Patent GB-1041124-A (GB)
Title: Improvements in or relating to sewing machine electric driving means
IPC: D05B69/10
Filed: 1964-06-25
Abstract: 1,041,124. Sewing machines. HUSQVARNA VAPERFABRIKS A.B. June 25, 1964 [July 1, 1963], No. 26295/64. Heading D1G. A sewing machine comprises two movable co-operating working means one of which is driven by a pulse motor, and the other of which is associated with a break-contact-free pulse generator having a pulse emitter and an exciting means movable in synchronism with said other working means and connected to an electronic control assembly adapted to transform said pulses to current pulses for driving the first-mentioned working means in synchronism with the other working means. As shown, the rotary looptaker 14 of a sewing machine is driven via a shaft 15 by a variable speed motor 16 connected to electric supply terminals A and C. A pulse generator, associated with the looptaker, comprises an exciting means in the form of a permanent magnet 28 carried by a rotary member 26 driven by shaft 15, and an emitter in the form of an iron-cored coil 27 generating an electric pulse at each revolution of member 26. The head 3 of the machine carries a permanent magnet 4 formed with an annular recess 5 adapted to receive a solenoid coil 6 mounted on a non-magnetic needle bar 8 slidable in bearings 11 carried by magnet 4. The stroke of the needle bar is limited by rubber stops 12, 13 adjustably mounted thereon for co-operation with the bearings 11. Coil 27 is connected to an input circuit 19 of a control assembly, one lead 17 from coil 6 is connected to the junction between a pair of series-connected transistors an in output circuit 20 of the control assembly, the other lead 18 from coil 6 is connected to a mid terminal B of the electric supply, and the terminals A and C are connected to the respective transistors. The arrangement is such that when the looptaker 14 is stationary, current supplied to coil 6 via one transistor serves to bias the needle bar to the raised position, and when the looptaker rotates, each pulse generated in coil 27 serves to reverse the conductivity of the transistors, whereby coil 6 receives a pulse of current in the reverse direction to lower the needle bar, which thereby reciprocates in synchronism with the looptaker. Member 26 is driven by 2 to 1 reduction gearing if the looptaker rotates twice for each stitch-forming cycle, magnet 28 may be incorporated in the looptaker. Downward movement of the needle bar is adapted to produce operative movement of the thread take-up 51 and the feed dog 40, whereby, if the needle bar does not descend fully, the take-up and feeding strokes are suppressed. Coils 46 and 53, associated with respective permanent magnets 45 and 52, are mounted co-axially about the needle bar, whereby an iron member 47 fitted to the top of the needle bar produces electric pulses in said coils on full descent of the needle bar. Coil 46 is connected by a lead 71 to a circuit 59 adapted, on receiving a pulse from coil 46, to render a transistor 65a conductive, and thereby energize a rotary magnet 50, via leads 67, 68, to actuate a thread take-up 51 against spring bias. The feed dog 40 is carried by a feed bar 40a which receives feed-lift motion from a cam 41 on shaft 15. A spring 48, connected to one end of the feed bar, biases the latter against a fixed stop 60. The other end of the feed bar constitutes the armature of a solenoid coil 42 which is connected by a leaf spring 42a to a non rotary nut 43 movable linearly by means of a screw 44. A pulse in coil 53 is transmitted via a lead, 64 to a circuit 49 adapted thereby to render a transistor 65b conductive for energizing coil 42 via leads 69, 70 to effect a feed-advance stroke against the bias of spring 48. The length of the stroke is governed by a stop 61 in coil 42, the position of the latter being adjustable by screw 44. It is stated that pulses may be transmitted by means of a light-sensitive cell and a rotary shutter. Alternatively, shaft 15 may drive a multipermanent magnetic-pole rotor co-operating with a stator to transmit pulses to the stator of a multi-permanent magnetic-pole rotor coupled mechanically to the needle bar for drawing the latter step-wise.