Patent GB-669398-A (GB)
Title: Improvements in or relating to clockwork time delay mechanisms
IPC: H01H7/12
Filed: 1948-12-18
Abstract: 669,398. Electromagnetic interrupters. LINDARS, H. Dec: 19, 1949. [Dec. 18, 1948] No. 32801/48. Class 38 (v). [Also in Group: XXXV] A clockwork time-delay mechanism comprises a driving spring 1, escapement means 4, means, 8, 9, 10, maintained operable by the unwinding of the spring for winding faster than it unwinds, the difference determining the time-delay period, and delay means 11, 19 operated by the spring to stop the winding thereof during the operating period of the delay means and preferably for effecting a desired operation at the end of the period. In one form the clockwork time-delay mechanism, for delaying e.g., the anode supply to a magnetron, comprises a clockwork motor 2; the driving spring 1 of which is wound by an electromagnet 10 at a greater rate than it unwinds, the difference in the rates being utilised to effect a delayed switching-on of the anode-supply by a solenoid 29 when the mains switch 33 is closed. The magnet 10 actuates a pawl 9 and a ratchet wheel 8 which is keyed to the winding arbor 5 of the motor 2. The arbor also has keyed thereto an arm 12 and cam discs 11, 19. When the spring is unwound the arm closes contacts 14 to put the magnet 10 in circuit with the mains 15 and the disc 19 closes normally-open contacts 21 to place solenoid 25 in circuit. On closing the mains switch 33 the magnet 10 winds up the spring, the arm 12 moving away from the contacts 14, and the solenoid 25 closing its contacts 24, 26. The motor 2 rotates a star-cam 22 to close intermittently its contacts 23 in series with the magnet 10. The spring is gradually wound up until the disc 11 opens normally-closed contacts 27, in series with the solenoid 25. which is thereby de-energized to open contacts 24, 26, thus open-circuiting magnet 10, having previously closed normallyopen contacts 28 thereby energizing the solenoid 29 which closes its hold-in contacts 30 and the anode-supply contacts 31. The spring continues to unwind until the cam discs 11, 19 open contacts 28 and close contacts 27, 21 whereupon solenoid 25 is energized and the magnet 10 winds up the spring until the current to the solenoid is interrupted again. This process is cyclically operated until the switch 33 is opened. The relative positions of the discs 11, 19 are variable by means of a slot 18 on the disc 19, so that the point at which the contacts 21 open as the spring approaches the fully-wound condition may be varied. If a short interruption of the mains supply should occur, the magnet 10 and the solenoids are de-energized, the motor 2 driving the arbor 5 and the discs 11, 19 to the unwound position and if before this is reached, the supply is restored, since the contacts 21, 27 are closed, the solenoid 25 and the magnet 10 are energized and the spring is then wound up until the disc 11 energizes the solenoid 29. If the interruption is long enough to allow the spring to be completely unwound, the arm 12 closes the contacts 14 and the delay mechanism operates through the whole cycle when the supply is restored. In a modification, Fig. 2 (not.shown), the spring is anchored at one end to a drum on a loose sleeve rotatable on the arbor 5 and carrying a disc on which are mounted the contacts 14, 21, 27, 28.