The disengaged position of the second securing portion 51 represents a thread detection drive position, in which a free pivoting of the thread pulling knife 29 from the basic position is possible.

In this position, the pivot lever 43 is about the shaft 44 with respect to the position Fig. 6 pivoted counterclockwise. As a result, a roller 56 mounted on a roller lever 57 fixedly connected to the pivot lever 43 comes into rolling contact with an axial cam 58. The latter is rotatably connected to the drive shaft 27. By rolling the roller 56 on the axial cam 58 in the release position of the position securing device 41 is now the pivotal movement of the thread pulling knife 29 initially from the basic position Fig. 2 in the thread detection position Fig. 4 enforced. In this thread detecting position, the looper thread and the needle thread 13 enter the engaging groove 31 of the thread pulling knife 29. Subsequently, the rolling contact of the roller 56 on the axial cam 58 forces a return of the thread-pulling knife 29 from the thread-detecting position to the basic position. On this return, the thread is working together cut the cutting edge 32 with the counter knife 33. After this return and complete withdrawal of the Hubstempels 48 forces the biasing spring 52, the cam 47a of the locking lever 47 again away from the pivot lever 43 until the pawl 50 engages again in the pin 51.

During the Fadenabschneidvorgangs a rotation of the coil housing 22 against the Nähbetriebs-direction of rotation is not required. As long as the thread-pulling knife 29 is in the thread detection position, the approach 39 does not hinder the threadline of looper thread and needle thread 13.

Claims (3)

1. Thread withdrawal blade (29) for a sewing machine (1), the sewing machine comprising a shuttle (19) which may be rotated about a vertical shuttle axis (23) in a rotational direction (24) during the sewing operation and comprises a shuttle body (20) in which a bobbin housing (22) is received for receiving a shuttle thread supply, wherein the thread withdrawal blade (29)

   - may be pivoted between an initial position (Fig. 2) and a thread take-up position (Fig. 4) about a swivel axis (30) parallel to the shuttle axis (23) above the bobbin housing (22),

   - has, in the region of a free end of the thread withdrawal blade (29) that extends counter to the rotational direction (24) during the sewing operation, a thread take-up groove (31) with a base-side cutting edge (32),

   characterised by a free end portion (32c) extended beyond the thread take-up groove (31), the free end position (32c) being rounded in a plan view perpendicular to the moving plane.
2. Thread withdrawal blade according to claim 1, characterised in that the length of the free end portion (32c) is comparable with the length of the take-up groove (31).
3. Thread withdrawal blade according to any one of claims 1 to 2, characterised in that the thread withdrawal blade (29) is arcuate, so it is arranged around the bobbin housing (22) in the assembled initial position.

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