Patent GB-768784-A (GB)
Title: Power control units in sewing machines
IPC: D05B69/00
Filed: 1955-04-19
Abstract: 768,784. Sewing machines. SINGER MANUFACTURING CO. April 19, 1955 [May 5, 1954], No. 11228/55. Class 112. In a cyclically-operated sewing machine comprising a work clamp and a stop-motion mechanism, the clamp is adapted to be opened and the mechanism to be moved to the running position by respective power-operated means controlled by respective electricallyoperated means, and one or the other of the latter may be energised by means under control of the attendant. A button sewing machine has a work clamp comprising a lower jaw 32 and an upper jaw 33 pivoted thereto at 34. The lower jaw is slidable in the work-carrying arm 16 of the machine by means of a lever 30 one end of which is engaged in a cam groove provided in a pattern cam 29 carried by a rotary shaft 26. The upper jaw is urged downwardly by a spring-biased plunger 36 slidable in the upper arm 19 of the machine, and may be raised by a link 38 connecting the jaw to a crank 39 carried by a rock shaft 40. A crank 41 on the latter is connected by a link 42 to a vertical push rod 43 mounted in the standard 18 of the machine and biased downwardly by a spring 45. One arm of a bell crank lever 46, pivoted at 47, underlies the push rod, the other arm carrying a depending chain 48, whereby downward movement of the latter serves to raise the push rod and thereby to lift the upper jaw. Starting and stopping gear. Power is transmitted to the main shaft 15 of the machine by a V-belt 50 via a clutch pulley having a fast element 51 and an axially movable element 52, the position of the latter being governed by a leaf spring 53, one end of which is fixed in a bracket 54 and the other end is embraced by the slotted end of a rod 55 carried by a stop-motion control lever 56 pivoted at 57 to a fixed bracket 58. Lever 56 also carries a plunger 59 which is biased to a central position by a pair of opposed springs 60, 61, and which carries at its lower end a block 62 adapted to engage a stop-cam 63 provided on the fast pulley element. Lever 56 also carries an arm 64 connected by a link 65 to a vertical push rod 66 biased downwardly by a spring 67. One arm of a bell crank lever 69 pivoted at 70 underlies the push rod, the other arm carrying a depending chain 71 downward movement of which serves to raise the push rod and thus to rock lever 56 in the clockwise direction, whereby block 62 is disengaged from cam 63 and spring 53 moves element 52 to engage belt 50 with element 51. A spring 76 simultaneously moves the vertical arm of a bell crank lever 74 pivoted at 75 under a shoulder 73 provided on the push rod to hold the latter in the raised position. A cam plate 77 mounted on the rotary pattern cam 29 is provided with a cam surface 78 which co-operates with the horizontal arm of lever 74 near the end of the stitching cycle to move the vertical arm from shoulder 73 to a higher shoulder 72, whereby lever 56 moves to a small extent anti-clockwise to free belt 50 from element 51. On completion of the stitching cycle, a cam surface 79 co-operates with lever 74 to move the latter free from shoulder 72, whereby block 62 is engaged with cam 63 to stop the machine. Chains 48 and 71 are connected respectively to levers 87 and 88 pivoted on a bracket 86, lever 87 being connected to the piston rod 90 of a pneumatic jack 84 and lever 88 being connected to the piston rod 93 of a pneumatic jack 85. The admission of compressed air to the jacks is controlled by electrically-operated valves 95 and 96. The electrical circuit for valve 95 contains a switch 102 and the circuit for valve 96 contains a switch 103, said circuits being connected to a single-pole two-way treadle-operated switch 101, and the latter being controlled by a switch 100. The treadle switch is so arranged that it is biased normally to energise the circuit of valve 95, the switch also having a dead-centre position, corresponding to partial depression of the treadle, when both circuits are de-energised, and full depression of the treadle serving to energise the circuit of valve 96. Switch 102 is operated by a plunger 145 biased normally to open the switch, and switch 103 is operated by a plunger 146 biased normally to close the switch. A pin 147 carried on arm 64 is so arranged that when the machine is stopped, with lever 56 moved fully counter-clockwise, pin 147 depresses plunger 145, and when the machine is running, with lever 56 moved fully clockwise, pin 147 depresses plunger 146, whereby switches 102, 103, are both closed when the machine is stopped and are both open when the machine is running. Closing switch 100 thereby normally serves to energize valve 95 for opening the work clamp, and partial depression of the treadle serves to close the latter, the work-clamp being reopened when the treadle is released. Full depression of the treadle energises valve 96 for starting the machine, lever 56 being latched in the running position and switches, 102, 103, being open, whereby accidental opening of the work clamp or stopping of the machine is prevented during the stitching cycle. In a modification, the clamp-lifting valve 95 and the stop-motion control valve 96 are controlled by separate treadles each of which incorporates a double-pole two-way switch.