Patent GB-180882-A (GB)
Title: Apparatus for cancelling electrical signals
IPC: B66B19/06
Filed: 1921-05-10
Abstract: 180,882. Railing, M. J., and Connaughton, J. J. V. May 10, 1921. Mine signalling systems.-Relates to apparatus for cancelling visual signals employed in connection with colliery and like winding- engines, and consists in the employment of switches operated by a cam rotating with the engine and sliding axially under the control of a governor. The apparatus operates (1) to cancel signals when the engine starts by the closure of the circuit of a cancelling-magnet, (2) to open the cancelling-circuit as the engine speeds up, thus permitting new signals to be set up, (3) to cancel such new signals as the engine slows down, (4) to re-open the cancelling-circuit as the engine comes to rest. Provision may be made whereby a special cautionary signal is cancelled only when the engine is coming to rest. Fig. 1 shows the mechanism in position when the engine is stationary, and Fig. 4 shows the auxiliary switch being actuated as the engine comes to rest. A cam 9 having two eccentric surfaces 11, 12 and two concentric surfaces 13, 14 is slidably mounted to rotate with a shaft 4 driven from the engine. The shaft 4 carries a centrifugal device comprising a pivoted ring 6 connected by links 8 to the cam, and held in an inclined position by a spring 10. When the speed of the engine rises, the ring 6 moves towards the position in which its plane is perpendicular to the shaft 4, compresses the spring 10, and moves the cam 9 to the right, thus bringing the concentric surfaces 13, 14 under the rollers 19, 20. The rollers operate to close switches 23, 24 when they are raised, and are connected to dash-pots 21, 22 which retard their downward movement. The switches 23, 24 are in series in a circuit including a signal-cancelling magnet 26, and a third switch 27, 28 which is closed when the engine is at rest and opens as the cam 9 moves away at the speeding-up of the engine. In the position shown in Fig. 1, the engine is at rest, and the signalcancelling circuit is open at one or both of the contacts 23, 24. As the engine starts, the rollers 19, 20 are both raised in turn and are both held up by their dash-pots, so that the circuit is completed and the existing signal is cancelled. With an increase in engine speed, the switch 27, 28 is opened, and the contacts 23, 24 held closed independently of the dash-pots by the concentric portions 13, 14 of the cam 9. The opening of the cancelling-circuit permits further signals to be received on the indicator during the running of the engine. As the engine slows down before coming to rest, the cam 9 moves to the left, closing the switch 27, 28 and cancelling any existing signal. When the engine is actually at rest, one or both of the switches 23,24 is open, thus permitting further signals to be set up. If the eccentric portions 11, 12 of the cam 9 are formed as protuberances instead of depressions, the switch 27, 28 may be dispensed with. A separate cautionary signal such as " Men on " may be cancelled only when the engine comes to rest by the switch shown in Fig. 4. A trip member 31 pivoted on a bracket 30, and normally held in alignment by opposed springs 32, 33, is tilted by the passage of a flange 35 on the cam 9. When the speed is rising, the tilting throws outwards the spring 32 but produces no other effect. When the speed is falling, the passage of the flange 35 tilts the trip member 31 into the position shown in Fig. 4, opening the contact 34 and cancelling the cautionary signal.