GB964372A - Improvements in thread trimming device - Google Patents

Abstract

964,372. Sewing machines. AMERICAN SAFETY TABLE CO. Inc. April 16, 1962, No. 14656/62. Heading D1G. In a sewing machine the needle and bobbin threads are automatically severed at the end of a stitching operation by contact with respective electrically-heated elements. A resistance wire 80 crosses the forked portion of the presser foot 29 horizontally at a position to the rear of the path of the needle 22, and is connected to leads 82, 83. The lower part of the needle hole 52 in the throat plate 51 is encircled by a resistance wire 70 connected to leads 72, 73. The needle thread 30, in the needle side of the tensioner 32, passes through the looped end of an arm 45 carried by a rotary solenoid 40. The under thread 56 passes through the looped end of an arm 61 carried by a rotary solenoid 60. The wires 70, 80 may be energized, via a normally open switch 109 and respective rheostats 65, 67, from a secondary winding 94 of a transformer 90. Solenoid 60 may be energized, via a normally open switch 108 and rectifier 95, from a secondary winding 92 of transformer 90. Solenoid 40 may be energized, via a normally open switch 107 and a rectifier 96, from a secondary winding 93 of transformer 90. A motor M is normally connectible to the supply mains 113, 114 through one pole of a two-way switch 106, and normally open switches 122 and 123. The motor drives cams 102, 103, 104, 105 adapted to operate switches 106, 107, 108, 109 respectively. A normally open switch 121, in a circuit 117, 118, is mechanically coupled to switch 122. Switch 123 is arranged to close automatically when the treadle is released to stop the machine. Switches 121,122 are then momentarily closed whereby circuit 117, 118 is energized to actuate means, such as that described in U. S. A. Specification 2,961,591 for positioning the needle in its uppermost position, and motor M is started for driving the cams 102 to 105. Upward movement of the needle is accompanied by a degree of work feed sufficient to carry the needle thread 30 into contact with the wire 80. After the motor has run for 50 milliseconds, cam 102 changes the polarity of switch 106 to establish a holding circuit through the motor. After the lapse of another 100 milliseconds cams 103 and 104 close switches 107 and 108, whereby arm 45 swings to provide slack thread between the needle 22 and the tensioner 32, while arm 61 swings to carry the under thread 56 into contact with the wire 70, cam 103 opening switch 107 after a lapse of 150 milliseconds. 50 milliseconds later cam 105 closes switch 109 for a period of 50 milliseconds, whereby the heated wires 80 and 70 sever the threads 30 and 56 respectively. Cam 104 opens switch 108 ¢ second after the motor has commenced to run, and cam 102 reverses the polarity of switch 106 to stop the motor 1¢ seconds later.