Patent GB-1244425-A (GB)
Title: Sewing machine
IPC: D05B69/26
Filed: 1969-06-25
Abstract: 1,244,425. Sewing machines. SINGER CO. 25 June, 1969 [1 July, 1968], No. 32021/69. Heading DIG. [Also in Divisions H1 and H2] The electric drive motor of a sewing machine is controlled over a variable speed range by a first circuit including foot pedal operated means 13, Fig. 1, for variably controlling a rectifier 14, release of the foot pedal bringing into operation a second circuit, including the rectifier 14, which causes the motor to operate at a fixed low speed, switch means 41, 42, Fig. 2, in the second circuit being responsive to a predetermined position of the armshaft of the machine to open the second circuit to stop the motor at said predetermined position. Initial depression of pedal 13 closes switch 50, Fig. 2, to close the first circuit, further depression varying the slider 53 of a potentiometer 52 to ' supply a variable reference voltage by way of switch 54 and diode 55 to a potentiometer 56 which varies the reference voltage applied to the gate 57 at cathode 58 of the section controlled rectifier 14. Switch 50, switch 54 and slider 53 are interconnected so that when the foot pedal 13 is released switches 50, 54 are as shown in Fig. 2, whereby the fixed low-speed circuit, in which the reference voltage for the rectifier is set by diode 61, resistor 62 and potentiometer 63 with a shunted zener diode 64. The second circuit is energised through a selector switch 65 which brings in one or other of two red switches 41, 42, corresponding to different stopping positions of the machine. The switches 41, 42 are controlled by stationery permanent magnets 39, 40, Fig. 5, and a magnetic shield ring 36 rotating with the armshaft 11. The selected one of the switches 41, 42 remains closed until a gap 43 in the ring 36 becomes positioned opposite the switch, allowing the associated magnet 39 or 40 to open the switch and break the motor circuit to stop the machine at the selected position. The foot pedal 13 operates a slider to which is attached a pin 78, Fig. 12, sliding in a groove 79. On release of the pedal the pin 78 returns to the position of Fig. 12 which sets switch 65 in the Fig. 2 position for low speed operation and stopping at the selected position. For renewed variable speed operation of the machine pedal 13 is depressed and pin 78 moves past two spring latches 83, 82, and back into groove 79. If before renewing speed operation it is desired to select the second stopping position, pedal 13 is depressed slightly to move pin 78 to a position between latches 83, 87, and then released, whereby pin 78 moves latch 83 anticlockwise to operate bar 84 to change over switch 65 to select the second switch 41 or 42 whereupon the machine moves to the second stopping position. The motor drives a ring gear 17, Fig. 3, rotatably mounted on and driving through a pawl a notched ring 18 rotatably mounted on a stepped hub 19 secured to the armshaft 11, ring 18 being connected by a torsion spring 22 to the hub and the rings 17, 18, forming a oneway clutch. A hand-wheel 28 is connected through lost motion to the shaft 11. Initial movement of the handwheel in the reverse direction to take up the lost motion first disengages the pawl (25) Fig. 6 (not shown) from the wheel 18 to allow manual repositioning of the armshaft 11 without disturbing the position of gear 17.