Patent GB-1194967-A (GB)
Title: A Thread Cutting Device for Sewing Machines
IPC: D05B65/06
Filed: 1968-08-02
Abstract: 1,194,967. Sewing machines. VIRGINIO RIMOLDI & CO. 2 Aug., 1968 [20 Sept., 1967], No. 37035/68. Heading D1G. A sewing machine comprises movable threadtension-releasing means and thread-drawing means coupled! operatively to respective pneumatic piston rams, and a single control device for said rams, thread severing taking place during the return strokes of the pistons and thread tension release and drawing talking place during the forward strokes of the pistons. Threads 34, 35, 36 pass to needles 22 via tensioners 30, 31, 32, and respective slots 81 in a plate 80 positioned between a pair of fixed thread guides 45. Plate 80 is rigid with the piston rod 82 of a double-acting pneumatic ram 46. Thread 37 passes to a looper 18 via a tensioner 33 and a hole in the end 89 of the piston rod 90 of a double-acting pneumatic ram 54, end 89 being positioned between a thread take-up cam 53 and a fired thread guide 55. A plate 38, slidable under the tensioners, is rigid with the piston rod 88 of a double-acting pneumatic rams 40, and carries fingers 39 located adjacent the respective pairs of tensioner discs 43 when piston rod 88 is retracted. A thread-cutting blade 56 is rigid with the piston rod 61 of a double-acting pneumatic ram 63 and carries opposed pins 66 engaging respective slots 65 formed' in an upper blade 57 and a lower blade 58, a hooked forward end of blade 56 being enclosed within blades 57, 58 in the retracted position of piston rod 61. The rams are normally supplied with compressed air via a solenoid-operated valve for retracting the piston rods. The machine is operated at full speed by depressing the toe end of a treadle. On release of the treadle the machine is driven slowly until an insulating segment on a slip ring engages a co-operating brush to stop the machine with the needles fully lowered. If it is desired to sever the threads, the heel end of the treadle is depressed to actuate a microswitch, whereby a relay is energised to effect charging of a condenser, and the machine is driven slowly until an insulating segment on a second slip ring engages a co-operating brush. The machine then stops with the needles fully raised, and the condenser discharges through a relay adapted to de-energise the solenoid valve normally supplying air to the rams, and momentarily to energise a solenoid valve supplying air to the opposite ends of the rams, whereby the piston rods advance and again retract. During the advance of piston rod 88, the fingers 39 pass between the discs 43 to release the thread tension. Advance of piston rod 82 serves to draw needle thread from the supply, the slots 81 delaying drawing action until after release of thread tension. Advance of piston rod 90 serves to draw bobbin thread from the supply, a slot in end 89 being unnecessary since the looper thread tension is relatively low. Initial advance of piston rod 61 serves to expose the hooked end of blade 56. Blades 56, 57, 58 then move forwardly together until the threads between the needles and the looper are caught by said hocked end. During the initial part of the return stroke, the threads are severed between said hooked end and blade 57, and the severed ends 78 on the supply side are clamped between blades 56 and 58. Blades 57 and 58 are prevented from moving with blade 56 at the commencement of tihe forward and return strokes by spring-biassed detent means 68. To prevent unthreading of the needles, the severed ends thereat may be clamped between the hooked end 129 of a movable blade 126 and a fixed spring blade 127. Blade 126 is rigid with the piston 'rod 125 of a double-acting pneumatic ram 120 operated in synchronism with the other rams, whereby the severed thread ends are seized by end 129 on the forward stroke of piston rod 125 and are then retracted into clamping engagement with blade 127.