Patent GB-472175-A (GB)
Title: Improvements relating to method and apparatus for slipping stitches
IPC: D05B57/14
Filed: 1936-03-19
Abstract: 472,175. Sewing-machines. PRIME MACHINE CO., Inc. March 19, 1936, No. 8289. Convention date, April 19, 1935. [Class 112] The needle-thread of a lock stitching machine is governed so that a predetermined number of stitches are dropped at predetermined intervals by mechanism which pulls the needle-thread taut so preventing formation of a needle-thread loop for entry by the loop taker. The invention is applicable to machines for sewing plies of material together, the places where stitches are dropped being reserved for the attachment of fastener elements. A similar machine is described in Specification 470,708. In the form shown, the needle 3, presser P, feed dog R and rotating hook B are constructed and operated as is usual in lock-stitching machines. The mechanism for gripping and pulling the needle thread to prevent the formation of the needle loop L, Fig. 14, for entry by the hook 8, includes a gripper G with jaws 10, 11, Figs 3 and 7, the jaw 10 being fixed to the hollow shaft 12 mounted on the machine and the other jaw 11 being mounted on a rod 14 sliding in the shaft 12 and adjustably screwed into a lever 16 pivoted on a rod 17 in the machine arm. The rod 17 is connected to a lever 18 with a roller 19 tracking a cam 20. The needle thread passes between the jaws 10, 11 which are normally brought together by a spring 21 connected to a pin 22 fixed to the jaw 11 and slidable through the jaw 10. The pin 22 causes the jaws to swing together about the axis of the shaft 12. The jaws are oscillated in timed relation with the drive shaft D and the needle bar by an eccentric 23, a roller 32, lever 31 pivoted to the machine frame and link 34 pivoted to a crank arm 35 on the tubular shaft. The eccentric is so shaped that the thread gripper occupies its uppermost position when the needle is in its uppermost position and is swung downwards synchronously with the movement of the thread T. The jaws 10, 11 are actuated towards and from each other to grip and release the thread by the cam 20 which actuates the follower lever 18, lever 16 and rod 14. This cam is mounted on a vertical shaft 24 working in bearings in the machine and driven by a worm gear at a reduced speed from the shaft D'. One stitch is made per revolution of the shaft D. The cam 20 may revolve once for a given number of stitches, say twelve. For each rotation of the cam 20, a stitch is dropped, so that one stitch is missed after everv eleven continuous stitches. For this purpose, a recess 28 comes opposite the roller 19, at every complete rotation of the cam. This causes the jaws 10, 11 to close and grip the thread and as the jaws move, to pull the thread so as to prevent the formation of the loop L, i.e. to pull the thread as shown in Fig. 15, so that the hook 8 cannot enter, so preventing the formation of a stitch. The roller 32 may be held out of contact with the eccentric 23 till a stitch is to be dropped by a roller 30 riding along the top edge of the cam 20. When a stitch is to be dropped, the roller 30 drops into a recess 133, so allowing the roller 32 to contact the cam 23. The stitch-dropping grippers are thrown out of action by moving a lever 40 pivoted at 41 to the machine. This lever pushes a slide 43 under the extension 44 of the rod 31 and lifts this to disconnect the roller 32 from the eccentric 23. The lever 40 may also have a lug for engaging the follower 19 to hold this out of engagement with the cam 20. In the form shown in Fig. 26, the jaws 10, 11 are opened by the wedge end 61 of a fixed block on the uppermost position. When the roller 65 engages the notch 64 in the cam 63, the jaws drop and grip the thread and lift it to prevent the formation of the needle loop as before, so dropping a stitch. Seams. When two plies of material 70, 71 are seamed in this way, with dropped stitches 74 at intervals, Figs. 33, 34, the fastener elements 76, such as hooks, of a fastener tape 75, may be pushed through the places where the stitches have been dropped and secured in this position by stitching the tape to the plies 70, 71. Feed. To render feeding uniform, a pair of rollers 80, 81 co-operate with the usual feed dog R. The roller 81 is mounted on a frame 840 pressed to the work by a spring 842.