Thread-cutting device for an eyelet buttonhole sewing machine

#The present invention relates to a thread-cutting device for an eyelet buttonhole sewing machine according to the preamble of claim 1.

#An eyelet buttonhole sewing machine of the generic type became known as Exhibit 30 at the IMB Fair of 1997 in Cologne as D{umlaut over (u)}rkopp Adler Class 578-113221 E831 (recently designated as Cl. 578-113221 E1831), with which a stitch row is produced which is designed in the shape of a zig-zag and in alternating fashion as a single chain and double chain stitch seam. The eyelet buttonhole sewing machine includes rotatable sewing tools, including a rotatable looper support arranged below the support for the material to be sewn. It is possible to rotate the sewing tools and the looper support about an axis extending parallel to the longitudinal axis of the sewing needle. A thread cutter is arranged on the rotary looper support and is constructed with one thread-cutting tool for the needle thread and with another thread-cutting tool for the looper thread. Each thread-cutting tool can be moved independently of the other and may be operated via separate drives. Required movements for the thread-cutting tools are initiated by producing the drive connection from the thread-cutting tools to the drives arranged in a stationary fashion on the sewing machine frame in a defined rotary position of the looper support. Consequently, the thread-cutting device and/or the individual thread-cutting tools can be driven only subsequently, thus lengthening the machine cycle.

#In principle, movement is initiated for a thread cutter of an eyelet buttonhole sewing machine as disclosed in DE-C 631 138.

#FIG. 1 shows an elevational view of a part of an eyelet buttonhole sewing machine,

#FIG. 2 shows an elevational view of a part of the machine of FIG. 1 on an enlarged scale,

#FIG. 3 shows a view of the part in FIG. 2, in the direction of the viewing arrow III in FIG. 2,

#An eyelet buttonhole sewing machine 1 has conventional features, includes an arm 2, a frame 3 and a baseplate 4. Drive means (not marked) are provided in the arm 2 for driving a needle bar 5 up and down. The bar, is of tubular construction and is fitted at its lower end 6 with a needle 7. A needle thread 8 is fed from a thread supply (not shown) to the inner bore of the needle bar 5, through which the thread extends. The thread emerges at the lower end 6 of the bar 5, and is guided through the eye of the needle 7.

#The needle bar 5 is held in a bearing 9 in a longitudinally displaceable fashion, and is guided in that bearing with regard to its rotary position. The special configuration of the bearing 9 disclosed in U.S. Pat. No. 1,991,627 further permits the needle bar 5 the possibility of being imparted a swivelling movement.

#Furthermore, a toothed-belt wheel 10 on the bearing 9 is wrapped around by a toothed belt 11. The toothed belt 11 is also wrapped around a toothed belt wheel 12 which is permanently connected to the upper end of a shaft 13. The shaft 13 is rotatably mounted in an upper bearing 14 which is up and close to the arm 2 and in a lower bearing 15 which is in the region of the baseplate 4. A toothed belt wheel 16 is fastened on the shaft 13 below the bearing 15. The wheel 16 is wrapped around by a toothed belt 17. The toothed belt 17 also wraps around a toothed belt wheel 18 which is fastened on a hollow shaft 19. An upper toothed belt drive 20 is formed with the toothed belt wheels 10, 12 and the toothed belt 11. A lower toothed belt drive 21 is formed with the toothed belt wheels 16, 18 and the toothed belt 17. Both toothed belt drives 20, 21 each have a transmission ratio of i=1. Furthermore, toothed wheels 10 and 18 are arranged on an axis 22 that extends vertically. Apart from slight deflection movements, the needle bar 5 extends likewise with the needle 7 on the axis 22.