Patent GB-854250-A (GB)
Title: Improvements in and relating to lockstitch sewing machines
IPC: D05B73/12
Filed: 1958-11-25
Abstract: 854,250. Sewing machines. UNION SPECIAL MACHINE CO. Nov. 25, 1958 [Nov. 27, 1957], No. 37837/58. Class 112 A lock stitch sewing machine comprises a rotary drive shaft coupled to a hook shaft having a rotary hook and rotary component mounted on it, a bobbin carrier journalled in said component and prevented from rotation by a projection on the carrier co-operating with a shoulder on the machine frame and a cam provided adjacent the bobbin carrier to turn the carrier counter to the direction of rotation of the rotary component. Fig. 2 shows the drive shaft 11 coupled, by gear wheels 27 to the two rotary hook units 15, 18 positioned either side of a pair of needles 30, Fig. 6. The unit 15, Fig. 6, comprises a hollow hook shaft 24, journalled in extensions 22, 23 of the frame 21 and carrying at its upper end a rotary hook 28 which is provided with a beak 28a, Fig. 12, adapted to seize a needle thread loop at the appropriate time in a stitch forming cycle. A gear 26 meshes with the spiral gear 27, Fig. 2, and at the lower end of the hook shaft 24 is a sprocket 46 which is connected to a sprocket 47 on the cam shaft 43 by a toothed belt 48. As shown the camshaft rotates at half the speed of the hook shaft but in another embodiment the ratio may be 1:1. Within the rotary hook 28 is mounted a bobbin carrier which is restrained against rotation with the hook body by a projection 35 on the carrier which fits into a gap 36, Fig. 12, provided between downwardly extending ribs 37 and 38 on the undersurface of a throat plate 39 secured to the main frame. Normally the frictional drag tending to rotate the bobbin carrier will urge the projection 35 into engagement with rib 37. Therefore a cam 40 is provided to rotate the bobbin carrier when required counter to the direction of the hook 28 allowing a gap to form between rib 37 and projection 35 for the free passage of the needle thread loop. The timing of the cam 40 attached to the camshaft 43 can be adjusted by slackening screw 47a, Fig. 6, and rotating the camshaft 43 without disturbing sprocket wheels 46 and 47. The unit 18 of the machine is very similar in construction to unit 15 but there is a slightly different relationship between its various parts, for while both hook units rotate in the same direction, one is left handed and the other right handed and operation of the cams move the projections on the bobbin carriers in opposite directions, i.e. one in the direction of feed and the other counter to that direction. This necessitates a slightly different location for the ribs on the throat plate 39. The work feeding mechanism is similar to that disclosed in Specification 724,992. In another embodiment (not shown) the toothed belt 48 between sprocket wheels 46 and 47 is replaced by an idler sprocket. A further embodiment, Fig. 21, has a sprocket wheel 88 for rotating the cam which is driven through a belt 87 by sprocket wheel 86 on a separate shaft 84a driven through gears 82, 83 from the main rotary shaft in the frame independently of the means for driving the rotary hook. In a further embodiment the cam has one step and co-operates with a projection at the top of the bobbin carrier. To enable adjustment of the hook units 94 and 95, Fig. 24, into a position in which they are relatively close to each other, the portion of the feed bar 110 positioned between the hook units is reversely curved at 116.