The present invention relates to a thread take-off device of a sewing machine arranged in front of the thread tightener for pulling off a predetermined amount of thread from the needle thread reservoir.
Thread take-off devices of this type, which make available sufficient slack thread between the thread reservoir and the thread tightener to prevent, during stitch formation, a tensioning of the thread between the reservoir and the thread tightener are well known in the art, as shown for example, in Swiss Pat. No. 389,374. A disadvantage in these types of devices is that the operator must deliberately guide the needle thread through the thread take-off device during the threading of the machine. The thread must be deflected several times during this procedure and must be inserted in special guide means. Thus, the operation of the machine becomes complicated, and the thread is furthermore placed under a relatively great stress. Additionally, the conventional devices are relatively expensive and poorly suited for the installed thread tighteners.
Sewing machines are known wherein the needle thread is guided from the storage spool arranged at the top in the area of the back side of the machine to a deflecting eye, from where the thread travels through a transverse slot in the arm lid in the forward direction and via an installed thread tightener to the take-up lever at the front side of the machine. The insertion of the thread is especially simple in this type of construction.
To avoid the aforementioned disadvantages of the conventional arrangements, the thread take-off device of the present invention is characterized in that a take-off lever is provided in the area of the thread path leading to the thread tightener. The take-off lever oscillates at right angles to the thread path and in synchronism with the take-up lever and is operated, while intersecting the thread path, against a spring force produced by the control arm of the take-up lever.
In contrast to conventional arrangements, the thread take-off lever is thus associated with the existing thread path, and no additional guide operations and/or threading operations of any kind are required.