Method and device for ensuring loop formation of the needle thread for a shuttle embroidery machine

Abstract

A holder (19) is used to press the stitching base (15) against the stitch plate (17) during the first forward stroke of the needle (3) before returning at the first reversal point and holds it in place during loop formation between the stitch plate (17) and the eye (3") of the needle (3) so that the stitching base (15) cannot be lifted by the retracting needle (3), thereby preventing the loop.

Description

[0001] The invention relates to a method for ensuring the loop formation of the needle thread on a shuttle-type large embroidery machine according to the preamble of patent claim 1 and to a device for ensuring the loop formation of the needle thread for a shuttle-type embroidery machine according to the preamble of patent claim 5.

[0002] When producing embroidery on an embroidery base with appliquéd, sometimes very stretchy fabrics or embroidery where large areas are embroidered using drill holes, i.e. punched or cut-out areas of the embroidery base, the problem is that on the one hand the appliqués cannot be held taut enough to ensure they lie fully on the embroidery base. On the other hand the embroidery base cannot be retightened as required after drilling large cutouts because the missing weft and warp threads in the area of ​​the cutouts results in the taut embroidery base becoming loose. The lack of tension in the appliqués or warp threads in the area around the cutouts causes the taut embroidery base to loosen.of the embroidery base with large cutouts there is a latent risk that the appliqué and possibly also the embroidery base will lift off the needle hole plate in the axial direction of the needle when the needle is pulled back to form the loop, and consequently the formation of a loop large enough for the shuttle to pass through is not guaranteed. Skipped stitches are therefore common. These embroidery errors caused by dropped stitches lead to waste. The main reason for these dropped stitches is that the needle thread is not sufficiently positioned through the embroidery base when the needle is pulled back to form the loop, but rather the thread in the embroidery base lifts the embroidery base off the needle hole plate and therefore only a loop that is too small or no loop at all can form between the needle eye and the embroidery hole, and consequently the needle thread cannot be knotted with the shuttle thread.

[0003] A method according to the preamble of claim 1 and a device according to the preamble of claim 5 are known from DE 10 2008 035 434 A1. EP 0040333 A2 and WO 8703628 A1 disclose spring-loaded hold-down devices.

[0004] An object of the present invention is to provide a method and a device with which the lifting of the embroidery base with the returning needle can be prevented between the fabric presser paws and as a result the distance, ie the distance from the needle eye to the embroidery base, can be reliably shortened and the formation of a thread loop can be ensured.

[0005] These objects are achieved by a method according to the features of claim 1 and a device according to the features of claim 5.

[0006] With this process, when the needle is inserted into the appliqué and the embroidery base, a spring-loaded hold-down device is moved towards the embroidery base and the needle hole plate until the hold-down device comes into contact with the embroidery base and / or the appliqué on the embroidery base. As the needle insertion process continues and the hold-down device comes to a standstill because it is resting on the appliqué and the embroidery base, the contact pressure of the hold-down device is increased and remains so even after the needle stroke is reversed at the first reversal point and during the partial retraction of the needle to form the loop of the needle thread between the needle eye and the embroidery base. The embroidery base is thus held pressed against the needle hole plate by the hold-down device at least until the shuttle moves into the formed loop.

[0007] By locally pressing the appliqué onto the backing, or the backing in the case of large cutouts, directly onto the needle hole plate, after the needle has already pierced the appliqué and the backing, but before the needle stroke reversal begins, the hold-down device ensures that the backing and / or appliqué does not lift from the backing plate when the needle retracts, thus preventing the distance between the needle eye and the backing from becoming shorter. By holding and pressing the backing in place, the loop necessary for the shuttle to pass through is created between the eye and the backing when the needle is retracted.The direct passage of the shuttle through the loop formed after the loop has been formed and the subsequent release of the pressure of the hold-down device on the appliqué and the embroidery base means that immediately after the needle point has left the embroidery base, the stitch base can be moved smoothly and unhindered across the needle axis above the needle hole plate for the next stitch formation. By lifting the hold-down device from the surface of the embroidery base or an appliqué applied to it or an accumulation of satin stitches in particular, the embroidery base can be moved unhindered relative to the needle and to the hold-down device located above it at a distance from the embroidery base. It can also be prevented that the hold-down device hooks onto the recess or engages under it when embroidering around large drilled holes (recesses).

[0008] A spring-loaded hold-down device requires no separate drive. It is forced along directly or indirectly by the needle plunger, to which the hold-down device may be attached, and exerts the necessary contact pressure on the surface of the embroidery base by the needle plunger, which continues to move after contact with the embroidery base. The release of the contact pressure on the embroidery base only ends after the forced loop has formed, by retracting the needle, without any necessary control means.

[0009] The hold-down device comprises a spring designed to provide the necessary contact force, which can be pressed against the needle hole plate. No other moving mechanical parts are required. The hold-down device can be attached to the needle plunger or indirectly driven by it. When not needed, the hold-down device can be easily removed. Alternatively, the hold-down device can, of course, also be operated by a dedicated drive element independent of the needle drive.

[0010] In a first embodiment of the invention, the hold-down device comprises a U-shaped spring profile, the first leg end of which is attached to the needle plunger and the end of the second leg of which includes a bore or recess through which the needle can be passed. By bringing the free second leg of the spring closer to the needle hole plate, the angle between the two spring legs is reduced and the contact pressure on the embroidery base and the appliqué is increased.

[0011] In a further embodiment, the hold-down device has a V-shape and comprises two spring plate sections connected to one another, e.g. by rivets.

[0012] In the second embodiment of the hold-down device, it can also be diamond-shaped, i.e. constructed from two symmetrically arranged V-shaped spring sections.

[0013] In a third advantageous embodiment of the V-shaped hold-down device, one of the two legs is designed as a parallelogram in order to optimize the guidance of the second leg.

[0014] In the fourth embodiment of the invention, two guide rods are arranged on the needle plunger, which are movable relative to the needle plunger. Their ends are connected to each other on the needle side by a pressure plate. The rear ends of the rods are mounted axially displaceably in at least one support. Springs are arranged on the guide rods between the pressure plate and the at least one guide plate attached to the needle plunger. These springs press the pressure plate resiliently against the needle hole plate when the pressure plate rests on the embroidery base and the needle hole plate.

[0015] In the fifth embodiment of the hold-down device, it comprises a single profiled open or closed spring steel ring which is connected to the needle plunger and oppositely comprises a recess for the needle.

[0016] The invention is described in more detail using illustrated embodiments. They show: Figure 1a a partial view of the front end of a needle plunger with inserted needle, a drill and a hold-down device on an embroidery machine in the rest position, Figure 1b the arrangement according to Figur 1a with needle partially advanced into the embroidery base and into the needle hole plate shortly before the first reversal point of the needle, Figure 1c a partial view of a needle pusher with inserted needle, a drill and a hold-down device on an embroidery machine with the needle fully retracted into the embroidery base at the second reversal point, Figure 2a the same arrangement as in Figur 1a, but in a further diamond-shaped design of the hold-down device in clamped state, Figure 2b a perspective view of the hold-down device in Figur 2a , Figure 3a a detailed view of a hold-down device with a parallelogram arm and a simple spring arm, Figure 3b a perspective view of the hold-down device in Figur 3a , Figure 4a another embodiment of the hold-down device with a parallel guided pressure plate, Figure 4b a perspective view of the hold-down device in Figur 4a , Figure 5a shows a further embodiment of the hold-down device comprising a spring profile bent as a ring, Figure 5b shows a perspective view of the hold-down device in Figur 5a , Figure 6 a path / time diagram of the needle movement and Figure 7 a section through the needle hole plate, the embroidery base, the needle and a shuttle.

[0017] In the figures, the arrangement of the individual elements of the device corresponds to that which is usual for large embroidery machines.

[0018] The fabric presser assembly 1 for an embroidery machine comprises a needle 3 attached to the end of a drivable needle plunger 5. In the figures, a drill 7 is clamped below the needle 3 in a drill holder 9, which is designed to create recesses. Furthermore, a fabric paw 11 is shown in the figures. The fabric paws 11 are each arranged between two adjacent needles 3 and, if present, between the needles and drills 7. The fabric paws 11 or their front ends are offset from the axes of the adjacent needles 3, which are arranged on a straight line. The fabric paws 11 are therefore spaced apart from the axes of the needles 3 in both the vertical and horizontal directions.

[0019] Reference number 17 designates the needle hole plate under an embroidery base 15 arranged thereon with an appliqué lying thereon (application not shown visibly).

[0020] The needle 3 in Figur 1a is located at the rear reversal point, i.e. in the rearmost position and with the tip 3' of the needle 3 at the greatest distance from the needle hole plate 17.

[0021] In the first embodiment, a U-shaped hold-down device 19 is attached to the front end of the needle plunger 5. This comprises a spring steel profile, e.g., a spring steel strip, one end of which is connected to the needle plunger 5 and the other end of which is perforated for the passage of the needle 3. The attachment to the needle plunger 5 is free of play and can be achieved by means of a clamping screw or the like. The hold-down device 19 according to the first embodiment ( Figuren 1a bis 1c) thus comprises a curved leaf spring with a recess at its free end 21 through which the needle 3 is passed. The free end 21 encloses the needle 3 with some clearance.

[0022] In Figur 1b the needle 3 has been moved forward by an amount of a and now penetrates an appliqué, the embroidery base 15, and the needle hole plate 17. Along with the needle 3, the paws 11 have also been moved forward, and the sole of their foot 23 is at a distance d from the surface of the needle hole plate. The front end 21 of the hold-down device 19 touches the surface of the embroidery base 13 or an appliqué lying thereon, without the hold-down device 19 being significantly deformed. The needle point 3' and the needle eye 3" are now completely behind the needle hole plate 17. The needle movement is not yet complete.

[0023] After the needle movement is reversed at the beginning of the first leftward stroke "F", the embroidery base 15 continues to be pressed against the surface of the needle hole plate 17 by the hold-down device 19. This prevents the needle thread 35 guided through the embroidery base 15 from subsequently retracting to the right in synchronization with the needle 3. As a result, a thread loop 37 ( Figur 7 ). Now, the tip of a shuttle 39 with the shuttle thread 41 can enter the loop 37 and pass through it. As soon as the tip of the shuttle 39 has penetrated the loop 37, the loop 37 of the needle thread 35 is further opened by the second stroke "H" of the needle 3, thus allowing the passage of the shuttle 39.

[0024] In Figur 1cThe needle 3 has advanced further by the amount a plus x, and the hold-down device 19, or its two ends, have moved closer together. Since the hold-down device 19 is made of spring steel, its free end 21 now presses the embroidery base 15 onto the surface of the needle hole plate 17 and holds it in place. The paw 11, driven independently of the needle 3, remains permanently at a distance d from the surface of the needle hole plate 17.

[0025] After the second reversal point, when the needle eye 3" and the needle tip 3' leave the embroidery base 15, the front end 21 of the hold-down device 19 returns to its basic position. The hold-down device 19 is thus lifted off the embroidery base 15 so that it can be moved essentially frictionlessly on the needle hole plate 17 for the next stitch. The paw 11 is also lifted so as not to hinder the movement of the embroidery base 15.

[0026] By temporarily pressing the embroidery base 15 in the area around the needle 3, it can be ensured that a thread loop 37 of a size is formed which can be safely grasped or penetrated by the shuttle 39.

[0027] The fastening of the hold-down device 19 directly to the needle plunger 5 ensures that the beginning of the pressing of the embroidery base 15 against the needle hole plate 17 always takes place at exactly the right time and also its subsequent lifting.

[0028] In the second embodiment of the hold-down device 19 according to Figuren 2a and 2bThis comprises four leaf spring elements which form a diamond and are connected to one another at their widest point by rivets 25 or other means. The leaf spring elements in front of and behind the connection points can each consist of legs connected to one another. The V-shaped areas in the area of ​​the rivets are mirror-symmetrical to the needle axis and ensure that the recess for the needle 3 in the area of ​​the tip of the V-shaped parts always remains in the axis of the needle 3 in every position, i.e. tensioned and untensioned. A displacement parallel to the embroidery base 15 during pressing and relaxing therefore does not occur.

[0029] In a third embodiment of the hold-down device 19 according to Figuren 3a and 3b , in which again as in the Figuren 1a bis 1cthe hold-down device 19 is arranged only on one side of the needle axis, a vertical displacement of the front end 21 of the hold-down device 19, i.e. displacement parallel to the stitch lock plate, during pressing is reduced in that the rear legs 19' are designed as a parallelogram and comprise two rear legs 19' connected at their ends, which are connected to one another at their ends by spacers 20.

[0030] In the fourth embodiment of the hold-down device 19 according to Figur 4a and 4b This comprises two guide rods 33 running axially parallel to the needle 3, which are slidably guided in a carrier 31 with the needle plunger 5, and on each of which a helical spring 27 is mounted, which holds a pressure plate 29 guided parallel to the needle axis. As in the other embodiments, the pressure plate 29 is provided with a central recess through which the needle 3 passes.

[0031] The two spaced-apart, parallel guide rods 33 are guided axially displaceably on the carrier 31. For this purpose, corresponding bores are provided in the carrier 31. In a preferred embodiment, the carrier 31 comprises two spaced-apart plates, so that a relatively long guide path for the guide rods 33 can be achieved. The carrier 31 is preferably removably connected to the needle plunger 5. The two coil springs 27 are held slightly tensioned on the guide rods 33 between the pressure plate 29 and the carrier 31.

[0032] During embroidery, the pressure plate 29, as in the first-mentioned examples, comes into contact with the embroidery base and any appliqué lying thereon and presses it against the surface of the needle hole plate 17. The pressure plate 29 is consequently precisely guided by the precise guide in the carrier 31 and is held exactly parallel to the needle hole plate 17 when pressed onto the embroidery base.

[0033] In a fifth embodiment of the presser arrangement ( Figuren 5a and 5b ) the fabric presser (19) comprises a ring-shaped leaf spring profile, which, like the design in Figur 2 is connected to the needle plunger 5 and includes a recess for the needle 3. In the rearmost position of the needle plunger, the fabric presser 19 appears circular or already slightly oval, in the frontmost position of the needle the oval is compressed to such an extent that a contact force is generated on the embroidery base 15, which lies on the needle hole plate 17.

[0034] A symbolic representation (stroke / time diagram) shows that to form a thread loop 37, the hold-down device 19 reaches the embroidery base 15 at time (E). Then, until the stroke is reversed (F), the contact pressure is increased. Upon retraction of the needle in the area of ​​the crossed hatching up to (G), a secure loop formation can occur. The contact pressure on the embroidery base 15 is maintained until the needle has left the embroidery base after the second stroke according to (J).

[0035] In the Figur 7 illustrates how the shuttle 39 or its tip grasps the thread loop 37.

[0036] As an alternative to fastening the hold-down device 19 to the needle plunger 5, the hold-down device 19 can also be pressed onto the embroidery base by a separate plunger or drive (not shown).

Claims

1. A method on a shuttle embroidery machine, equipped with a needle plate (17) and with presser feet (11) arranged next to a needle (3), for ensuring loop formation when embroidering elastic embroidery bases (15), embroidery bases (15) having ornaments or embroidery bases (15) having recesses created by drills, which are to be embroidered around in the embroidery base (15), characterized by the following steps: - inserting the needle (3) into the embroidery base (15) and introducing an elastically configured, displaceable holder (19) arranged between the presser feet (11) and surrounding the needle, until the holder (19) makes contact with the embroidery base (15) or the ornament on the embroidery base (15), - continuing the insertion process of the needle (3) at the same time as the holder (19) is stopped on the ornament or the embroidery base (15) and increasing the contact force on the embroidery base (15) by built-up spring tension, - reversing the stroke of the needle (3) at a front reversal point and partially withdrawing the needle (3) to form a loop of the needle thread between the eye (3") of the needle and the embroidery base (15), which is pressed by the spring-loaded holder (19) on the needle plate (17), and - moving the shuttle (39) into the thread loop, - further withdrawing the needle (3) from the embroidery base (15) and lifting the holder (19) off the surface of the embroidery base (15), wherein - the method is designed to prevent the embroidery base from lifting along with the retracting needle between the presser feet (11).

2. The method according to Claim 1, characterized in that the holder (19) is introduced directly or indirectly to the embroidery base (15) by the needle bar (5) or by a feed element driven independently of the needle bar and is temporarily pressed onto the embroidery base (15).

3. The method according to Claim 2, characterized in that, after the thread loop (37) has been captured by the shuttle, the pressing of the holder (19) onto the embroidery base (15) by the needle bar (5) or a feed element is ended.

4. The method according to Claim 3, characterized in that the ending of the pressing-on force of the holder (19) is carried out by withdrawing and lifting the holder.

5. A device for a shuttle embroidery machine for ensuring loop formation when embroidering elastic embroidery bases (15), embroidery bases (15) having ornaments or embroidery bases (15) having large-area recesses created by drills, which are to be embroidered around in the embroidery base (15), wherein the embroidery machine comprises on the needle side a needle plate (17), a drivable needle (3) which is held in the needle bar (5) of the embroidery machine and presser feet (11) arranged next to the needle (3) and a shuttle race, characterized in that the device is configured as an elastically configured, displaceable holder (19) which can be arranged between the presser feet (11) and surrounding the needle (3), and the holder is further designed such that the holder (19) arranged between the presser feet (11) and surrounding the needle (3), on insertion of the needle (3) into the embroidery base (15), is introduced until the holder (19) makes contact with the embroidery base (15) or the ornament on the embroidery base (15) and the holder (19) is stopped on the ornament or the embroidery base (15) at the same time as the insertion process of the needle (3) continues and the contact force on the embroidery base (15) is increased by built-up spring tension and on reversing the stroke of the needle (3) at a front reversal point and partially withdrawing the needle (3) to form a loop of the needle thread between the eye (3") of the needle and the embroidery base (15), the embroidery base (15) is pressed by the spring-loaded holder (19) on the needle plate (17) and after the shuttle (3) moves into the thread loop during the further withdrawal of the needle (3) from the embroidery base (15), the holder (19) is lifted off the surface of the embroidery base so that the embroidery base is prevented from lifting along with the retracting needle between the presser feet (11).

6. The device according to Claim 5, characterized in that the holder (19) can be carried by the needle bar (5) and can be moved along with the needle (3).

7. The device according to any one of Claims 5 or 6, characterized in that the holder (19) comprises a spring plate configured in a U-shape or a V-shape, the first end of which can be fastened to the needle bar (5) and the second end of which has a recess through which the needle (3) can be moved relative thereto.

8. The device according to Claim 7, characterized in that the legs (19') of the spring plate are riveted together.

9. The device according to Claim 8, characterized in that one leg of the spring plate comprises two parallel rear legs (19') made of spring plate, which are kept spaced apart by spacers (20).

10. The device according to any one of Claims 5 or 6, characterized in that the holder (19) comprises two guide rods (33) which are displaceably guided in a support (31) which can be fastened to the needle bar (5) of the embroidery machine and in that the ends of the guide rods (27) are connected by a pressure plate (29) and in that the pressure plate (29) and guide rods (33) can be displaced against spring force relative to the support (31).

11. The device according to Claim 10, characterized in that the spring force can be produced by a spring (27) inserted between the pressure plate (29) and the support (31).

12. The device according to Claim 11, characterized in that a spring (27) is arranged on at least one of the guide rods (33).

13. The device according to Claim 5, characterized in that the holder (19) can be actuated by a drive independent of the drive of the needle bar (5).

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