GB1361687A - Speed reducing apparatus for a fabric laying machine - Google Patents

Abstract

1361687 Laying fabric CUTTERS MACHINE CO INC 1 Feb 1972 [18 March 1971] 4587/72 Heading D1S A speed reducing apparatus for a fabric laying machine 10 having a frame 11 supported for reciprocation over a laying table 14 between reversing stations, a fabric laying unit 21 and means for supplying fabric 17 to the unit 21, comprises (a) electrically energized motor drive means 28 for moving the frame 11 over the table 14; (b) speed control means for selectively energizing the motor 28 to move the frame 11 at a low speed or to move the frame 11 at a high speed substantially faster than the low speed; (c) a dynamic braking circuit 46 connected to the motor 28; (d) low speed switch means communicating with the dynamic braking circuit 46 and with the speed control means, the low-speed switch means being adapted, when actuated, to energize the dynamic braking circuit while the back EMF of the motor 28 is above a pre-set value corresponding to the low speed, to condition the speed control means to de-energize the motor 28 while the dynamic braking circuit 46 is energized, and to condition the speed control means upon de-energization of the dynamic braking circuit to energize the motor 28 in the low speed; and trip means 55, e.g. a ramp, for actuating the low speed switch means while the frame 11 is moving toward a reversing station. Automatic energisation of the dynamic braking circuit 45, upon signal, causes the motor 28 to be decelerated down to, but not below, the pre-set low speed, at which time the circuit 46 is de-energized and the speed control drive mechanisms are re-energized to drive the motor 28 at a constant low speed. The low speed switch means comprises a trigger circuit 47 including a pair of low speed switches 49, 50, a speed selector switch 62 having a high position and a low position and a dynamic brake switch 70. The switch 62 communicates with the speed control means to selectively energize the motor 28 in high speed in high position and low speed in low position and the switch 70 is adapted to energize the circuit 46 when closed. The switch 62 is in low position and the switch 70 is closed when the switch 49 or 50 is actuated. The dynamic braking circuit 46 comprises an SCR 72 in series with a braking resistor 73 and a transistor 74 to apply a constant voltage upon the circuit 46 corresponding to the low speed and opposite in direction to the back EMF so that the SCR 72 turns off when the back EMF is equal to or less than the constant voltage, the switch 70, when closed, being adapted to turn on the SCR 72. A Zener diode 75 is connected in the base-collector circuit of the transistor 74 and a resistor 76 is connected in the base-emitter circuit of the transistor 74. While the circuit 46 is energized, a signal is transmitted to a stop-start control circuit 38 to close a switch in a clamping circuit 80 so that a motor speed control circuit 37 is de-energized so that an SCR bridge circuit 45 is not fired, regardless of the setting of the switch 62, so that the motor 28 is not driven.