EP0008615A1 - Needle thread controlling device mounted under the throat plate of a lockstitch sewing machine - Google Patents

Abstract

Lockstitch sewing machine with a rotating lockstitch looper (2) and a spring bar (1) arranged in the space between the needle plate (7) and the hook (2) to influence the movement of the needle thread loop (3).

Description

The invention relates to a lockstitch sewing machine with a rotating hook and a bobbin case with an embedded hook thread bobbin, as well as a device for influencing the movement of the needle thread loop during the stitch tightening.

A sewing machine of the type mentioned is known from German patent 422 546. In order to influence the movement of the needle thread loop, in this machine a leaf spring is provided on the bobbin case fastening, which interacts with a nose of the bobbin case. As a result, the needle thread loop is held in place and clamped briefly, the spring tensioning. After the pinch is released due to the thread tightening, the spring swings. the loop pulled together to a small diameter against the underside of the material. This largely prevents the formation of the known unsightly nodules, the so-called dolls, which are particularly evident on the underside of the fabric in the case of heavily twisted yarns. A spring with a similar effect is proposed in German patent application P 27 41 830.0.

Thereafter, a spring rod clamped at one end, as the gripper counter tip, picks up the needle thread loop thrown off by the actual gripper tip, holds it back briefly and then also lets it snap off as a result of the further movement of the gripper. These two devices for influencing the needle thread loop make it contract to a relatively small diameter, so that there is only little space left for the formation of the undesirable "dolls". These devices for influencing the needle thread loop require for their perfect function that the tensions acting on the needle thread loop and on the looper thread wrapped around it have a balanced ratio, as is the case in conventional sewing applications with a normal lockstitch intertwined in the middle of the fabric. However, if the needle thread tension is set weaker relative to the looper thread tension, then the heavily tensioned looper thread, which is wrapped by the needle thread loop under weak tension, hinders the desired “jump effect” with which the loop is bounced against the underside of the fabric. Such applications of a so-called "raised seam" are, for example, embroidery work with a lockstitch sewing machine, if the embroidered patterns are to emerge plastically from the surface of the fabric, and also the sewing of buttonholes according to the method according to German patent 739 559.

The invention has for its technical object to provide a device for influencing the movement of the needle thread loop, which works equally safely even with abnormal thread tension conditions.

The invention solves this technical problem by features set out in the main claim; further advantageous features of the invention are set out in the subclaims.

• Fig. 1 zeigt einen Doppelsteppstichgreifer in Seitenansicht mit einem Abschnitt der Stichplatte sowie mit zwei aufgelegten Stoffzuschnittlagen, die mittels einer sogenannten hochgezogenen Doppelsteppstichnaht zusammengenäht werden; im Bewegungsweg der von der Greiferspitze abgeworfenen Nadelfadenschleife liegt als eine Einrichtung zur Beeinflussung derselben ein Federstab 1;
• Fig. 2 ist die Unteransicht der Stichplatte gemäß Fig. 1 mit dem Federstab 1 und seinen Befestigungselementen an der Stichplatte.

The accompanying drawings illustrate an embodiment of the invention, which is described in detail in the text below.

• Fig. 1 shows a double lockstitch looper in side view with a portion of the needle plate and with two fabric cut layers placed on it, which are sewn together by means of a so-called double lockstitch seam; In the path of movement of the needle thread loop thrown off the hook tip there is a spring bar 1 as a device for influencing the same;
• Fig. 2 is the bottom view of the needle plate according to FIG. 1 with the spring bar 1 and its fasteners on the needle plate.

Gripper 2 in Fig. 1 is a rotating gripper of conventional design in the horizontal shaft design, which belongs to a lockstitch sewing machine, not shown, also of known construction. The needle thread loop 3 - after it has been guided around the hook 2 in the usual manner with the hook thread 4 emerging from the housing of the hook 2 - being thrown off the invisible tip thereof. The needle thread loop 3 is - as is known - under the influence of a conventional thread lever, not shown, during the stitch tightening phase and moves upward with the looped looper thread 4 until its movement is stopped by a spring bar 1.

The spring bar 1 bent at its ends in a U-shape is held in the clamping blocks 5 and 5 'fastened to the underside of the throat plate 7 (FIG. 2) shown in detail with the clamping screws 6 and 6'. The clamping blocks 5 and 5 'are arranged such that the spring bar 1 is directed transversely to the material feed direction NV and can also be displaced in this direction. This takes place from the extended position shown in the drawings with solid lines to the bent position shown further to the right, shown in dash-dot lines.

Such a displacement occurs when the needle thread loop 3 reaches the spring bar 1 during its upward movement after leaving the hook 2, the hook thread 4, which is tensioned more than the needle thread loop 3, acting restrained on the loop. In this way there is a brief lingering of the loop under the spring bar 1 (Fig. 1). The thread tension, which continues to act, causes the needle thread loop 3 to stretch, so that any nodules formed on the path from the gripper 2 to the spring bar 1 are loosened. The spring rod 1 is now displaced into the aforementioned bent position by the further movement of the loop. After the needle thread loop 3, which has been pulled further upward, has passed the plane of movement of the spring bar 1, the spring springs back into its extended starting position. The needle thread loop 3 now only covers the short distance to the fabric, where - as mentioned - the threading of the needle and looper threads takes place on the underside of the fabric. The result is a clean and error-free seam pattern that was previously unknown in sewing applications with a "raised seam", as nodules tend to appear here due to the uneven tension ratio. The extremely short path between the spring bar attached under the needle plate to the fabric also has a positive effect, since the uncontrolled movement of the needle thread loop between spring bar 1 and fabric has been reduced to a minimum.

The invention is not limited to the exemplary embodiment described; there are numerous other designs and attachments of the spring rod, e.g. as a one-sided clamp, possible.

The application of the invention will mainly extend to sewing applications with different thread tension ratios; however, improvement of the seam appearance of a conventional lockstitch seam by means of the invention is also conceivable.

Claims (2)

1. lockstitch sewing machine with a rotating hook and a bobbin case with embedded hook thread bobbin, and with a device for influencing the movement of the needle thread loop during the stitch tightening, characterized in that in the range of motion of the needle thread loop (3) in the space between the needle plate (7) and the Gripper (2) is arranged a spring bar (1) which temporarily stops the needle thread loop (3). 2. lockstitch sewing machine according to claim 1, characterized in that on the underside of the throat plate (1) two clamping blocks (5,5 ') are provided for holding the ends of the spring bar (1) and that the same from a first extended position - with short holding the needle thread loop (3), with the cooperation of the looper thread (4) wrapped by the same, is displaceably attached to a second bent position that releases the needle thread loop (3).

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