Patent GB-784030-A (GB)
Title: Improvements in or relating to thread severing devices for sewing machines
IPC: D05B65/00
Filed: 1955-12-08
Abstract: 784,030. Sewing machines. PFAFF AKT.-GES. G. M. Dec. 8, 1955 [Dec. 10, 1954], No. 35207/55. Class 112 In a sewing machine provided with a device for severing the needle thread, and a device disposed below the throat plate for severing the lower thread, a vice or clamping means which is displaceable in the feeding direction and which co-operates with the cutter of the upper severing device is releasable by the movement of the needle bar of the machine. A presser foot assembly comprises a body 11 secured to the presser bar, and a presser foot 13 pivoted on body 11. A knife blade 27 fixed to the bottom of the latter has a cutting edge 28 at its front end. A slide 19, movable on plate 27 is provided at its respective ends with a vice jaw 20 and a flange 23. A pin 26, projecting from slide 19 adjacent an oblique thread-receiving slot 22 formed in the latter, is adapted to abut body 11 for limiting rearward movement of slide 19 under the action of compression springs 30 interposed between body 11 and flange 23. A rod 32, provided at its front end with a vice jaw 31, is urged rearwardly by a leaf spring 34. A lever 38, pivoted at 37, is provided at one end with a nose 39 engaging flange 23 and at the other end with a curved cam portion engaged by a roller 43 on a lever 42. One end of the latter is pivoted at 45 within a slot 44, and the other end has attached thereto an operating cable 48. Lugs 53, which project rearwardly from a member 52, are pivoted at 54 within slot 44. A compression spring 63 is interposed between body 11 and the upper part of member 52, and the latter is formed with a vertical slot 55 and a horizontal groove 56 thereabove. A latch member 65, which is also pivoted at 45, is biased outwardly by a spring 69. Slidable pins 59 are interposed between member 52 and flanges 60 on lever 38, and a slidable pin 61 is interposed between member 52 and spring 34. At the completion of sewing, cable 48 is operated to raise lever 42 to the horizontal position, whereby roller 43 rocks lever 38, causing nose 39 to move slide 19 for engaging the needle thread 83 with slot 22, and pins 59 to rock member 52, when spring 69 rocks latch 65 to engage a nose 67 on the latter with groove 56. Member 52 then being clear of pins 61, spring 34 moves rod 32 to close jaw 31 upon jaw 20 to clamp thread 83 therebetween. When cable 48 is released, springs 30 move slide 19 rearwardly, whereby levers 38 and 42 return to their initial positions, and thread 8 is cut between jaw 20 and knife edge 28. Nose 67 remains engaged in groove 56, whereby spring 69 maintains member 52 in the rocked position with a nose 68 on member 52 in the line of movement of needle bar 4, while spring 34 maintains jaw 31 against jaw 20 with the thread clamped therebetween. When sewing is re-commenced, the needle bar pushes nose 68 aside to release nose 67, thereby allowing spring 63 to return member 52 to its original position and thus engage pin 61 to stress spring 34 for moving jaw 31 for releasing the thread end. The undersurface of the throat plate 8 is formed with a groove 72<SP>1</SP> containing a stationary knife (not shown), and a slide 76 pressed upon said knife by a blade spring 77. A pin 78 projects from slide 76 into a slot 79 formed in one arm of a lever 80, to the other arm of which is attached a tension spring 87 and an operating cable 81. The latter is arranged to be operated .simultaneously with cable 48, whereby slide 76 is moved against the bias of spring 87 to engage a hook 75 on said slide with the lower thread 84. When cable 81 is released, hook 75 draws thread 84 under blade 77 and over the knife edge, whereby the thread is severed and the thread end is clamped between blade 77 and slide 76.